Pharmacology: Inhibits reuptake of serotonin, causes adrenoreceptor subsensitivity, acts as a 5HT2a receptor antagonist and induces significant changes in 5-HT presynaptic receptor adrenoreceptors. Trazodone also significantly blocks histamine (H1) and alpha1-adrenergic receptors.
Insomnia (off-label use): Oral: Immediate release: Usual dose: 50 mg to 100 mg at bedtime (Kaynak 2004; Roth 2011; Walsh 1998). Doses up to 600 mg have been evaluated in patients with insomnia associated with depression (typical ranges of 50 to 300 mg); however, the quality of the evidence precludes definitive conclusions of efficacy (Mendelson 2005; Sateia 2017). Additional data may be necessary to further define the role of trazodone in this condition.
Simple Summary: Mechanism of Action--> Trazodone blocks H1 receptors. By blocking those receptors the effect is (usually) drowsiness.
Kaynak H, Kaynak D, Gözükirmizi E, Guilleminault C. The effects of trazodone on sleep in patients treated with stimulant antidepressants. Sleep Med. 2004;5(1):15-20.[PubMed 14725822]
Roth AJ, Mc Call WV, Liguori A. Cognitive, psychomotor and polysomnographic effects of trazodone in primary insomniacs. J Sleep Res. 2011;20(4):552-558.[PubMed 21623982]
Walsh JK, Erman M, Erwin CW, et al. Subjective hypnotic efficacy of trazodone and zolpidem in DSMIII-R primary insomnia. Human Psychopharmacology. 1998:13;191-198.
Mendelson WH. A review of the evidence for the efficacy and safety of trazodone in insomnia. J Clin Psych. 2005;66(4):469-476.[PubMed 15816789]