Active ingredient
Phentermine: FDA Status, Uses, Safety and Cost
Stimulant-type appetite suppressant
What Phentermine is
Phentermine is the oldest FDA-approved weight-loss medication still in wide use, approved in 1959. It is a stimulant-type appetite suppressant, available as low-cost generics, and is FDA approved only for short-term use — unlike modern chronic weight-management drugs. It is a federally controlled substance (Schedule IV).
Key facts
| Generic (active ingredient) | Phentermine |
|---|---|
| Brand names | Adipex-P, Lomaira |
| Drug class | Sympathomimetic amine (appetite suppressant) |
| Manufacturer | Multiple manufacturers (generic) |
| FDA status | FDA ApprovedApproved for chronic weight management |
| Administration | Oral tablet or capsule |
| Frequency | Typically once daily (see labeling; Lomaira is dosed differently) |
| Approval date | 1959 |
| Prescription required | Yes |
| Controlled substance | Schedule IV |
| Official label | Prescribing information (DailyMed) |
What Phentermine is approved for
- Short-term (a few weeks) adjunct in a regimen of weight reduction for exogenous obesity, alongside exercise, behavioral modification, and caloric restriction
How Phentermine works
Phentermine is a sympathomimetic amine, pharmacologically related to amphetamine. It suppresses appetite through stimulant effects on the central nervous system.
Administration
Phentermine is given by oral tablet or capsule, typically once daily (see labeling; lomaira is dosed differently).
We do not publish dosing guidance
Dose selection, titration schedules, and what to do about a missed dose are individual clinical decisions. Follow the instructions from your prescriber and the official prescribing information — never a website.
Important safety information
The FDA labeling for Phentermine does not include a boxed warning. It does include warnings and precautions — read the full prescribing information, linked in Sources below.
Contraindications (who should not take it)
- History of cardiovascular disease (e.g., coronary artery disease, stroke, arrhythmias, uncontrolled hypertension)
- Use during or within 14 days of MAO inhibitors
- Hyperthyroidism
- Glaucoma
- Agitated states or history of drug abuse
- Pregnancy and nursing
Summarized from the FDA prescribing information. This is not the complete list — see the full label.
Common adverse reactions from official labeling
- Increased heart rate / palpitations
- Elevated blood pressure
- Insomnia
- Restlessness
- Dry mouth
- Constipation
The most common adverse reactions listed in the product’s FDA prescribing information. Frequency and full adverse-reaction data are in the label.
Cost and access
- Available as inexpensive generics at most pharmacies with a prescription.
- As a Schedule IV controlled substance, prescribing and refills are more restricted than for non-controlled medications.
Why we don't publish a price
List prices, savings-card amounts, and self-pay offers change frequently and vary by pharmacy, plan, and location. Any figure we printed would be wrong for many readers and stale within weeks. See our cost guide for how to get an accurate number for your own situation.
Insurance considerations
- Even when weight-loss drugs are excluded, generic phentermine is often inexpensive enough that patients pay cash; coverage varies by plan.
More detail: how insurance coverage works for weight-loss medication.
Frequently asked questions
- Is phentermine approved for long-term use?
- No. Phentermine alone is FDA approved only as a short-term (a few weeks) adjunct for weight reduction. The combination product Qsymia (phentermine-topiramate) is approved for chronic weight management.
- Is phentermine a controlled substance?
- Yes — phentermine is Schedule IV under the federal Controlled Substances Act.
Sources
- Phentermine prescribing information (DailyMed, NIH) — DailyMed/NIH. Link last verified August 12, 2026.
- Drugs@FDA database — FDA. Link last verified August 12, 2026.
Not medical advice. WeightLossDrugsGuide is an independent educational publisher. We are not a pharmacy, a medical provider, or a telehealth clinic, and we do not provide personalized medical recommendations or dosing guidance. Information here summarizes official FDA labeling and other primary sources and may not reflect the most recent changes. Always talk with a licensed clinician about your own situation, and read the full prescribing information for any medication.