It depends on the antidepressant. With trazadone i took it for sleep for a while and found that like you'd expect it increased the drowsiness/relaxation but didn't make the high more intense. SSRIs can be a crapshoot whether they diminish or enhance the high or have other weird effects. Buproprion, an NDRI, greatly increases the high from weed (and the effects of most drugs) for me. As someone who was previously a daily smoker I could get sufficiently high off one or two bowls out of a bong where it'd normally take me five or six. Now I took a tolerance break too so I can't know for certain what caused what, but my tolerance hasn't changed at all, and other people who have taken it say the same thing, it makes weed more intense. Trazodone though, ime, doesn't really affect the "high" it just makes you tired, a bit more relaxed, and may kill some of the anxiety/paranoia but it's not as good as a benzo or a barb or even alc at doing that.
