Phentermine vs semaglutide (Wegovy) for weight loss: compared
Phentermine is an inexpensive stimulant appetite suppressant approved for short-term use; semaglutide (Wegovy) is a weekly injection, or daily tablet, approved for long-term weight management. In trials, semaglutide produced substantially more weight loss on average, but it costs far more and is often not covered.
Updated October 4, 2026
At a glance
- How it works
- Phentermine
- Stimulant that suppresses appetite
- Semaglutide
- GLP-1 medicine that reduces appetite and slows digestion
- Approved length of use
- Phentermine
- A few weeks
- Semaglutide
- Long term
- Form
- Phentermine
- Daily tablet or capsule
- Semaglutide
- Weekly injection or daily tablet
- Controlled substance
- Phentermine
- Yes, Schedule IV
- Semaglutide
- No
- Cost
- Phentermine
- Inexpensive generic
- Semaglutide
- Brand-only and costly; coverage varies
Phentermine Adipex-P, Lomaira | Semaglutide Wegovy | |
|---|---|---|
| How it works | Stimulant that suppresses appetite | GLP-1 medicine that reduces appetite and slows digestion |
| Approved length of use | A few weeks | Long term |
| Form | Daily tablet or capsule | Weekly injection or daily tablet |
| Controlled substance | Yes, Schedule IV | No |
| Cost | Inexpensive generic | Brand-only and costly; coverage varies |
Effectiveness and duration
Semaglutide is approved for long-term use and, in its trials, produced substantially more weight loss on average than older medicines; it is also approved to lower heart attack and stroke risk in people with heart disease. Phentermine is approved for a few weeks as part of a diet and exercise program, though prescribers sometimes use it longer, and phentermine combined with topiramate (Qsymia) is approved for long-term use.
Side effects
Phentermine raises heart rate and blood pressure and can cause trouble sleeping, dry mouth and anxiety, so it is not used with heart disease, uncontrolled blood pressure, an overactive thyroid or glaucoma, or with MAOIs. Semaglutide commonly causes nausea, constipation and diarrhea, mostly early and after dose increases, and carries warnings about pancreatitis, gallbladder disease and a thyroid tumor class warning.
After stopping
Weight usually returns after either medicine is stopped unless habits change, which is why semaglutide is intended as a long-term treatment and why both are paired with eating and activity changes.
Cost and coverage
Phentermine is an inexpensive generic that pharmacies price very differently, so comparing quotes helps. Wegovy is brand-only; coverage for weight management depends on your plan, and the manufacturer sells it directly to self-paying patients. See our guide to GLP-1 coverage by insurance type.
Who decides
The right choice depends on your health, other medicines, goals and budget, and it is a decision to make with your prescriber; the two are not usually combined.
Questions for your prescriber
- Is a short-term or long-term medicine right for my goals?
- Do my heart health or blood pressure rule out phentermine?
- What will my plan cover, and what would self-pay cost?
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Sources
Written by the Script Unlock editorial team from the sources above. It is general information, not advice for you or your pet; your prescriber decides which medicine is right.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.