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Many compounds have a tricyclic structure, but in pharmacology, the term has traditionally been reserved to describe heterocyclic drugs. Among these are antidepressants, antipsychotics, anticonvulsants, and antihistamines (as antiallergens, anti-motion sickness drugs, antipruritics, and hypnotics/sedatives) of the dibenzazepine, dibenzocycloheptene, dibenzothiazepine, dibenzothiepin, phenothiazine, and thioxanthene chemical classes, and others.
- Promethazine and other first generation antihistamines with a tricyclic structure were discovered in the 1940s.
- Chlorpromazine, derived from promethazine originally as a sedative, was found to have neuroleptic properties in the early 1950s, and was the first typical antipsychotic.
- Imipramine, originally investigated as an antipsychotic, was discovered in the early 1950s, and was the first tricyclic antidepressant.
- Carbamazepine was discovered in 1953, and was subsequently introduced as an anticonvulsant in 1965.
- Antidepressants with a tetracyclic structure such as mianserin and maprotiline were first developed in the 1970s as tetracyclic antidepressants.
- Clozapine was introduced as the first atypical antipsychotic in the 1990s.
- Loratadine was introduced as a non-sedating second generation antihistamine in the 1990s.