Milk thistle (Silybum marianum) has been used for centuries, primarily for liver and gallbladder ailments [1.7.3]. Its active compound, silymarin, is believed to possess antioxidant and anti-inflammatory properties that protect liver cells from toxins [1.7.1, 1.7.5]. Despite its widespread use, understanding its interactions with other substances is critical for safety.
The Question of Vitamin Interactions
Currently, there are no definitive studies or warnings that specify vitamins that absolutely cannot be taken with milk thistle [1.2.2]. However, some sources note theoretical concerns or minor interactions. For instance, milk thistle could potentially interact with supplements like vitamin E, though this is not strongly evidenced [1.2.1]. The more significant issue is that some multivitamin products containing high doses of vitamins A and E may carry their own health risks, independent of milk thistle [1.5.2].
The main focus of contraindication shifts from vitamins to a much broader and more critical category: prescription and over-the-counter medications.
How Milk Thistle Interacts with Medications
The liver is the body's primary metabolic powerhouse, using a family of enzymes known as cytochrome P450 (CYP450) to process and break down a vast number of drugs [1.4.1]. Milk thistle's active components can inhibit or influence some of these enzymes, particularly CYP2C9 and potentially CYP3A4 [1.4.1, 1.5.1].
When milk thistle slows down these enzymes, it can cause certain medications to build up in the bloodstream to potentially toxic levels because they aren't being metabolized at the expected rate [1.5.1]. Conversely, in some situations, it could speed up metabolism, reducing a drug's effectiveness. Data on these interactions can be conflicting, with some studies showing minimal effects while others urge caution [1.4.2, 1.7.7].
Key Drug and Supplement Interactions
It is crucial to consult a healthcare provider before taking milk thistle if you use any of the following medications:
- Diabetes Medications: Milk thistle may lower blood sugar levels. Combining it with diabetes drugs like metformin or insulin could lead to hypoglycemia (dangerously low blood sugar) [1.5.1, 1.6.1].
- Warfarin (Coumadin): As milk thistle may affect the CYP2C9 enzyme that processes this blood thinner, there is a risk of increased bleeding [1.5.1, 1.5.7].
- Statins: There's a theoretical possibility that milk thistle could alter the levels of cholesterol-lowering statins [1.5.7].
- Raloxifene (Evista): Used for osteoporosis, milk thistle may increase the levels of this drug in the bloodstream by affecting how the liver processes it [1.5.1].
- Simeprevir and other Hepatitis C medications: Milk thistle should be avoided with simeprevir as it can increase the drug's plasma concentration [1.5.1]. It may also decrease the effectiveness of sofosbuvir [1.5.7].
- Sirolimus (Rapamune): This immunosuppressant, often used after organ transplants, can be affected by milk thistle, potentially altering its levels [1.5.1, 1.7.7].
- Diazepam (Valium) and other drugs metabolized by CYP2C9: Medications processed by this enzyme, including certain anti-seizure drugs and sedatives, could have altered effects [1.4.1].
- Metronidazole: This antibiotic's serum concentration may be decreased by milk thistle [1.6.7].
Comparison Table: Milk Thistle Interactions
| Drug/Supplement Class | Nature of Potential Interaction | Level of Concern |
|---|---|---|
| Vitamins | No strong evidence of direct contraindication [1.2.2]. | Low |
| Diabetes Medications | Potentiates blood sugar-lowering effect, risk of hypoglycemia [1.5.1]. | High |
| Warfarin (Blood Thinner) | May increase drug levels and risk of bleeding by affecting CYP2C9 [1.5.1, 1.5.7]. | High |
| Raloxifene (Osteoporosis) | May increase drug levels in the bloodstream [1.5.1]. | Moderate to High |
| Simeprevir (Hepatitis C) | Increases plasma concentration of the drug; combination should be avoided [1.5.1]. | High |
| Sirolimus (Immunosuppressant) | May change how the body processes the medication [1.5.1]. | High |
| Statins (Cholesterol) | Theoretical potential to alter drug levels [1.5.7]. | Low to Moderate |
| Estrogen/Hormone Drugs | May have estrogenic effects, affecting hormone levels or drugs [1.5.1, 1.6.1]. | Moderate |
Who Should Avoid Milk Thistle?
Certain individuals should exercise caution or avoid milk thistle altogether:
- Pregnant or Breastfeeding Women: There is insufficient safety data for this group [1.6.2].
- People with Hormone-Sensitive Conditions: Individuals with breast, uterine, or ovarian cancer, as well as endometriosis or uterine fibroids, should avoid milk thistle due to its potential estrogenic effects [1.6.1, 1.6.2].
- Those with Ragweed Allergies: Milk thistle belongs to the Asteraceae plant family, which also includes ragweed, daisies, and marigolds. People allergic to these plants may have an allergic reaction to milk thistle [1.5.1, 1.6.2].
- People with Diabetes: Due to its blood sugar-lowering effects, it should only be used under strict medical supervision [1.6.1].
Conclusion
While the direct question is about vitamins, the more pressing safety concern with milk thistle revolves around its potential interactions with a wide range of medications. There are no vitamins that are strictly forbidden with milk thistle based on current evidence. However, its influence on liver enzymes means it can significantly alter the effectiveness and toxicity of many common drugs. The most prudent course of action is to consult with a doctor or pharmacist before adding milk thistle to your regimen, especially if you are taking any prescription medications or have an underlying health condition.
Find more information at the National Center for Complementary and Integrative Health (NCCIH)
