Trazodone (Trittico)

Trazodone (brand names include Trittico, Desyrel, Oleptro) is a triazolopyridine derivative and the prototype of the SARI class - serotonin antagonist and reuptake inhibitor. It has been clinically approved since the 1970s and is among the oldest antidepressants still in wide use.

What makes trazodone interesting, though, is something else: it is one of the cleanest textbook examples of a molecule having two completely different effect profiles depending on dose. That is not a detail, it is the central point in understanding this substance.

This information is for research and educational purposes only. No medical advice.

Trazodone engages several receptors at once, with very different binding strengths:

• 5-HT2A antagonism: very strong binding. Blocking this receptor is closely linked to slow wave sleep promotion and sedation.
• H1 antagonism: strong binding at the histamine receptor. The same mechanism that makes classic antihistamines drowsy.
• Alpha-1 blockade: strong binding at the adrenoceptor. Responsible for the blood pressure drop on standing - and for priapism.
• 5-HT2C antagonism: moderate binding, also contributes to the sleep profile.
• SERT inhibition: comparatively weak binding at the serotonin transporter. This is the antidepressant mechanism - and the one that needs the most dose.

Breakdown runs primarily through CYP3A4 and generates the active metabolite mCPP (meta-chlorophenylpiperazine), which is serotonergically active itself and can accumulate when CYP3A4 is inhibited.

Because affinity for 5-HT2A and H1 is many times higher than for the serotonin transporter, the receptors fill in a fixed order. That creates two separate dose windows:

• 25 to 100mg: practically only 5-HT2A, H1 and alpha-1 are occupied. The serotonin transporter is barely engaged. Result: pronounced sedation, no meaningful serotonergic effect.
• from about 150mg: SERT inhibition now reaches a level that studies link to antidepressant action. The serotonergic component is added, but the pure sedation does not get stronger.

Stahl described this model in detail in 2009. The practical consequence is often missed: a low dose is not a weaker version of a high dose, it is pharmacologically something else. Titrating up for more sedation does not deliver more sedation, it pushes the compound into a different profile with a different side effect picture.

• Bioavailability: roughly 65 to 80 percent oral.
• Onset: peak concentration about one hour after a fasted dose. With food, delayed to around two hours, but with a flatter peak and less dizziness.
• Half-life: biphasic - first phase about 3 to 6 hours, terminal phase roughly 5 to 9 hours.
• Metabolism: primarily CYP3A4, active metabolite mCPP.

The short first phase explains why trazodone is given in the evening at low doses. The terminal phase explains why carryover can still be measurable the next morning.

Roth et al. (Journal of Sleep Research 2011) studied 50mg over seven days randomized, double-blind and placebo-controlled in 16 people with primary insomnia. Under trazodone there were fewer nighttime awakenings, less stage 1 sleep and more slow wave sleep on day seven. At the same time there were measurable decrements in short-term memory, verbal learning, equilibrium and muscle endurance the following morning. Both findings belong together.

Fagiolini et al. (CNS Drugs 2012) classified trazodone as an antidepressant with efficacy comparable to SSRIs, SNRIs and tricyclics, with the difference that the typical SSRI-related sleep disruption does not appear.

Mendelson (Journal of Clinical Psychiatry 2005) reviewed 18 papers on sleep use and reached a deliberately critical conclusion that the evidence is limited: most studies are small, were collected in depressed populations and often work without objective measures. The Lancet network meta-analysis by De Crescenzo et al. (2022) across 170 trials confirms this and lists trazodone among the substances effective in acute use but with limited tolerability or long-term data.

Honest classification: the sedation is undisputed and pharmacologically well explained. The quality of the sleep studies is not.

• Priapism: the classic rare but serious adverse effect, caused by alpha-1 blockade in the corpus cavernosum. Occurs at low doses too. A painful erection lasting several hours without sexual stimulus is a urological emergency - delayed treatment is linked in the literature to permanent erectile impairment. A rare female counterpart has also been reported.
• Serotonin syndrome: risk on combination with MAO inhibitors, SSRIs, SNRIs, triptans, linezolid, tramadol or St John's wort. The metabolite mCPP adds to the serotonergic load. Signs: agitation, tremor, muscle twitching, hyperreflexia, sweating, rising temperature.
• Orthostatic hypotension: blood pressure drop on standing, with fall risk especially at night and in older individuals.
• Next-day carryover: sedation, dizziness and psychomotor decrements are documented. Driving ability can still be impaired in the morning.
• QT prolongation: documented, with torsade de pointes in isolated cases. Relevant with heart disease, electrolyte disturbance or other QT-prolonging substances.
• CYP3A4 interaction: strong inhibitors (ketoconazole, itraconazole, ritonavir, clarithromycin) markedly raise levels, inducers such as carbamazepine lower them.
• Tolerance and discontinuation: evidence of tolerance development with longer use. Do not stop abruptly, taper instead - rebound insomnia is described.

Unlike the tricyclics, trazodone has practically no anticholinergic activity, so the dry mouth and urinary retention profile largely does not apply.

Store dry, at room temperature and protected from light. Keep tablets in the original packaging. Out of reach of children.