It can be, yes. Psychedelics themselves are harmless, wonderful medicine, not drugs, but please do not mix them with SSRIs. And don’t take heroic doses or combine different drugs without first checking the combination safety. There is such a thing as serotonin syndrome, although it happens extremely rarely. That’s pretty much the only danger.

Most psychedelics, at least the classical ones, such as LSD and magic mushrooms, are incapable of inducing serotonin syndrome by themselves, it’s not a possibility. They are physically safe, non-addictive, and it’s not possible to overdose on them. They are safe. Just take it slow, because the higher the dose the more challenging the experience will be. But high doses combined with SSRIs or MDMA make serotonin syndrome a very remote possibility, it has been documented. If you want to experiment with psychedelics, it’s best to wean yourself off SSRIs first. It’s probably not too dangerous, and people do it all the time, but better safe than sorry. They are much better treatment for depression anyway.

Research safety and dosage before using them and check this for combinations: Drug combinations

Better yet, stick with just one, such as LSD or magic mushrooms, because it’s not about the experience, but the changes in your perception of life afterwards.