Phenethylhydrazines

Phenelzine, sold under the brand name Nardil among others, is a non-selective and irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine family which is primarily used as an antidepressant and anxiolytic to treat depression and anxiety. Along with tranylcypromine and isocarboxazid, phenelzine is one of the few non-selective and irreversible MAOIs still in widespread clinical use.

Carbidopa, sold under the brand name Lodosyn, is a medication used primarily in the treatment of Parkinson's disease. It is a DOPA decarboxylase inhibitor — that is, it blocks the enzyme aromatic L-amino acid decarboxylase (DDC) in the peripheral nervous system, preventing the premature conversion of levodopa to dopamine outside the brain. Because carbidopa cannot cross the blood-brain barrier, it has no effect on DDC activity within the central nervous system, allowing a greater proportion of co-administered levodopa to reach the brain intact.

Pheniprazine, formerly sold under the brand names Catron and Cavodil, is an irreversible and non-selective monoamine oxidase inhibitor (MAOI) of the hydrazine group that was used as an antidepressant to treat depression in the 1960s. It was also used in the treatment of angina pectoris and schizophrenia. Pheniprazine has been largely discontinued due to toxicity concerns such as jaundice, amblyopia, and optic neuritis.

Metfendrazine (developmental code names HM-11, MO-482), also known as methphendrazine, is an irreversible and nonselective monoamine oxidase inhibitor (MAOI) of the hydrazine family. It was investigated as an antidepressant, but was never marketed.