Milk Thistle Supplements Review

Find the Best Milk Thistle Supplement. Tests and Reviews of Popular Milk Thistle Supplements & CL's Top Picks.

Medically reviewed and edited by Tod Cooperman, M.D.

Last Updated : 07/30/2021 | Initially Posted: 08/01/2020

Milk Thistle and Liver Formula Supplements Reviewed by ConsumerLab.com

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Table of Contents

Summary

· What does milk thistle do? For people with type 2 diabetes, milk thistle may decrease blood sugar, hemoglobin A1c, and LDL cholesterol levels when used with conventional therapy. The evidence is mixed as to whether it improves liver function in people with chronic active hepatitis (see What It Does).

· What is silymarin? Silymarin is the term for a specific group of chemically-related compounds found in milk thistle. Silymarin is thought to be responsible for some of the herb's effects and is used as a marker of milk thistle strength (see What It Is).

· What to look for with milk thistle? Milk thistle comes in various forms and concentrations, but most clinical studies of milk thistle's effectiveness have used extracts at a dose of about 200 mg of extract taken 2 to 3 times per day. The amount of silymarin in these extracts is about 58% of its weight (although this has been reported as 80% when using a non-specific, older method of testing known as UV-VIS) (see ConsumerTips™ for dosage and other details).

· What did CL find in its tests of milk thistle supplements? The amount of silymarin per serving ranged from 61.2 mg to 202 mg. For most products, these amounts were far less than a consumer might expect from labels, leading CL to rate several products as having poor labeling (see What CL Found).

· Which is the best milk thistle supplement? Among products Approved for Quality by ConsumerLab.com one was chosen as CL's Top Pick for providing a substantial amount of silymarin, appropriate usage instructions, and superior value.

· What are the side effects of milk thistle? Milk thistle is generally well tolerated but, infrequently, can have a laxative or other gastrointestinal side-effect. Allergic reactions can occur, especially in people who are sensitive to related plants and it may interact with certain medications (see Concerns and Cautions for details).

What It Is:

The ripe seeds of the milk thistle plant (Silybum marianum) are used medicinally. One of the most important constituents of milk thistle is silymarin, which itself has several chemical constituents of which most prominent is silybinin (also referred to as silibinin or silybin).

What It Does:

Diabetes
The silymarin component of milk thistle may decrease blood sugar, hemoglobin A1c, and LDL cholesterol levels when used with conventional therapy in people with type 2 diabetes, as shown in a 4-month, placebo-controlled study in Iran which 200 mg of a milk thistle extract was given 3 times daily (Huseini, Phytother Res 2006). A milk thistle extract also appeared to reduce insulin resistance in people with coexisting diabetes and alcoholic cirrhosis in a 12-month study in Italy in which an extract providing 200 mg of silymarin was taken 3 times daily given; however, the study was not placebo-controlled (Velussi, J Hepatol 1997).

Hepatitis and Diseases of the Liver
Silymarin is thought to act as a liver-protectant, although evidence of benefit in liver disease has been mixed. One preliminary study of a specific silybinin preparation improved liver function in people with chronic active hepatitis. However, most studies in patients with hepatitis B or C have not shown an improvement in mortality or liver function using milk thistle or preparations of milk thistle. Similarly, in alcoholic liver disease, some preliminary clinical studies suggested that milk thistle might improve liver function and mortality, but later studies did not show a significant effect.

Some research has shown benefit of milk thistle in people with nonalcoholic steatohepatitis (NASH), a condition marked by excessive storage of fat in the liver and ballooning of liver cells. However, the studies have been small and short-term, so larger studies conducted over longer periods of time are needed to confirm the effectiveness. A study in Iran among 64 people with NASH showed that the silymarin component of milk thistle, taken in doses of 70 mg three times daily for 8 weeks (Livergol, Goldaru Pharmaceutical Company), reduced markers of liver injury compared to placebo, although these markers of liver injury improved in the placebo group as well (Solhi, Caspian J Intern Med 2014). Another small study in Malasia among 89 people with confirmed NASH also showed that taking silymarin in much higher doses, longer-term (700 mg three times daily for 48 weeks) reduced markers of liver injury and reduced fibrosis compared to placebo. However, taking silymarin did not increase the percentage of patients who showed at least 30% improvement in liver injury based on NAFLD Activity Score, which was the primary outcome of the study, nor did it improve steatosis or liver cell ballooning or prevent the development of fibrosis (Kheong, Clin Gastroenterol Hepatol 2017).

