If you are currently being treated with any of the following medications, you should not use milk thistle without first talking to your healthcare provider.

Similar to its ability to protect against damage to the liver from alcohol and acetominophen, as discussed in the Overview, milk thistle may also protect against liver damage from the following medications:

• Antipsychotics: This group of medications used for schizophrenia includes butyrophenones (such as haloperidol) and phenothiazines (such as chlorpromazine, fluphenazine, and promethazine)
• Phenytoin: a medication used for seizures
• Halothane: a medication used during general anesthesia

Other medications that may interact with milk thistle include:

Aspirin
One animal study found that milk thistle may enhance the effectiveness of aspirin in rats with liver cirrhosis. Whether this herb-drug combination has the same effect in people is not known at this time.

Chemotherapy medications
Preliminary research suggests that silybin may enhance the tumor fighting effects of cisplatin and doxorubicin when tested against breast and ovarian cancer cells.

In addition, milk thistle may protect the kidneys against toxic side effects associated with cisplatin and cyclosporine, two medications that are commonly used to treat cancer.

On the other hand, a different laboratory study revealed that the anticancer effect of cisplatin and ifosfamide was diminished in the presence of milk thistle. More research needs to be done to assess how milk thistle and cancer-fighting agents interact.