Does drinking alcohol on the day of Picosure treatment cause side effects?

It may affect how much you bruise. If you have not yet had your PicoSure treatment then I would advise you to avoid alcohol for a least 2 days prior to treatment. If you've already had it, I guess you'll see whether or not it bothers you. My best, Dr. Sheila Nazarian @drsheilanazarian on Instagram

In general, I recommend that alcohol be avoided around the time of surgery.  Alcohol, particularly in higher amounts can impair platelet function or clotting factors leading to increased bruising or bleeding.  If you are asking this question before your treatment I'd steer clear of alcohol for a few days to be safest or at least limit it (e.g. a glass of wine).  If you are asking this question after the treatment, not much to do other than observe to see if more bruising than expected.