Liver Protection from Chemotherapy and Other Drugs
Preliminary evidence suggests that milk thistle extract standardized to 70% - 80% silymarin may protect the liver against damage from certain toxins, including drugs such as acetaminophen and phenytoin (Dilantin). Milk thistle extract may also reduce liver toxicity associated with chemotherapy -- a complication which can limit therapy. In a study of children with acute lymphoblastic leukemia (ALL) receiving maintenance chemotherapy, milk thistle extract standardized to 33% silybinin was given at a daily dose of 80 mg to 320 mg of silybinin (Ladas, Cancer 2010). Although no benefit was seen during the short course of therapy (28 days), one month later the milk thistle-treated children had reductions in levels of liver enzymes that indicate toxicity compared to those who did not receive milk thistle.

Administered intravenously (IV), silybinin may lessen liver damage due to poisoning by Amanita phalloides mushroom (death cap) -- although this IV preparation is not readily available in the U.S.

Menopause
Milk thistle may help reduce the severity and frequency of hot flashes in postmenopausal women, as shown in a placebo-controlled study in Iran, in which 200 mg of a milk thistle extract or placebo was given twice daily for 8 weeks to 73 postmenopausal women (average age 52). After 8 weeks, women given milk thistle extract reported about 3 fewer hot flashes per day compared to baseline. This improvement persisted for 4 weeks after they stopped taking the supplement. Women given milk thistle extract also reported less severe hot flashes when they did occur. Women given milk thistle reported a 68% reduction in hot flash severity after 8 weeks (from 5.25 points to 1.70 points based on a 10 point-scale). The frequency and severity of hot flashes remained unchanged for women in the placebo group. The milk thistle extract was standardized to 80% total silymarin (47.7% silibinin) (Saberi, Phytother Res 2020). Note that women with very severe symptoms were excluded from the study, so it is uncertain if milk thistle would be beneficial in such cases. See CL's Menopause Supplements Review, covering soy and red clover isoflavones, black cohosh, and progesterone cream, for information about other ingredients commonly used for menopause.

Other:
Silybinin is under investigation for use in preventing or treating various forms of cancer, especially prostate cancer.

For information about dosage, see What to Consider When Using section below.

Quality Concerns and Tests Performed:

Most clinical studies of milk thistle's effectiveness have used specific dry extracts standardized to approximately 70% to 80% silymarin on a weight basis based on non-specific testing methods or about 58% using a High Performance Liquid Chromatography (HPLC) specific for silymarin. Milk thistle is also available in non-concentrated, seed powder form, which should contain at least 2% silymarin. ConsumerLab.com purchased and tested milk thistle products by HPLC to determine which products contained this level of silymarin -- and/or other levels if claimed on labels.

Past testing by ConsumerLab.com has revealed many milk thistle products that do not contain these expected amounts. Any product containing whole herbs (including milled, milk thistle seed powder) was also tested for contamination with the heavy metals lead, cadmium and arsenic, as this can occur in herbal supplements — although is less likely with extracts, and for yeast and mold contamination.

Testing of 19 milk thistle extract supplements purchased from the U.S. and seven more from the Czech Republic found that seven from the U.S., and three from the Czech Republic, contained detectable levels of one or more of five synthetic pesticide-related ingredients (i.e., pirimiphos-methyl, malathion, and chlorpyrifos, which are insecticides; carbendazim, a fungicide; and piperonyl butoxide, a component added to enhance the potency of certain pesticides) in amounts that would be considered unsafe for infants and babies, as they exceeded the European Union (EU) maximum residue levels of 10 mcg/kg. One of the products from the U.S. and one from the Czech Republic contained levels that exceeded EU maximum residue levels for adults. At least one of the pesticides (chlorpyrifos) detected in some of the milk thistle products has been reported to cause liver and kidney toxicity when given orally to mice. All of the evaluated milk thistle products (specific brand names were not provided), which were purchased between 2016 and 2017, contained milk thistle extract or seed extract. Some, although not all, of the products also contained other herbal ingredients (Fenclova, Sci Rep 2019). These results were not published until 2019, around the time of ConsumerLab's current review. In light of the findings, ConsumerLab.com may evaluate pesticides in milk thistle products in its next review.

