According to the Alli website, it's safe to drink alcohol when taking Alli.
An older study in 30 people found that taking orlistat with 40 grams of alcohol, which equates to approximately 3 glasses of wine, did not result in adverse side effects or change the way orlistat worked in the body (21).
However, even though a moderate amount of alcohol is safe to consume when taking Alli, it's important to understand that consuming too much alcohol can negatively impact health in a number of ways and can even make it harder for you to lose weight (22).