It is safe. But you should consider some things:
SSRIs like Cymbalta generally make the effects of serotonergic drugs like psychedelics and MDMA much weaker in effect. Some people report relatively unchanged trips, but it seems that most report never being able to really full-on trip while on SSRIs.
Benzodiazepines like clonazepam/Klonopin mute the effects of psychedelics. They bring the trip down because of how they work in the brain. It's definitely still possible to trip on them, but they're one of the most commonly used drugs to use to help someone come down from a negative experience if they choose to abort it.
Finally, SSRIs mess with the serotonin system in your brain in a pretty serious manner... since psychedelics work on the serotonin system, it's kind of a minefield to walk into to be honest. I wouldn't take psychedelics while on SSRIs just because we don't really have any idea how they could interact since very few studies are being done on psychedelics. Even though plenty of people do and it doesn't SEEM to be dangerous (just inefficient), I still wouldn't do it just on principle. Because really, you're probably on SSRIs for a reason. If you don't really feel you need them it would really be best to talk with your doctor and work on getting off of them because they're not harmless, and then you can trip after you get off of them for a more full experience. But if you're on them for a good reason, you really shouldn't be tripping until you deal with that anyway, IMO.