What CL Found:

When choosing a milk thistle supplement made from an extract (as most are), you want one that provides a significant amount of silymarin -- about 58% (or at least 52.2% allowing for acceptable variance) of the extract's weight when measured with a highly specific test method known as HPLC. This is the test method used by ConsumerLab and is the official USP method (see How Products Were Evaluated). What causes great confusion in the market is that many extracts are labeled as providing 80% silymarin, likely based on an older, non-specific method of testing known as UV-VIS. Finding 58% silymarin by HPLC is equivalent to finding 80% silymarin by UV-VIS because the UV-VIS method incorrectly counts some non-silymarin compounds as being silymarin. The FDA allows manufacturers to use any testing method they want.

Some manufacturers are clear about this and tell you, right on the label, the percent silymarin and the method used. Others only tell you the percent silymarin without the method. Since the only official compendial method is HPLC, if a product claims 80% silymarin without disclosing that this is based on the older method, we consider that to be poor labeling, although the product itself may be fine to use and has not violated FDA labeling requirements.

Based on the amounts of silymarin that we found in testing among the nine milk thistle supplements that we selected for review, here is what we found:

· Approved: California Gold (claims 80% silymarin flavonoids by UV-VIS and 58% by HPLC) and Jarrow Formulas (claims 80% total flavonoids, which implies silymarin and other flavonoids as included in UV-VIS).

· Approved but with "Poor Labeling": (CVS Health, Nature's Sunshine, Pure Encapsulations, and Swanson). These products contain significant concentrations of silymarin — meeting our minimum requirements, but did not state that their claimed "80% silymarin" (or claims to that effect) were apparently based on a non-specific test method, as we found the extracts in these products to provide 57.2%, 57.7%. 54.9%, and 53% silymarin, respectively.

· Approved but with "Low Strength": TruNature Premium Milk Thistle contains a much smaller amount than other products of silymarin as confirmed by CL (and which is listed as silybin, the basic chemical name for silymarin compounds), although it does include phospholipids that may increase absorption.

· NOT Approved: NOW Silymarin and Vitamin Shoppe Milk Thistle Extract. NOW claims 280 mg of silymarin but we found only 174.7 mg by HPLC, and Vitamin Shoppe claims 240 mg of silymarin but we found only 154 mg. This also means that these extracts are less concentrated than the others, at 49.9% and 51.3% silymarin, respectively — too far below our minimum of 58%. The amounts of silymarin they provide, however, remain significant.

Amounts of silymarin found in products
Although we didn't like the way that many milk thistle extracts were labeled (as explained above), the graph below shows that most provided substantial amounts of silymarin, although not as much as one might think from the claims on the labels.

Unfortunately, the only two products that CL Approved without qualification, California Gold and Jarrow, provided among the smallest amounts of silymarin per serving.

Silymarin Found Per Serving

Cost to get silymarin
The cost to get 160 mg of silymarin (a substantial dose, in-line with what has been used clinically per serving), ranged from just 5 cents to 44 cents among the products, as shown in the graph below. The least expensive, Approved product was Swanson Milk Thistle.

Cost per 160mg Silymarin Found

Top Pick:

California Gold could have been our Top Pick for milk thistle if it were designed to provide somewhat more than its 175 mg of extract per capsule, as, otherwise, it was the only product reviewed that clearly stated its silymarin content — both in terms of HPLC (58%) and UV-VIS (80%), and we found it to meet its claim based on our HPLC analysis. It also had the second highest concentration of silymarin, at 62.9% based on the amount we found (only Jarrow was higher at 67.6%). It is also reasonably priced at 11 cents per large capsule.

Our Top Pick, however, is Swanson Milk Thistle, despite the fact that its claimed 80% silymarin (i.e., 200 mg) from its extract was likely based on UV-VIS, as we found 137.5 mg based on HPLC analysis, which included about 5 mg expected from its other ingredient, milk thistle seed powder. This is still a substantial amount of silymarin per capsule and 27.5 mg more per capsule than in California Gold, while costing about half the price -- only 6 cents per large capsule. Swanson's suggestion of taking two to three capsules per day with water is also consistent with how milk thistle is best taken, while California Gold suggests only one capsule daily with food, which is unusual.

Going forward, it would be great for consumers if Swanson and other brands would list their silymarin content based on the official USP method, HPLC, while optionally indicating the amount of silymarin by UV-VIS.

