Trazodone

Atypical sedating antidepressant whose off-label use for insomnia (US) outpaces its on-label antidepressant use — primary care's go-to "non-controlled, non-addictive sleep alternative to Ambien." Dose-split pharmacology: 25-100 mg pre-bed drives sedation via 5-HT2A + H1 + α1 blockade (substantially below the threshold where serotonin reuptake inhibition kicks in); 150-600 mg reaches SERT saturation for the antidepressant indication. For Dylan: SKIP-FOR-NOW. He has no depression, no insomnia (he has a chronotype problem), and his V4/V5 stack already covers sleep with cleaner tools (l-tryptophan + magnesium + l-theanine + apigenin; daridorexant on WATCH-LIST as escalation). Trazodone is "modestly better than Z-drugs" — true on dependence/abuse — but daridorexant is meaningfully better than both on architecture, next-day cognition, side-effect cleanliness, and lacks the priapism and QTc risks that come standard with trazodone.

Trazodone is a triazolopyridine structurally distinct from SSRIs, TCAs, and SNRIs. The drug class label "SARI" — Serotonin Antagonist and Reuptake Inhibitor — was essentially coined to describe trazodone (and later nefazodone) because its receptor pharmacology doesn't fit the older categories.

Receptor binding profile (Ki, nM — lower = stronger affinity):

• 5-HT2A antagonist — Ki ~13-35 nM. Dominant pharmacology at low doses. Roughly half of brain 5-HT2A receptors are blocked at 1 mg trazodone; essentially all are saturated at ~10 mg. This means every clinical sleep dose (25-100 mg) is fully saturating 5-HT2A, and any further dose escalation adds nothing on this receptor — only adds the other receptors below.
• H1 (histamine) antagonist — strong. Drives the antihistaminergic sedation common to TCAs, mirtazapine, doxepin, diphenhydramine. This is the "weighted eyelids" feel.
• α1-adrenergic antagonist — strong. Blocks the sympathetic-tone receptor in vasculature and sympathetic outflow → orthostatic hypotension + dizziness on standing + relaxed peripheral vasodilation (the mechanism of trazodone-induced priapism). Also contributes to sedation centrally.
• 5-HT2C antagonist — moderate (~15× weaker than 5-HT2A). At sleep doses contributes mildly; at antidepressant doses more relevant.
• 5-HT2B antagonist — moderate. Cardiac valve safety (no fenfluramine-style risk).
• SERT (serotonin transporter) inhibitor — weak. Trazodone is a very weak SRI — only at saturating antidepressant doses (150-600 mg) does SERT occupancy approach SSRI-level inhibition. At 25-100 mg sleep doses, the SERT effect is essentially absent. This is the key insight: low-dose trazodone is mechanistically a 5-HT2A/H1/α1 sedative, NOT a serotonergic antidepressant.

Active metabolite — m-chlorophenylpiperazine (m-CPP).

• Generated by CYP3A4 N-dealkylation of trazodone in the liver.
• m-CPP is a 5-HT2C agonist (and weak 5-HT1B/1A agonist) — the opposite direction from the parent drug at 5-HT2C, and it crosses the BBB.
• m-CPP is anxiogenic in healthy volunteers and panic-disorder patients at experimental challenge doses; in trazodone-treated patients it accumulates at low concentrations relative to parent drug, but in CYP2D6 poor metabolizers (PMs) it accumulates more (CYP2D6 hydroxylates m-CPP for clearance). This is the mechanism behind reports of paradoxical anxiety, jitteriness, dizziness, or "weird vibe" in a subset of trazodone users — particularly first-dose. Dylan's pending 23andMe data (June 2026) will tell whether he's CYP2D6 PM (~7-10% in Caucasians).
• The m-CPP profile is also why trazodone shouldn't be combined with serotonergic agents that further raise 5-HT2C signal (MAOIs absolute contra; SSRIs caution).

Half-life: ~3-9 hours (typically cited as 5-9 hr, biphasic α/β phases). Short relative to most psychotropics — this is why trazodone "works for sleep but doesn't always last the night" at sleep doses. It's also why next-morning hangover is dose-dependent: at 50 mg most people clear; at 100-150 mg residual into morning is common. Extended-release formulations (Oleptro, now generic) flatten the curve for antidepressant dosing but are not used for insomnia.

Why is the dose split so dramatic?

The "low dose for sleep / high dose for depression" pattern is not arbitrary marketing — it's pharmacodynamic. SERT requires sustained high plasma concentrations to occupy >70% of transporter (the threshold for antidepressant efficacy across SSRIs). Trazodone's affinity for SERT is weak enough that 25-100 mg gets nowhere near SERT saturation, while the same dose already fully saturates 5-HT2A (~10 mg saturation point). The 5-HT2A blockade plus H1+α1 blockade is sufficient for sedation; the SRI activity that would also produce mood lift simply isn't there at low doses. At 150-600 mg you cross the SERT saturation threshold and pick up the antidepressant effect — but also pick up much heavier sedation, more orthostatic hypotension, more priapism risk, and full hangover-grade morning residual.

This is why prescribers have effectively created a separate "low-dose trazodone hypnotic" practice that isn't reflected in any FDA label (insomnia is NOT an approved indication anywhere, despite ~50% of all trazodone prescriptions being for sleep).