Adipex-P (Phentermine) at a glance: schedule, half-life, and class
- Generic name
- Phentermine hydrochloride
- Brand names
- Adipex-P, Lomaira; with topiramate: Qsymia
- Drug class
- Sympathomimetic amine (anorectic)
- US legal status
- Schedule IV, prescription only
- Approved uses
- Short-term treatment of obesity (BMI 30 or more, or 27 or more with a risk factor)
- Forms
- Tablets, capsules
- Onset
- About 1 hour
- Half-life
- About 20 hours
- Duration of use
- A few weeks (phentermine alone)
- Key warning
- Heart and lung complications; avoid with heart disease
Adipex-P uses: what phentermine is prescribed for
Phentermine is approved as a short-term (a few weeks) add-on to diet, exercise, and behavior change for adults with a BMI of 30 or more, or 27 or more with conditions such as high blood pressure or diabetes.[1]
Phentermine/topiramate (Qsymia) is approved for long-term weight management. Newer GLP-1 medicines such as semaglutide and tirzepatide produce more weight loss but cost much more.
Adipex-P dosage: how phentermine is usually prescribed
The figures below come from the FDA-approved label and describe how prescribers typically use phentermine. They are not personal dosing advice. A prescriber sets the dose for each person and adjusts it over time.[1]
| Product | Typical dose | Label guidance |
|---|---|---|
| Adipex-P 37.5 mg | One tablet before breakfast or 1 to 2 hours after | Avoid late doses (insomnia) |
| Lomaira 8 mg | 8 mg up to three times a day, 30 minutes before meals | |
| Qsymia (with topiramate) | 3.75/23 mg for 14 days, then 7.5/46 mg | Long-term use; pregnancy prevention program |
Adipex-P (phentermine) side effects and risks
Common side effects include dry mouth, insomnia, restlessness, constipation, fast heartbeat, and raised blood pressure.[1]
Serious risks include primary pulmonary hypertension and heart valve disease (reported mainly with the older fen-phen combination), and worsening of heart disease. It should not be used with uncontrolled high blood pressure, heart disease, hyperthyroidism, glaucoma, or during pregnancy.[1]
Adipex-P interactions: what not to mix with phentermine
Choose what it would be combined with:
| Combined with | What happens | Label guidance |
|---|---|---|
| MAOIs | High blood pressure crisis | Contraindicated within 14 days |
| Other weight-loss drugs and stimulants | Heart and blood pressure risks | Avoid |
| Alcohol | Adverse reactions | Avoid |
| Insulin and diabetes medicines | Lower glucose as weight drops | Dose may need lowering |
This is not a full list. A pharmacist can check a complete medication list, including supplements and over-the-counter products.[1]
Adipex-P overdose: signs of phentermine overdose and what to do
Overdose causes restlessness, tremor, rapid breathing, confusion, aggression, hallucinations, panic, high or low blood pressure, irregular heartbeat, and seizures.[1]
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 happens when you stop phentermine?
Stopping phentermine after regular prescribed use does not cause dangerous physical withdrawal. ADHD symptoms return, and some people feel tired or low for a few days. After heavy misuse, a "crash" with exhaustion, increased sleep and appetite, and depression is common.[1]
- Days 1 to 3CrashFatigue, long sleep, increased appetite, low mood, irritability.
- Weeks 1 to 2Low mood and cravingsLow energy, poor concentration, and cravings after heavy use.
- Weeks to monthsRecoveryMood and energy normalize; depression should be watched for.
There is no need to taper prescribed stimulants for safety, but anyone who feels severe depression or suicidal thoughts after stopping should contact a clinician or call or text 988.
How to get prescribed Adipex-P (phentermine) legally in the US
In the United States, phentermine is a Schedule IV 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.[2]
- Refills: a Schedule IV prescription can be refilled up to five times within six months of the date it was written. After that, a new prescription is needed.[3]
- 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.[4]
- Monitoring: prescribers and pharmacists in most states check a prescription drug monitoring program, a database of controlled-substance prescriptions, before prescribing or dispensing.
- Pharmacies: a legitimate pharmacy always requires a valid prescription, has a licensed pharmacist available, and is licensed in the state it ships to. The FDA's BeSafeRx tool and the NABP's safe pharmacy list help confirm a pharmacy is real.[5][6]
- Cost: generic phentermine is inexpensive; many insurers do not cover weight-loss medicines.
