Trazodone hydrochloride is a prescription antidepressant, first approved by the FDA in 1981. It belongs to a small class of medications called serotonin antagonists and reuptake inhibitors (SARIs) — a category defined largely by trazodone itself, since it's the most widely prescribed drug in this group.
Trazodone was developed as an alternative to older tricyclic antidepressants, aiming to treat depression with less of the anticholinergic and cardiac burden those older drugs carried. It succeeded on that front, but it turned out to have a strong sedative side effect — which is exactly why, decades later, it's now prescribed far more often off-label for sleep than on-label for depression.
Today, trazodone is available only as a generic medication (the original brand, Desyrel, is no longer marketed), and it's one of the most commonly prescribed medications in the United States overall, spanning both its approved use and its off-label popularity.