Tricyclic antidepressant (sedating tertiary amine)

Plain-language summaryIntrigue 50 / 100

Trimipramine (Surmontil) is the odd duck of the tricyclic family. A single methyl group on the side chain disrupts its ability to block the serotonin and norepinephrine pumps, so it does almost none of the standard tricyclic action. Instead its effects come from heavy histamine receptor blockade plus blocking a basket of serotonin, alpha-1, and dopamine receptors. The result is a strongly sedating drug used mainly for depression with prominent insomnia. It is one of the few antidepressants that does not suppress REM sleep. Approved by the FDA in 1979, it remains in use mostly in Europe. The mechanism is interesting precisely because it shows that an antidepressant does not necessarily need monoamine reuptake inhibition to work. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Our opinion on this compoundEstablished workhorse

44/100

Unusual non-transporter TCA with narrow but genuine probe value for mechanism dissection

Look, trimipramine is genuinely unusual among TCAs, and thats actually the only reason it earns a spot in a serious research library at all. Most tricyclics work by hammering SERT and NET: imipramine, amitriptyline, nortriptyline, all of them. Trimipramine does something different. SERT Ki sits around 150 nM and NET Ki is an almost useless 2400 nM, which means the monoamine transporter story basically drops out. What’s left is extremely potent H1 antagonism (Ki ~0.27 nM, comparable to first-generation antihistamines), strong 5-HT2A and alpha-1 blockade, and meaningful D2 antagonism. That pharmacological profile makes it an interesting tool for one specific job: dissecting what TCAs actually do when you remove the transporter component.

We think the bench utility here is real but narrow. If you’re investigating whether TCA antidepressant effects are truly transporter-dependent, or you want to understand the separate contributions of H1 and D2 blockade to sedation, sleep architecture, or antipsychotic-adjacent activity, trimipramine is a legitimate reference point. Riemann et al. in the early 1990s showed it preserved slow-wave sleep without the REM suppression typical of SERT-active TCAs, which is genuinely interesting and hasn’t been replicated often enough. That’s the kind of signal worth chasing if sleep architecture is your question.

What we don’t like: this is a 1979 FDA approval with a mechanism that’s been understood for decades. The H1 story isn’t new. D2 antagonism isn’t new. The weak-transporter TCA angle is a curiosity more than a frontier. There’s no recent surge of interest, no emerging indication that elevates it, and the clinical literature is thin compared to amitriptyline or nortriptyline. The depression and insomnia data mostly predates modern trial standards, and we’re not aware of serious ongoing programs studying it in genuinely novel contexts.

The differentiation story is honestly pretty weak outside that specific probe application. For sedation research you’d compare against doxepin (similarly potent H1, more evidence in primary insomnia), quetiapine (D2 and H1 profile backed by a much larger evidence base), or mirtazapine (cleaner H1 with better tolerability data across modern trials). Trimipramine doesn’t dominate any of those comparisons except in the non-transporter TCA niche. The pharmacokinetics are also messy: half-life spans 16 to 40 hours and CYP2D6, CYP2C19, and CYP3A4 all participate, which complicates clean interpretation in multi-compound bench work.

Honestly, if your research question is specifically what TCA pharmacology looks like without the transporter contribution, trimipramine is your molecule. That’s a real question with real mechanistic weight. But if you’re casting wider, there are better targets at almost every other point in this space. The score reflects both the genuine probe utility and the limited scope of that utility.

Novelty: 20
Mechanism promise: 40
In-category differentiation: 42
Evidence quality: 60
Translational signal: 58
Research bench value: 55

Rationale Trimipramine’s methyl substitution almost abolishes SERT and NET activity, leaving an unusually pure H1/D2/5-HT2A antagonism profile that gives it real but narrow utility as a reference probe for dissecting non-transporter TCA effects. Low novelty as a 1979 approval with fully understood pharmacology anchors the score; bench value for specific mechanistic questions provides the floor.

Tricyclic antidepressant (sedating tertiary amine)

A sedating tertiary amine TCA with weak SERT and NET activity; the principal effect is dopaminergic and antihistaminergic.

Abstract

Trimipramine (3-(10,11-dihydro-5H-dibenzo[b,f]azepin-5-yl)-N,N,2-trimethylpropan-1-amine; CAS 739-71-9; molecular formula C20H26N2; molecular weight 294.43) is a 2-methylated dibenzazepine TCA approved by the FDA in 1979 under the trade name Surmontil. The methyl substitution at the propanamine’s beta carbon disrupts transporter binding: SERT Ki approximately 150 nM, NET Ki approximately 2400 nM, both several orders of magnitude weaker than amitriptyline or imipramine. The therapeutic effect is therefore primarily attributed to potent H1 (Ki approximately 0.27 nM, comparable to first-generation antihistamines), 5-HT2A, alpha-1, and D2 antagonism. The compound is among the most sedating TCAs in clinical use and is used preferentially in depression with severe insomnia. Plasma half-life is 16 to 40 hours; metabolism is via CYP2D6, CYP2C19, CYP3A4. Used as a reference compound for non-transporter TCA mechanism research; the H1 and dopaminergic profiles distinguish it from typical TCA pharmacology.

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Tag: Tricyclic antidepressant (sedating tertiary amine)

Trimipramine

Abstract

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