Traveling: keep the medicine in its original pharmacy container and carry a copy of the prescription. Check the rules of the destination country before travel, because many countries restrict controlled medicines or require a permit.
Can you order Adipex-P (phentermine) online legally?
Yes, but only with a valid prescription and only from a pharmacy licensed in your state. Many licensed pharmacies, including mail-order pharmacies run by insurers, fill phentermine prescriptions online and ship them. Buying phentermine from a website that does not require a prescription is illegal, and the product is often fake.[5][7]
- See a licensed clinicianA clinician evaluates you in person or by telemedicine and decides whether phentermine is appropriate.
- The prescription goes to a pharmacyPrescriptions for controlled medicines are usually sent electronically, straight from the prescriber to the pharmacy you choose.
- The pharmacy checks and fills itA pharmacist verifies the prescription and your identity, then dispenses the medicine in person or by mail.
Signs that an online seller is illegal:
- It sells phentermine with no prescription, or after only a short online questionnaire.
- It takes orders through social media, messaging apps, or email.
- It asks for payment in cryptocurrency, gift cards, or money transfers.
- It has no US street address, no state pharmacy license, and no pharmacist to speak to.
- Its prices are far below those of ordinary pharmacies, or it ships from another country.
The FDA's BeSafeRx tool links to each state's license lookup, and the National Association of Boards of Pharmacy lists verified online pharmacies.[5][6]
Adipex-P price: how much does Adipex-P (phentermine) cost without insurance?
Generic phentermine is inexpensive; many insurers do not cover weight-loss medicines.
What you pay depends on the strength, the number of doses, your insurance plan, and the pharmacy. Cash prices for the same prescription can differ several times over between pharmacies in the same town, so check current prices before you fill it.
Ways to pay less, legally:
- Ask the prescriber whether a generic phentermine is available. FDA-approved generics work the same way as the brand and usually cost much less.
- Compare cash prices between pharmacies before you fill the prescription.
- Use a free prescription discount card, such as GoodRx or SingleCare, when you pay cash. These cards cannot be combined with insurance on the same fill.
- For brand-name medicines, check the manufacturer's savings program or patient assistance program.
- Ask about a 90-day supply or your insurer's mail-order pharmacy, which often lowers the cost per dose when your prescriber agrees it is appropriate.
Warning: A price far below what licensed pharmacies charge, especially with no prescription required, is a strong sign of an illegal seller and counterfeit medicine.[5]
Is Adipex-P legal? Phentermine legal status in other countries
| Country | Status |
|---|---|
| United Kingdom | Class C; not licensed for weight loss |
| European Union | Marketing authorizations withdrawn in 2000 |
| Australia | Schedule 4 prescription medicine |
| International | Schedule IV of the 1971 Convention on Psychotropic Substances |
Laws change and differ in detail. Check current rules before carrying any controlled medicine across a border.[8]
Common questions about Adipex-P (phentermine)
How long can you take Adipex-P (phentermine)?
Alone, it is approved for a few weeks. Some clinicians prescribe it longer off-label. Qsymia, which includes phentermine, is approved for long-term use.
Is Adipex-P (phentermine) like Adderall?
It is chemically related to amphetamine but has much weaker effects on dopamine and a lower risk of misuse.
How much weight do people lose on Adipex-P (phentermine)?
On average about 3 to 5% of body weight beyond diet alone over 12 weeks; results vary.
Was Adipex-P (phentermine) part of fen-phen?
Yes. Fen-phen combined fenfluramine with phentermine. Fenfluramine was withdrawn in 1997 because of heart valve damage; phentermine stayed on the market.
Can you buy Adipex-P (phentermine) without a prescription?
No. Adipex-P (phentermine) is a Schedule IV controlled substance in the US, so it is illegal to buy or possess it without a valid prescription. Websites and social media sellers that offer it without one are not legal pharmacies, and the DEA warns that pills sold this way are often counterfeit and can contain fentanyl. The legal route is a visit with a licensed clinician, in person or by telehealth, and a prescription filled at a state-licensed pharmacy. The FDA's BeSafeRx tool and the NABP's safe pharmacy list help confirm an online pharmacy is real.
Sources
- Adipex-P (phentermine) prescribing 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.
