Milk Thistle (Silybum marianum)

Indications and Efficacy

Milk thistle, or silybum marianum, has been described in the literature for hundreds of years as an herbal remedy for a number of physical and mental ailments. Research indicates that it may have anti-cancer, anti-inflammatory, anti-diabetic, and anti-oxidant qualities and is used in many countries for liver disorders, including cirrhosis and hepatitis.

Milk thistle is generally available in nutritional stores as a capsule (in a variety of doses). The exact mechanism of milk thistle in psychiatric illnesses is not clearly understood, although the theory is that the flavanoid complex silymarin may increase serotonin levels in the cortex.

Obsessive Compulsive Disorder. Milk thistle demonstrated efficacy in one double-blind trial of 35 patients with moderate to severe OCD randomized to receive either milk thistle extract (in the form of a pill; 200mg by mouth three times per day) or fluoxetine (10mg by mouth three times per day. At the end of the trial, both treatment groups demonstrated significant symptom severity improvement.

Initiation and Ongoing Treatment

The target dose of milk thistle is 600mg per day.

Dose changes should follow a systematic approach whereby dose titration should start at 200mg a day (after a meal) and be increased over a period of a couple weeks to 600mg a day (200mg three times a day after each meal) based on clinical assessment of improvement and adverse events.

An example of a possible dose titration schedule is:

Day 1: 200mg by mouth after breakfast each day

Day 7: 200mg by mouth twice per day (after breakfast and


Day 14: 200mg by mouth three times per day (after each meal)

Dosages should only be increased based on clinical severity and improvement as determined by the treating physician.

Any benefit for OCD may require at least 5-6 weeks of treatment.

Risks and Side Effects Risks

Milk thistle may cause an allergic reaction in people who are sensitive to the Asteraceae/Compositae plant family or to daisies, artichokes, common thistle, kiwi, or to any of milk thistle’s constituents

(silibinin, silychistin, silydianin, silymonin, siliandrin). Anaphylactic shock (a severe allergic reaction) from milk thistle tea or tablets has been reported in several patients. It should not be prescribed for individuals with an allergy to this family of plant.

Milk thistle may interact with different medications by reducing their breakdown in the liver and thereby increasing their serum levels. Medications metabolized by cytochrome P450 2C9 (e.g., phenytoin, tamoxifen, glipizide, warfarin, diazepam), cytochrome P450 3A4 (e.g., ketoconazole) or by glucuronidation (e.g., digoxin, estrogen, lamotrigine, morphine) may be affected by milk thistle. Before starting milk thistle, patients should talk with their physicians.

Side Effects

The most common side effects reported with milk thistle treatment include diarrhea, bloated feeling, nausea, and loss of appetite.

Contraindications/Special Considerations

Pregnancy/breast-feeding. A limited amount of information is available regarding the use of milk thistle in pregnancy or breast-feeding women. As such, treatment with milk thistle is not recommended in this population.

Breast cancer, ovarian cancer, or uterine cancer. In hormone-sensitive conditions such as these, milk thistle extract might act like estrogen. As such, for female patients in treatment or remission from cancer, milk thistle is contraindicated.

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