Short answer: Phendimetrazine (Bontril) is a prescription appetite suppressant for short-term use, a few weeks, alongside diet and exercise in people with obesity. It is a Schedule III controlled substance related to amphetamine. It raises heart rate and blood pressure and can be misused.
Key takeaways
- What it is: Phendimetrazine is a sympathomimetic appetite suppressant and a Schedule III controlled substance in the US.
- Main uses: Short-term treatment of obesity.
- Timing: effects start in about 1 hour and last 4 to 6 hours (IR); about 12 hours (ER).
- Most dangerous mix: MAO inhibitors (within 14 days), which can cause hypertensive crisis.
- Naloxone: it does not reverse this drug, but give it whenever opioids could be involved.
- Dependence risk: Moderate.
- Legal route: only with a prescription from a DEA-registered clinician, filled by a licensed pharmacy.
What is phendimetrazine?
Phendimetrazine reduces appetite and is approved for a few weeks of use as part of a weight-loss program in people with a body mass index of 30 or more.
Its effect on weight is modest and fades as tolerance develops. Newer medicines such as GLP-1 drugs are now used far more for long-term weight management.
Quick facts
| Fact | Phendimetrazine |
|---|---|
| Generic name | Phendimetrazine tartrate |
| Brand names | Bontril PDM, Bontril SR (discontinued brands) |
| Drug class | Sympathomimetic amine (anorectic) |
| US legal status | Schedule III, prescription only |
| Approved uses | Short-term (a few weeks) management of exogenous obesity, BMI 30 or more |
| Forms | 35 mg tablets; 105 mg extended-release capsules |
| Onset | About 1 hour |
| Active metabolite | Phenmetrazine |
How long does phendimetrazine last?
- Starts working: About 1 hour
- Effects last: 4 to 6 hours (IR); about 12 hours (ER)
It is approved for a few weeks.
Timing varies with the dose, the form, how it is taken, liver and kidney function, age, and other drugs taken at the same time.
What are the biggest risks of phendimetrazine?
Common side effects include restlessness, insomnia, dry mouth, fast heartbeat, and raised blood pressure.
Heart and lungs: appetite-suppressant stimulants raise heart rate and blood pressure. Rare but serious risks include pulmonary arterial hypertension and heart valve disease, especially when combined with other weight-loss drugs.
Dependence: they are chemically related to amphetamine and can be misused; tolerance to the appetite effect develops within weeks.
What should you never mix with phendimetrazine?
| Combined with | What happens | Label guidance |
|---|---|---|
| MAO inhibitors (within 14 days) | Hypertensive crisis | Contraindicated |
| Other weight-loss drugs and stimulants | Heart and lung risks; overstimulation | Do not combine |
| Alcohol | Dizziness and masked impairment | Avoid |
| Insulin and diabetes medicines | Lower blood sugar as appetite falls | Dose adjustment may be needed |
| Blood pressure medicines | Reduced effect | Monitor |
Check any combination with the DoseUses combination checker or ask a pharmacist.
What are the signs of a phendimetrazine overdose, and what should you do?
Overdose causes restlessness, tremor, rapid breathing, confusion, aggression, hallucinations, high blood pressure, and abnormal heart rhythms, followed by fatigue and depression.
If someone may be overdosing
- Call 911 for chest pain, a seizure, trouble breathing, signs of a stroke (face drooping, weakness on one side, slurred speech), a very high body temperature, or if the person collapses.
- Move them somewhere cool and calm, loosen tight clothing, and cool the skin with water. Do not try to hold them down.
- If they become unresponsive or their breathing slows, give naloxone. Street stimulants are often contaminated with fentanyl.
- For advice when the person is awake and stable, call Poison Help at 1-800-222-1222.
What is phendimetrazine withdrawal like, and how long does it last?
Stopping phendimetrazine after regular use does not cause dangerous physical withdrawal, but it can cause a temporary crash.
- Days 1 to 3CrashTiredness, increased sleep, hunger, and low mood.
- Week 1AdjustingLow energy, poor concentration, and irritability.
- Weeks 2 to 4SettlesMood and energy usually return to baseline.
See the withdrawal timelines and the full phendimetrazine withdrawal guide.
Is phendimetrazine legal?
In the United States, phendimetrazine is a Schedule III controlled substance. The only legal way to get it is with a prescription from a clinician registered with the Drug Enforcement Administration (DEA), filled by a licensed pharmacy. Depending on state law, that can be a physician, nurse practitioner, or physician assistant.
- Refills: a Schedule III prescription can be refilled up to five times within six months of the date it was written. After that, a new prescription is needed.
- Telehealth: federal flexibilities let DEA-registered clinicians prescribe Schedule II to V medicines after a telemedicine visit, without a prior in-person exam, through December 31, 2026. A permanent DEA rule was under final review in late 2026. State rules can be stricter.
- Monitoring: prescribers and pharmacists in most states check a prescription drug monitoring program, a database of controlled-substance prescriptions, before prescribing or dispensing.
Outside the United States
| Country | Status |
|---|---|
| International | Schedule IV of the 1971 Convention on Psychotropic Substances |
Frequently asked questions about phendimetrazine
Is phendimetrazine like phentermine?
Yes. Both are amphetamine-related appetite suppressants for short-term use.
How much weight can you lose on phendimetrazine?
Average extra weight loss in trials was modest, a few pounds over a few weeks.
Is phendimetrazine addictive?
It can be misused and cause dependence; it is a Schedule III controlled substance.
Can phendimetrazine be combined with phentermine?
No. Combining appetite suppressants raises heart and lung risks.
How long can I take phendimetrazine?
It is approved for a few weeks.
Sources
- Bontril (phendimetrazine) prescription information, DailyMed, US National Library of Medicine.
- Controlled Substance Schedules, DEA Diversion Control Division.
- 21 CFR 1306.22, Refilling of prescriptions (Schedules III and IV), Electronic Code of Federal Regulations.
- Prescribing controlled substances via telehealth, US Department of Health and Human Services.
- BeSafeRx: Your Source for Online Pharmacy Information, US Food and Drug Administration.
- Safe Pharmacy, National Association of Boards of Pharmacy.
- One Pill Can Kill, US Drug Enforcement Administration.
- International drug control conventions, United Nations Office on Drugs and Crime.
This guide summarizes the sourced DoseUses Phendimetrazine profile, written from FDA labels, DEA rules, and federal health agencies. It is educational and is not medical advice. Last updated October 5, 2026.