Test Results by Product:

Listed alphabetically below are test results for nine milk thistle products selected for testing by ConsumerLab.com. Products listed as "Approved" met their label claim or minimum expected amount of silymarin and ConsumerLab.com's additional standards for milk thistle supplements (see Passing Score). Silymarin claims and amounts are shown in the 2^nd column. Labeled serving suggestions and a description of pill sizes are in the 3^rd column. Cost and price comparisons are shown in the 4^th column; notable features and precautions are in the 5^th column; and full list of ingredients for each product is found in the final column.

Results of ConsumerLab.com Testing of MILK THISTLE SUPPLEMENTS

(Click arrows or swipe left or right to see all columns)

Approval Status

Product Name
(Suggested Serving on Label)

Claimed Amount of Milk Thistle

Claimed or Expectedⓘ Amount of Silymarinⓘ

Pill Sizeⓘ

Suggested Serving on Label

Cost for Suggested Serving

[Cost Per 160 mg of Silymarin]

Priced

Notable Features

Full List of Ingredients Per Serving

Milk Thistle Extracts:

APPROVED

California Gold Nutrition® EuroHerbs™ Milk Thistle

Dist. by California Gold Nutrition®

$ Price Check

1 veggie capsule

175 mg extract

101.5 mg silymarinⓘ (C)
✔
Met claim of 58% silymarin by HPLC (found 110 mg or 62.9% of extract).

Large veggie capsule

Take 1 veggie capsule daily with food.

$0.11/veggie capsule

[$0.18 based on amount listed]
[$0.16 based on amount found]

$20.00/180 veggie capsules

This product is not manufactured with milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soy or gluten.

Precaution: Produced in a third-party, audited and registered cGMP compliant facility that may process other products that contain these allergens or ingredients.

1 veggie capsule
Milk Thistle Extract (Silybum marianum, seed/fruit) [Standardized to 80% total silymarin flavonoids/ flavonoligans via UV-VIS; 58% via HPLC] 175 mg.

Other Ingredients: Veggie Capsule (Modified Cellulose, Chlorophyll [as Sodium Copper Chlorophyllin]), Organic Rice Concentrate.

APPROVED

But Poor Labeling

CVS Health™ Milk Thistle 250

Dist. by CVS Pharmacy, Inc.

1 capsule

250 mg extract

200 mg silymarin (C)
Found only 143 mg by HPLC (71.5% of listed amount)
[57.2% of extract]

Large capsule

For adults, take one (1) capsule three times daily, preferably with meals.

$0.13/capsule

[$0.11 based on amount listed]
[$0.15 based on amount found]

$26.99/200 capsules

No yeast, wheat, gluten, milk or milk derivatives, lactose, sugar, preservatives, soy, artificial color, artificial flavor, salt.

1 capsule
Milk Thistle Extract (Silybum marianum) (seed) (standardized to contain 80% Silymarin, 200 mg) 250 mg.

Other Ingredients: Gelatin (Porcine and Bovine), Dicalcium Phosphate, Maltodextrin, Stearic Acid, Microcrystalline Cellulose, Magnesium Stearate, Croscarmellose Sodium and Silica.

APPROVED

Jarrow Formulas® Milk Thistle

Dist. by Jarrow Formulas®

$ Price Check

1 veggie cap

150 mg extract

120 total flavonoids (C)

Found 101.4 mg silymarin by HPLC
[67.6% of extract]

Medium/large veggie cap

Take 1 to 3 capsules per day or as directed by your qualified healthcare professional.

$0.08/veggie cap

[$0.13 based on amount found]
Lowest cost for silymarin among Approved products

$8.18/100 veggie caps

Suitable for vegetarians/ vegans. Gluten Free. Non GMO Certified by NSF® seal. No wheat, gluten, soybeans, dairy, egg, fish/ shellfish, or peanuts/ tree nuts.

1 veggie cap
Milk Thistle Seed 30:1 Extract (Silybum marianum) (80% [120 mg] Total Flavonoids) 150 mg.

Other Ingredients: Cellulose, magnesium stearate (vegetable source) and silicon dioxide. Capsule consists of hydroxypropyl-methylcellulose.

APPROVED

But Poor Labeling

Nature's Sunshine® Milk Thistle

Dist. by Nature's Sunshine Products, Inc.

1 tablet

350 mg extract

280 mg silymarin (C)
Found only 202 mg by HPLC (72.1% of listed amount)
[57.7% of extract]

Medium/large tablet

Take 1 tablet with a meal twice daily.

