I personally just got off lexapro a few weeks ago, thank god. I wish I had known of the long term effects and exactly how most SSRI's work before I got on that poison.. anyway, I've drank many times and smoked bud with no problems whatsoever. Took many opiates while on lexapro and a number of psychedelics (shrooms, DOx, 2Cx, salvia, LSD, NBOME) all with no problems either. The only thing I noticed with tripping was slightly weakened effects, which were easily solved by increasing the dose.. I've only taken lexapro but from what I hear it's one of the more "mild" SSRI's compared to effexor and others. And With little drug interactions..
Excuse me getting off topic, it appears that alcohol is just fine while on lexapro. But like anything, you don't wanna over do it as habitual drinking (depressant) will probably counteract antidepressants' effects. So keep that in mind and use in moderation.