RESEARCH MONOGRAPH · KDC-MN-072

Agomelatine

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

63/100

Clever dual-mechanism antidepressant whose modest effect size and hepatotoxicity signal kept it from becoming a workhorse

Agomelatine is one of those drugs where the medicinal chemistry is more elegant than the clinical reality. Servier designed it (again, Servier, they had a good decade for atypical antidepressants) as a melatonergic naphthalene analog with the dual rationale of restoring circadian rhythm and indirectly modulating monoamines through 5-HT2C antagonism. The MT1/MT2 agonism plus 5-HT2C antagonism combination is unusual and the dis-inhibition of frontocortical dopamine and norepinephrine via 5-HT2C blockade is a legitimate mechanism.

What we like: the chronobiology angle is genuinely interesting. Most antidepressants don't address circadian disruption, which is one of the most reliable biomarkers of depression. Agomelatine resynchronizes sleep architecture and improves slow-wave sleep in a way SSRIs generally don't. For studying melatonin-receptor pharmacology in mood-related circuits, it's a useful tool compound, and the synthetic chemistry is reasonably accessible.

What we dont like: the actual clinical effect size is modest. Multiple meta-analyses (Taylor 2014, Guaiana 2013, the Cochrane review) put agomelatine at roughly equivalent or slightly inferior to standard SSRIs, with the main advantages being better sleep quality and less sexual side-effect burden. Those are real but they didn't add up to the breakout drug Servier wanted.

The hepatotoxicity signal is the bigger issue. About 1.5% of patients show transaminase elevations and there have been case reports of severe hepatic injury. The EMA mandates liver function monitoring at 3, 6, 12, and 24 weeks for clinical prescribing, which tells you the pharmacovigilance signal is real even if the absolute risk is small.

Sourcing-wise, the naphthalene synthesis is standard and HPLC pure material is achievable. Most research-grade vendors handle this one fine, just verify the chromatograms because there are some Indian generics floating around with variable impurity profiles.

For melatonergic mood-circuit pharmacology research, agomelatine has a place. As a generic interesting antidepressant, the data didn't justify the hype. The mechanism is more compelling than the outcomes.

Evidence: 65
Mechanism: 78
Reliability: 60
Safety: 55
Sourcing: 75
Value: 60
Signal: 55
Staying power: 55

Plain-language summary Intrigue 68 / 100

Agomelatine is an antidepressant that combines melatonin receptor activation (sleep regulation) with 5-HT2C antagonism (mood). FDA declined approval; widely used in Europe under the brand Valdoxan. 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.

Melatonin receptor agonist + 5-HT2C antagonist

A Servier-developed antidepressant approved in Europe combining MT1/MT2 melatonin receptor agonism with 5-HT2C antagonism, characterized by hepatotoxicity monitoring requirement.

Abstract

Agomelatine (Valdoxan, Thymanax; S-20098; CAS 138112-76-2; molecular formula C15H17NO2; molecular weight 243.30) is a structural analog of melatonin developed by Servier and approved by the EMA in 2009 for major depressive disorder. The compound combines MT1 and MT2 melatonin receptor agonism (similar potency to endogenous melatonin) with 5-HT2C receptor antagonism. The melatonin agonism provides a circadian-resynchronizing effect that may underlie sleep architecture improvements; the 5-HT2C antagonism increases dopamine and norepinephrine release in frontal cortex, providing the antidepressant component of activity. The compound does not increase serotonin transmission and does not produce the typical SSRI/SNRI adverse event profile. Pharmacokinetics: plasma half-life 1 to 2 hours; high oral bioavailability with substantial first-pass metabolism via CYP1A2. Reported research dose ranges in the literature are described in the source monograph. Hepatotoxicity is the principal safety concern; baseline and periodic ALT monitoring is required.

Mechanism of action

MT1/MT2 melatonin receptor agonist + 5-HT2C antagonist. Circadian resynchronization plus DA/NE elevation in PFC.

Reported research dose ranges

25 to 50 mg.

References

Kennedy SH, Rizvi SJ. Agomelatine in the treatment of major depressive disorder: potential for clinical effectiveness. CNS Drugs 2010.

Read the full monograph

The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, reported research dose ranges, sourcing and quality verification, reconstitution and handling, stack interaction considerations, and a curated reference list. Available as a research-use-only PDF download.

KDC-MN-073

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

Kodiac sells research compounds for investigative use only.

Agomelatine

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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