$0.51/tablet

[$0.29 based on amount listed]
[$0.40 based on amount found]

$30.50/60 tablets

Time Release.

1 tablet
Milk Thistle Seed Extract (Silybum marianum) [Silymarin 280 mg] 350 mg.

Other Ingredients: Dicalcium phosphate, cellulose, stearic acid (vegetable).

NOT APPROVED

NOW® Silymarin

Dist. by Now Foods

1/8 level tsp of powder [0.35 g]

350 mg extract

280 mg silymarin (C)
Found only 174.7 mg by HPLC (62.4% of listed amount)
[only 49.9% of extract]

Powder in container

Take 1/8 level teaspoon daily in juice or water, with food.

$0.05/0.125 level tsp

[$0.03 based on amount listed]
[$0.05 based on amount found]

$16.19/4 oz [113 g] bottle (approx. 323 servings)

Kosher. Non-GMO. Not manufactured with yeast, wheat, gluten, soy, corn, milk, egg, fish, shellfish or tree nut ingredients.

1/8 level tsp
Milk Thistle Extract (Silybum marianum) (Fruit/Seeds) (Standardized to 280 mg Silymarin Flavonoids - equivalent 80%) 350 mg.

Other Ingredients: None.

APPROVED

But Poor Labeling

Pure Encapsulations® Silymarin

Mfd. by Pure Encapsulations

1 capsule

250 mg extract

200 mg silymarin (C)
Found only 137.2 mg by HPLC (68.6% of listed amount)
[54.9% of extract]

Medium/large capsule

Take 1 capsule, 1-4 times daily, between meals.

$0.29/capsule

[$0.23 based on amount listed]
[$0.33 based on amount found]

$34.30/120 capsules

Gluten-Free.

1 capsule
Milk thistle (Silybum marianum) extract (seed) (standardized to contain 80% silymarin) 250 mg.

Other Ingredients: Vegetarian capsule (cellulose, water).

APPROVED

But Low Strength

Trunature® [Costco] Premium Milk Thistle

Dist. by Costco Wholesale Corporation

1 vegetarian capsule

160 mg phytosome

52 mg silybin (C)
✔
Met claim of 52 mg silybin but provides relatively small amount of silymarin (61.2 mg by HPLC).

Medium/large vegetarian capsule

1 capsule per day. For additional liver support: 1 capsule 2-3 times per day.

$0.17/vegetarian capsule

[$0.44 based on amount found]

$19.99/120 vegetarian capsules

1 vegetarian capsule

Calcium 42 mg

No Soy. No Sugar. No Artificial Colors or Flavors. No Gluten. No Salt. No Lactose.

1 vegetarian capsule
Calcium (dicalcium phosphate) 42 mg, Siliphos® Milk Thistle Phytosome (Silybum marianum) extract (seed); phospholipids (sunflower lecithin) [Silybin 52 mg] 160 mg.

Other Ingredients: Vegetarian capsule (hypromellose, purified water), silica, croscarmellose sodium, magnesium stearate (vegetable grade).

NOT APPROVED

Vitamin Shoppe® Milk Thistle Extract

Dist. by Vitamin Shoppe, Inc.

1 capsule

300 mg extract

240 mg silymarin (C)
Found only 154 mg by HPLC (64.2% of listed amount)
[only 51.3% of extract]

Large capsule

Take one (1) capsule daily, preferably with a meal.

$0.11/capsule

[$0.08 based on amount listed]
[$0.12 based on amount found]
$22.90/200 capsules

Does not contain: Gluten, Sugar, Salt, Artificial Colors or Flavors. Gluten free. Dairy free. Soy free. Nut free.

1 capsule
Milk Thistle Extract (Silybum marianum) (seed) (std. to contain 80% Silymarin (240 mg)) 300 mg.

Other Ingredients: Microcrystalline cellulose, gelatin, magnesium stearate, silicon dioxide.

Milk Thistle Extract and Powder Combination:

APPROVED

But Poor Labeling

Top Pick

Swanson® Milk Thistle

Dist. by Swanson Health Products

1 capsule

250 mg extract

250 mg powder

205 mg silymarin (C + M)ⓘ
Found only 137.5 mg by HPLC (67% of expected amount)
[53% of extract, assuming 5 mg from powder]

Also, tested for heavy metalsⓘ, mold & yeastⓘ
✔

Large capsule

Take one capsule two to three times per day with water.

