Milk thistle (Silybum marianum) is a plant native to Europe. For hundreds of years, European herbalists observed that it helped reverse the jaundice that often signals liver damage. Today, milk thistle is sometimes used in the management of liver-related problems. Liver health is an important concern in the management of HIV infection, particularly in people co-infected with viral hepatitis. Unfortunately, milk thistle has not been well studied for these conditions, as most of the studies have involved people with liver damage from alcohol abuse. Recent test-tube studies suggest that milk thistle may be protective of the kidney. Milk thistle may also act as an antioxidant.

Milk thistle is available in health food stores and in drugstores that sell herbal products. Extracts used in clinical trials are standardized to 80 per cent of an active ingredient called silymarin. Milk thistle occasionally has been reported to cause mild diarrhea but has no other reported side effects. It may, however, cause a reaction in people who are allergic to plants from the Asteraceae (daisy) family.

People taking medications, including antiretroviral drugs, should be cautious about the use of milk thistle as it may interact with them. This is because herb-drug interactions can lead to increased side effects or reduced effectiveness of drug therapy (see the section in this guide called Herb-Drug Interactions).