Phentermine: uses, side effects and safety
Phentermine (Adipex-P) is a sympathomimetic amine anorectic. It is a US Schedule IV controlled substance. It is prescription only; product discontinued and is no longer marketed in the US. The brand is discontinued as a labeled product but the active ingredient remains a legitimately approved, currently marketed generic.
What is Phentermine?
Phentermine is the generic name for Adipex-P, and belongs to the Sympathomimetic amine anorectic class.
| Generic name | phentermine |
|---|---|
| Brand name(s) | Adipex-P |
| Drug class | Sympathomimetic amine anorectic |
| US legal status | US Schedule IV · Prescription only; product discontinued · Product discontinued |
| Route | Oral |
| Prescription required | Yes |
| Time to peak concentration | 3-4.4 hours |
What is Phentermine used for?
Phentermine is approved by the FDA for the following uses. Approval is granted per indication, and a specific product may not be approved for all of them.
- Short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction, in the management of exogenous obesity
How does Phentermine work?
Sympathomimetic amine with pharmacologic activity similar to amphetamine (d- and d,l-amphetamine)..
Common side effects of Phentermine
These are the side effects people report most often. Many diminish after the body adjusts, usually within one to two weeks.
- Dry mouth / unpleasant taste
- Diarrhea
- Constipation
- Insomnia
- Overstimulation
- Restlessness
- Dizziness
- Headache
- Tremor
What does Phentermine interact with?
Interactions matter because two safe medicines can become dangerous together. The entries below are the ones most likely to cause harm.
- MAOIs: contraindicated during or within 14 days of MAOI use - risk of hypertensive crisis
- Alcohol: concomitant use may result in an adverse drug reaction
- Insulin and oral hypoglycemic medications: requirements may be altered
- Adrenergic neuron blocking drugs: phentermine may decrease their hypotensive effect
Use our drug interaction checker before combining any two prescriptions.
Serious side effects and warning signs
Seek emergency care for any of these
- Primary pulmonary hypertension (rare, frequently fatal)
- Serious regurgitant cardiac valvular disease
- Psychosis
- Hypertensive crisis with MAOIs
Suspected overdose or a bad reaction should be reported to Poison Control on 1-800-222-1222. That is staffed around the clock and is free.
Legal status of Phentermine
Phentermine is a Schedule IV controlled substance in the United States. That placement is set out in Title 21 of the Code of Federal Regulations, Part 1308, and enforced by the Drug Enforcement Administration. It carries restrictions on prescribing, storage, record-keeping and transfer.
Statutory reference: 21 CFR 1308.14(f)(9) - Phentermine (DEA code 1640).
Important note
The brand is discontinued as a labeled product but the active ingredient remains a legitimately approved, currently marketed generic. Adipex and Adipex-P both returned zero SPLs from the DailyMed drug_name search, so dailymedSetid is null. All pharmacologic and adverse-reaction data above were taken from the current generic phentermine hydrochloride label (setid 129e781c-5366-4986-8e67-6b35fa4c3f39), which markets only the 37.5 mg strength; the historical Adipex-P 15 mg and 30 mg strengths could not be verified from a current primary source and are therefore not listed. fdaApprovalDate is null: FDA Drugs@FDA returned no original NDA for Adipex-P (NDA019199 is not present in the endpoint; only ANDAs appear, whose dates are unreliable), and no date was guessed. metabolism and halfLife are null because the current label reports neither. peakHours is stored as the string '3-4.4 hours' because the label gives a range. Note phentermine/topiramate combination capsules (Qsymia) are a separate product and a separate indication.
Can you get Phentermine without a prescription?
Short answer: no. Phentermine is a prescription medication. Sites advertising it without one are either operating illegally or selling something other than what they claim. We explain the legal routes, the counterfeit problem and how to check a source in detail.
Read the full answer: Phentermine without a prescription →
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Read more →Frequently asked questions
What is Phentermine used for?
Short-term (a few weeks) adjunct in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction, in the management of exogenous obesity
What schedule is Phentermine in the United States?
Phentermine is a Schedule IV controlled substance in the US, listed at 21 CFR Part 1308. Schedule IV means the drug has a defined potential for abuse and is subject to federal record-keeping, storage and prescribing restrictions.
What are the common side effects of Phentermine?
The most frequently reported side effects are dry mouth / unpleasant taste, diarrhea, constipation, insomnia, overstimulation, restlessness. Many lessen over the first week or two of treatment.
What should not be combined with Phentermine?
The most clinically important interactions are with maois: contraindicated during or within 14 days of maoi use - risk of hypertensive crisis, alcohol: concomitant use may result in an adverse drug reaction, insulin and oral hypoglycemic medications: requirements may be altered, adrenergic neuron blocking drugs: phentermine may decrease their hypotensive effect. Always give a pharmacist or prescriber a complete list of everything you take, including over-the-counter drugs and supplements.
Sources & references
Important
This site provides educational information only and does not sell, prescribe or dispense medications. Always consult a licensed healthcare provider. This page is not medical advice.