$0.06/capsule

[$0.05 based on amount expected]
[$0.07 based on amount found]

$7.59/120 capsules

None.

1 capsule
Milk Thistle Seed Extract (Silybum marianum) (standardized to 80% silymarin) 250 mg, Milk Thistle Seed (Silybum marianum) 250 mg.

Other Ingredients: Gelatin.

Unless otherwise noted, information about the products listed above is based on the samples purchased by ConsumerLab.com (CL) for this Product Review. Manufacturers may change ingredients and label information at any time, so be sure to check labels carefully when evaluating the products you use or buy. If a product's ingredients differ from what is listed above, it may not necessarily be of the same quality as what was tested.

The information contained in this report is based on the compilation and review of information from product labeling and analytic testing. CL applies what it believes to be the most appropriate testing methods and standards. The information in this report does not reflect the opinion or recommendation of CL, its officers or employees. CL cannot assure the accuracy of information.

ConsumerTips™:

What to Consider When Buying:
Extracts vs. Seed Powder:
Dry milk thistle seed powder contains only 1.5% to about 3.0% silymarin (or 2% when tested by HPLC according to the United States Pharmacopoeia (USP)), while dry "extracts" are much more concentrated -- with silymarin accounting for approximately 80% of their weight by UV-VIS but only about 58% by HPLC. Consequently, pills made from seed powder contain relatively little silymarin (about 10 mg per 200 mg of powder) while pills made from dry extracts generally provide more than 100 mg of silymarin. People who prefer to use whole herb products as opposed to concentrated extracts should be aware that much larger doses of milk thistle will be necessary to get the same amount of silymarin and, as found in a previous Review, may be more likely to be exposed to contaminants, such as lead.

Be aware that "liquid extracts" are not necessarily concentrated extracts. One liquid extract product tested by ConsumerLab in a previous Review indicated that it was made from milk thistle "seed" as opposed to a "seed extract." Products like this are not concentrated -- this particular product was expected to contain only 7.5 mg of silymarin per mL (although testing showed it to actually provide less than 2 mg).

Serving recommendations also range widely from 1 to 4 servings per day.

Other Ingredients in "Liver" Formulas:
Milk thistle is often used in "liver" formulations which include additional ingredients. Be aware that, in most cases, these formulations (which are typically more expensive that a straight milk thistle product) have not been clinically tested. A common ingredient in such formulas is artichoke extract, which may help relieve digestive pain by stimulating the gall bladder and liver (Salem, Plant Foods Hum Nutr 2015; Holtmann, Aliment Pharmacol Ther 2003). Another is schizandra fruit extract (also spelled schisandra), for which preliminary evidence suggests a liver benefit. Other common ingredients in liver formulas include dandelion root extract -- a "liver tonic" in traditional folk medicine with little supporting scientific evidence, and phyllanthus, which has been used in treating hepatitis B but with questionable benefit.

What to Consider When Using:
The common dosage of milk thistle is 200 mg 2 to 3 times a day of an extract standardized to 70% to 80% silymarin by UV-VIS, which is approximately 58% by HPLC. The reason why it is taken more than once a day is the relatively short half-life of silymarin of just 1-2 hours (Hawke, J Clin Pharmacol 2010). Taking milk thistle extract without food may allow silymarin to be more quickly absorbed, according to information from Floridis which sells a form of milk thistle extract, Legalon, used in clinical studies. Legalon is produced by the German company, Madaus, and product information indicates that the extract is at least 58% silymarin tested by HPLC.

For diabetes, the 200 mg is taken 3 times a day along with conventional treatment. For cirrhosis of the liver, a daily dose of 420 mg has been used (expected to contain about 300 to 330 mg of silymarin). For chronic active hepatitis, 240 mg of silybinin (the major constituent of silymarin) taken twice daily has been used. (Among the products tested in this review, silybinin was generally found to account for 30% to 65% of the total silymarin.) There is some evidence that preparations containing phosphatidylcholine may increase absorption of active ingredients of milk thistle. Phosphatidylcholine would be expected in the Trunature Premium Milk Thistle product tested in this Review, as it contains lecithin, as source of phosphatidylcholine.

