Phentermine: uses, dosing, side effects & brands
Phentermine is a medicine sold in the U.S. under 4 brand and generic names. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.
Key facts
- Available as
- Capsule · Tablet · Tablet, orally disintegrating
- Sold as
- 4 products — Fastin, Ona-Mast and Phentermine Hydrochloride, and others
- Prescription?
- Prescription only
- Generic available?
- Yes
- What the pharmacy pays
- about $3 for a 30-count supply — not your price
Every phentermine product we track (4)
Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.
| # | Drug | Rating | Type | Form | Generic? | Pharmacy pays | |
|---|---|---|---|---|---|---|---|
| 1 | 72/100 | Prescription | Capsule | Generic | $3 | View → | |
| 2 | Not yet rated | Prescription | Capsule | Generic | $3 | View → | |
| 3 | Not yet rated | Prescription | Capsule | Generic | $3 | View → | |
| 4 | Not yet rated | Prescription | Tablet | Generic | $3 | View → |
Phentermine is one of the FDA-approved weight-loss medications — see every option compared (injections and pills, with each trial’s average weight loss).
What phentermine pills look like
Imprint codes, colour and shape from the FDA’s labelling data. Match the imprint on your pill — or search any imprint.
Combination products containing phentermine
A combination is a different drug — different dosing, different warnings. It is listed here so you can find it, not so you can substitute it.
Phentermine recalls
From the FDA Enforcement database. A recall covers specific lots — not the drug as a whole.
How long phentermine keeps
No phentermine label we read sets a separate limit for after opening, but they do specify how it must be stored — and the stability behind any date assumes those conditions.
What people report to the FDA about phentermine
The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 1,102 reports naming phentermine, and the FDA flagged 42% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:
- fatigue79 reports
- headache69 reports
- nausea55 reports
- arthralgia50 reports
- anxiety46 reports
- pruritus39 reports
- dyspnoea38 reports
- weight increased36 reports
Read these as a signal, not a rate. A report does not mean phentermine caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label.
Source: openFDA drug/event (FAERS), retrieved August 27, 2026.
Related guides
Related calculators
Frequently asked questions
Can you take phentermine with other medicines?
It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run phentermine against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.
What brand names is phentermine sold under?
We track 4 phentermine-containing products in the U.S.: Fastin, Ona-Mast, Phentermine Hydrochloride and Suprenza. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.
What forms does phentermine come in?
Across the brands we track, phentermine is currently marketed as capsule, tablet and tablet, orally disintegrating, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.
Is there a generic phentermine?
Yes. Our catalog lists 2 generic phentermine products alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.
Has phentermine been recalled?
The FDA's Enforcement database lists 1 recall record whose product description mentions phentermine. The most recent: Phentermine Hydrochloride Capsules (May 9, 2025). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.
Cite this page
- APA
- pharmaranks. (2026, July 24). Phentermine: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/phentermine
- MLA
- “Phentermine: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/phentermine.
We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.
Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.
Read the full FDA label for phentermine on DailyMed (NIH) ↗.