Phentermine
| Category | Compounds |
|---|---|
| Also known as | Adipex-P, Lomaira, α-Methylamphetamine Derivative |
| Last updated | 2026-04-14 |
| Reading time | 3 min read |
| Tags | weight-losssympathomimeticappetite-suppressantsmall-moleculeresearch |
Overview
Phentermine is a sympathomimetic amine that has been used as a short-term appetite suppressant for obesity since the late 1950s. Structurally related to amphetamine but with a modified side chain that blunts central stimulant potency, it remains one of the most widely prescribed small-molecule weight-loss drugs worldwide. A fixed-dose combination with topiramate (Qsymia) is also approved for longer-term weight management.
Although phentermine is not a peptide, it is routinely catalogued in peptide and metabolic research references because it is frequently compared to peptide-based weight-loss agents including Semaglutide, Tirzepatide, Cagrilintide, Tesofensine, and the research peptide Adipotide. It is also discussed alongside the melanocortin agent Setmelanotide in obesity pharmacotherapy reviews.
Phentermine's long regulatory history — including the notable 1997 withdrawal of its companion drug fenfluramine (of "fen-phen" infamy) due to cardiac valve concerns — makes it a useful reference point for evaluating newer weight-loss pharmacotherapy.
Structure / Chemistry
Phentermine is α,α-dimethylphenethylamine (molecular formula C10H15N, MW ~149 g/mol). The additional methyl group relative to amphetamine reduces central stimulant activity while preserving anorexigenic potency.
Mechanism of Action
Phentermine stimulates release of norepinephrine (and, at higher doses, dopamine and serotonin) from presynaptic terminals. Elevated noradrenergic tone in hypothalamic appetite centers suppresses hunger and increases satiety. Effects on peripheral adrenergic receptors contribute to modest increases in heart rate and blood pressure that shape its clinical risk profile.
Research Summary
| Area | Finding | Reference |
|---|---|---|
| Short-term weight loss | Modest weight reductions over 12 weeks | Munro et al., BMJ 1968 |
| Combination | Phentermine/topiramate CONQUER trial | Gadde et al., Lancet 2011 |
| Cardiovascular | Blood pressure and heart rate monitoring needs | Multiple post-marketing analyses |
| Pharmacology | Noradrenergic release and hypothalamic effects | Bray et al., Obes Res 2005 |
| Long-term use | Extended-use observational outcomes | Hendricks et al., Obesity 2014 |
Pharmacokinetics
Phentermine is orally bioavailable with a plasma half-life of approximately 20 hours, supporting once-daily dosing. It is primarily excreted unchanged in urine. Clinical doses range from 15 to 37.5 mg daily; specific doses are referenced as clinical trial parameters and not medical guidance.
Common Discussion Topics
- Historical context of "fen-phen" and fenfluramine withdrawal.
- Short-term vs. long-term use regulatory distinctions.
- Comparison with GLP-1 agonists on efficacy and side-effect profile.
- Cardiovascular monitoring and contraindications.
- Combination therapy with topiramate (Qsymia).
Related Compounds
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Related entries
- Adipotide— Adipotide is a proapoptotic peptide designed to target adipose-tissue vasculature, studied in preclinical obesity models for adipose-specific fat reduction.
- Cagrilintide— Cagrilintide is a long-acting amylin analog investigated for weight management, often studied in combination with GLP-1 receptor agonists.
- Semaglutide— A long-acting GLP-1 receptor agonist approved for type 2 diabetes (Ozempic) and chronic weight management (Wegovy), with emerging cardiovascular, renal, and neurological research applications.
- Setmelanotide— A synthetic cyclic octapeptide melanocortin 4 receptor agonist, setmelanotide is an FDA-approved treatment for chronic weight management in patients with obesity due to specific monogenic defects in the leptin-melanocortin signaling pathway, including POMC, PCSK1, and LEPR deficiency.
- Tesofensine— Tesofensine is a triple monoamine reuptake inhibitor studied for appetite suppression and weight loss, originally investigated for neurodegenerative disease.