Phentermine
Also known as: Adipex-P, Lomaira, Ionamin, Fastin, Suprenza, Duromine
Lower numbers = closer to natural. Higher numbers = more enhanced.
Why this rating?
Phentermine is a prescription sympathomimetic (a norepinephrine-dopamine releasing agent) that suppresses appetite. It does not build muscle or directly enhance athletic power - its physique effect is indirect, through eating less. As a real pharmaceutical stimulant that drives fat loss beyond what most achieve unaided and is a WADA-prohibited in-competition stimulant, it sits in the same tier as other stimulant fat-burners (ephedrine, tesofensine), but its effect is narrower (appetite only) and clinical weight loss is modest, so it rates 4 rather than higher.
Overview
A prescription appetite-suppressant stimulant approved for short-term treatment of obesity alongside diet and exercise. Structurally an amphetamine relative, it acts as a norepinephrine-dopamine releasing agent (an 'anorectic'). Approved in the US in 1959 and still one of the most prescribed weight-loss drugs, it is meant for short-term use only.
Purpose & Use Cases
Short-Term Appetite Suppression
Reduces hunger to help create a calorie deficit in overweight/obese patients who are also dieting and exercising. FDA-approved for up to 12 weeks of use.
Kickstarting a Diet
Most weight loss occurs in the first weeks, so it is often used to break through the hardest early phase of a low-calorie diet.
Combination Therapy (Qsymia)
Paired with topiramate as the fixed-dose combination phentermine/topiramate (Qsymia) for longer-term chronic weight management.
Benefits
- Effective short-term appetite suppression
- Well-established prescription weight-loss aid (approved since 1959)
- Convenient once-daily oral morning dosing (immediate-release)
- Available as a longer-term combination with topiramate (Qsymia)
- Inexpensive and widely available by prescription
Good to Know
A short-term appetite suppressant, not a fat-burner in the thermogenic sense
Phentermine is an anorectic - it works by decreasing appetite through central norepinephrine-dopamine release, not by cranking up metabolism the way clenbuterol or ephedrine do. FDA-approved since 1959 for short-term use (up to 12 weeks), most weight loss lands in the first weeks and the drug is not meant for open-ended use.
Qsymia is phentermine + topiramate; 'fen-phen' was a different, dangerous combo
The modern combination is phentermine/topiramate (brand Qsymia), used for longer-term weight management. This is not the same as the 1990s 'fen-phen' (phentermine + fenfluramine/dexfenfluramine), which was withdrawn in 1997 over heart-valve damage - the fenfluramine component was the problem, not phentermine.
It is a WADA-prohibited stimulant (in-competition)
Phentermine is a sympathomimetic stimulant closely related to amphetamine. Anti-doping/forensic literature treats it as a monitored substance in athlete urine testing (including a documented case of it appearing as a banned-stimulant positive), and WADA prohibits stimulants in-competition under category S6. It is Schedule IV in the US and can be habit-forming.
Dosage Guidelines
| Experience Level | Dosage Range |
|---|---|
| Beginner | 8 – 18.75 mg/day |
| Intermediate | 18.75 – 37.5 mg/day |
| Advanced | 37.5 – 37.5 mg/day |
Per the Adipex-P (phentermine HCl 37.5mg) FDA label, "the usual adult dose is one capsule (37.5mg) daily," taken before breakfast or 1-2 hours after; some patients do well on a half-tablet (18.75mg) once or twice daily, and the max is capped at 15mg/day in severe renal impairment. Lomaira (8mg tablets) is dosed up to three times daily, 30 minutes before meals. MedlinePlus confirms the single-morning-dose vs. three-times-daily patterns and that it is approved for up to 12 weeks, though most people take it for only 3-6 weeks. Take early in the day to avoid insomnia; late/evening dosing is specifically discouraged on-label. It can be habit-forming (Schedule IV), so do not exceed the prescribed dose or duration. Extended-release/DR capsules should not be split, chewed, or crushed unless the specific product is labeled crushable.
Side Effects
Elevated Heart Rate / Palpitations
commonFast heart beat is a common sympathomimetic effect.
Monitor heart rate; avoid other stimulants; discontinue if palpitations are significant.
High Blood Pressure
commonRaises blood pressure via catecholamine release.
Monitor blood pressure; contraindicated in cardiovascular disease.
Insomnia
commonStimulant-driven trouble sleeping, worse with late dosing.
Dose in the morning only.
Restlessness / Anxiety
commonDizziness, restlessness and jitteriness from CNS stimulation.
Lower dose; avoid combining with other stimulants.
Dependence / Habit Formation
uncommonAs an amphetamine relative and Schedule IV drug, it carries potential for habit formation.
Use short-term only at prescribed doses; do not extend duration.
General Mitigation Strategies
Dose in the morning to limit insomnia and keep it short-term (typically 3-6 weeks, max 12). Contraindicated in cardiovascular disease, hyperthyroidism and glaucoma, during pregnancy, and with MAO inhibitors (per Wikipedia). Monitor blood pressure and heart rate. Do not stack with other stimulants - the cardiovascular strain is additive.
Post Cycle Therapy (PCT)
Not a hormone and does not affect the HPTA. No PCT required.
How It Works
Phentermine is a sympathomimetic that acts primarily as a norepinephrine-dopamine releasing agent. The resulting central catecholamine surge suppresses appetite (and produces classic stimulant effects). Wikipedia and MedlinePlus classify it as an anorectic - it works by decreasing appetite rather than by boosting metabolism the way thermogenic beta-agonists do.
Fundamentals
Reference on the practices relevant to Phentermine: how they are done and where they go wrong. Not a recommendation to use it.
Legal Status
Schedule IV controlled substance (USA); prescription-only.
Legal status varies by country and changes over time. This is a general summary, not legal advice.
WADA Status
Phentermine is a sympathomimetic stimulant, pharmacologically related to amphetamine. Wikipedia does not itself address WADA, but anti-doping/forensic literature treats it as a monitored stimulant: a doping-control pharmacokinetics study examined how diuretics alter its urinary excretion/detectability (PMID 3954816), and a documented athlete anti-doping case shows phentermine turning up as a banned stimulant in urine, in that instance from an oxethazaine-containing antacid metabolizing into it (PMID 19157735). WADA prohibits stimulants in-competition under category S6, so it is treated here as prohibited in-competition and permitted out-of-competition, consistent with how other norepinephrine-releasing anorectics (e.g. phendimetrazine) are classified. Confirm current WADA Prohibited List/Global DRO listing before competing.
References
- Phentermine - Wikipedia
- Phentermine - MedlinePlus
- Adipex-P (phentermine hydrochloride) prescribing information - RxList
- Delbeke & Debackere 1986 - phentermine urinary excretion & diuretic masking in doping control (PMID 3954816)
- Hsu et al. 2009 - phentermine as a banned stimulant / false-positive source in athlete doping control (PMID 19157735)