Milk thistle seed may cause allergic reactions in those sensitive to ragweed, marigold, or other Asteraceae plants. It can interact with medications processed by the liver, including blood thinners, statins, diabetes drugs, and hormone therapies, potentially altering their effectiveness. Pregnant or breastfeeding individuals should avoid use due to limited safety data, and those with hormone‑sensitive conditions (such as certain cancers or endometriosis) should exercise caution. Mild digestive side effects like bloating, diarrhea, or nausea are also possible.