The hydrazine antidepressants are a group of non-selective, irreversible monoamine oxidase inhibitors (MAOIs) which were discovered and initially marketed in the 1950s and 1960s. Most have been withdrawn due to toxicity, namely hepatotoxicity, but a few still remain in clinical use.
Tranylcypromine, a structurally unrelated MAOI introduced around the same time as the hydrazines, was originally advertised as non-hydrazine as a result of its diminished propensity for causing hepatotoxicity.