As a liver-protectant during chemotherapy, milk thistle extract providing 80 mg to 320 mg of silybinin per day has been used in children, with the dosage based on weight (approximately 5.1 mg of silybinin daily per kilogram of body weight) (Ladas, Cancer 2010).

For treatment of mushroom poisoning with Amanita phalloides, 20 mg to 50 mg of silybinin per kg of body weight has been administered intravenously over 24 hours, divided into four infusions, each administered over a two hour period. Intravenous silybinin, however, is not available in the U.S.

Silymarin has a relatively short (1 to 2 hour) half-life and low bioavailability. A short-term (7 day) study in non-cirrhotic patients with hepatitis C showed that much higher doses of silymarin (as much at 700 mg three times per day) could be given without causing adverse events. Plasma levels of silymarin were dramatically increased. However, even these high doses did not cause meaningful reductions in markers of hepatitis viral activity (Hawke, J Clin Pharmacol 2010).

Concerns and Cautions:

Milk thistle and its extracts are generally well-tolerated but, infrequently, can have a laxative effect and cause other gastrointestinal side-effects. Some patients may have allergic reactions to milk thistle including itching, rash, hives, eczema, and anaphylaxis. Allergic reactions may be more likely to occur in patients sensitive to plants such as ragweed, chrysanthemums, marigolds, and daisies. Milk thistle might reduce the effectiveness of oral contraceptives. Milk thistle may inhibit the enzyme CYP2C9, that is involved in metabolizing (breaking down) certain drugs, thereby increasing the levels of such drugs, including amitriptyline, diazepam, verapamil, and warfarin. For example, approximately four weeks after taking a "liver cleanse" supplement containing 200 mg of milk thistle, a man in his 30s taking warfarin (36.5 mg per week) as a blood thinner experienced an increase in his INR (a measure of blood clotting time) from 2.64 to 4.12 despite it having been previously stable. His INR returned to its normal level one week after stopping the supplement. The supplement contained other ingredients, none of which are known to interact with warfarin (Lash, J Clin Pharm Ther 2019).

Milk thistle can be contaminated with yeast and mold (fungi) which create potentially harmful toxins. These organisms are known to grow on milk thistle if not properly dried and stored after harvest. An analysis of milk thistle products in the U.S. (Tournas, Int J Food Microbio 2013) found that 100% of seed powders (14 of 14 samples) and herb powders (7 of 7) were contaminated with yeast or mold, as were 88% of whole seed products (30 of 34 samples), and 71% of cut herb products (10 of 14). However, none of the milk thistle supplements sold as tea bags, alcohol-based seed extracts, oil-based seed extracts, capsules, or soft gels contained yeast or mold. A study which looked for fungal toxins (mycotoxins) in supplements found that 28% (9 of 32) contained about 30% to 75% of the daily tolerable intake amount. Four of these were capsules (out of a total of 23 capsules/tablets), although all were from the Czech Republic or Slovakia while products from other countries (the U.S. was not included) had little or none (Veprikova, J Ag Food Chem 2015). (In this Review, ConsumerLab.com tested any products containing seed ingredients (such as seed powder) for yeast and mold.) Since mycotoxins can affect the liver, it seems prudent for people with liver disease to avoid milk thistle sold as whole seed, cut herb, or powders and to use milk thistle supplements with caution, not taking more than the suggested amount.

Information on this site is provided for informational purposes only. It is not an endorsement of any product nor is it meant to substitute for the advice provided by physicians or other healthcare professionals. The information contained herein should not be used for diagnosing or treating a health problem or disease. Consumers should inform their healthcare providers of the dietary supplements they take.

Latest Clinical Research Updates for Milk Thistle Supplements

Pesticides in Milk Thistle?

7/31/2021

Some milk thistle products may be contaminated with pesticides, according to a study of more than 25 commercially available supplements. Learn more in the Quality Concerns section of our Milk Thistle Supplements Review.

Milk Thistle for Menopause?

8/14/2020

Can taking milk thistle relieve hot flashes during menopause? Learn what a new study showed in the What It Does section of the Milk Thistle Supplements Review. Also see our Top Pick among milk thistle supplements. (Also see our Menopause Supplements Review for information and reviews of products containing soy and red clover isoflavones, black cohosh, or progesterone cream.)

Milk Thistle Interaction

10/22/2019

Milk thistle may interact with certain drugs, as noted in a recent case report. For details see the Concerns and Cautions section of the Milk Thistle Supplements Review. Also see our Top Picks for milk thistle.