People have taken milk thistle (silybum marianum) for liver disorders, such as hepatitis and cirrhosis, since the days of the Ancient Greeks. The main active ingredient is an antioxidant called silybin.
Robust clinical evidence for its supposed effects is still lacking, but small-scale lab studies suggest that silybin may help to protect the liver from alcohol damage by, for instance, reducing the effect of damaging molecules called ‘reactive oxygen species’, levels of which are boosted by alcohol.
However, none of these studies supports the idea that silybin can help with a hangover, which involves different biological processes. When you drink, enzymes in your body first convert the alcohol into a toxic, carcinogenic chemical called acetaldehyde. An enzyme called aldehyde dehydrogenase then converts acetaldehyde into acetate, which can break down to form water and carbon dioxide.
But if you’ve consumed excessive alcohol, acetaldehyde builds up because there’s not enough enzyme to deal with it. This increase in toxic chemicals is a major contributor to the nausea and headaches you feel the morning after.
There is, however, no evidence that milk thistle can reduce acetaldehyde levels, and there’s no magic way to avoid a hangover. Just make sure you eat before hitting the alcohol and drink plenty of water before you go to bed.