How Long Can You Take Phentermine?

Phentermine's FDA label calls it a short-term treatment, used for 'a few weeks' alongside a reduced-calorie diet, exercise and behavior change. MedlinePlus notes that most people take it for 3 to 6 weeks, and that the length depends on how you respond. How long it makes sense for you is your provider's decision, reviewed with you every month.

At Padgett Medical Center in Tampa, your first month of phentermine is $127.40 when you book online with a card on file, 35% off the regular $196. It includes the visit, the first month of phentermine and a B12 injection. Nothing is charged when you book. See the phentermine program.

What does 'short-term' mean on the phentermine label?

The label says phentermine is indicated as a short-term adjunct, 'a few weeks', to a weight-loss plan built on exercise, behavior change and fewer calories. It doesn't name an exact number of weeks.

The prescribing information also says the limited usefulness of this class of medication should be weighed against its possible risks, and that the clinical trials behind it lasted only a few weeks. 'Adjunct' matters too: phentermine is meant to support the eating and activity changes, not replace them.

How long do most people take phentermine?

MedlinePlus says most people take phentermine for 3 to 6 weeks, and that the length of treatment depends on how you respond to the medication.

MedlinePlus also notes that phentermine can be habit-forming, so you shouldn't take a larger dose, take it more often or take it for longer than your provider tells you to. Your prescription and your provider's instructions, not a general rule, set your timeline. At Padgett, the first month is a chance to see how you respond: at your next visit, your provider looks at how your appetite, weight and blood pressure changed before deciding on another month.

Do some providers prescribe phentermine for longer?

Yes. NIDDK notes that some health care professionals prescribe appetite suppressants like phentermine for longer than the few weeks the FDA approved, and that not many studies have looked at how safe and effective they are for long-term use.

Using a medication in a way that differs from its FDA approval, including for a longer time, is called off-label use. That describes what happens in practice in some places. It isn't what the label says, and it isn't a standard that applies to everyone.

What does research say about longer use?

Research on longer use is limited. One observational study of about 14,000 adults, published in Obesity in 2019, found that people who stayed on phentermine longer lost more weight on average, and that heart problems or death were rare, with no significant difference between groups.

The study used electronic health records, and its authors noted the limits of an observational design and described their findings as applying to lower-risk individuals. A single study like this doesn't change the label, and it doesn't predict how phentermine will work for you.

What happens if phentermine stops working?

The appetite-lowering effect can fade, which is called tolerance. The label says tolerance usually develops within a few weeks, and that when it does, you shouldn't take more than the recommended dose to get the effect back; instead, phentermine should be stopped.

If you notice your appetite coming back, don't take an extra pill or double your dose. Tell your provider at your monthly visit, or call sooner. That's the conversation where you and your provider decide what makes sense next.

What happens when you stop taking phentermine?

Some weight often comes back after weight-loss medication stops. NIDDK says healthy eating habits and more physical activity may help you regain less or keep it off.

That's why the habits you build while taking phentermine matter as much as the pill. Plan for the end from the start: regular meals, enough protein, daily movement and good sleep. For ideas, read how to keep the weight off.

How does Padgett decide how long you take it?

Your provider decides how long it makes sense for you, sees you every month while you take it, and talks through what comes next.

Signs it may be time to talk about stopping include your appetite coming back, side effects that don't settle, a rise in your blood pressure, or reaching the goal you set together. Bring any of these up at your visit, or call sooner if something worries you.

Each monthly visit with Morgan Colee, PA, includes a blood pressure check and a review of your appetite, side effects and progress, and each refill is $166, including the visit, the medication and a B12 injection. What comes next depends on you: it may mean continuing the habits on your own, or talking about a different approach, such as a weekly GLP-1 medication. Read how we personalize your plan for how those decisions are made. Book your phentermine visit.

This article is educational and is not medical advice. Talk with a licensed provider about your own health, medications and treatment options.