Learn about Phentermine

The most widely prescribed weight-loss medication in the United States.

Smiling young woman surrounded with pills
About phentermine

Phentermine Overview

Learn about phentermine and succeed in your weight loss journey.

Phentermine is a schedule IV prescription drug used to treat obesity. It can help suppress appetite and make you feel full longer.

First approved in 1959, phentermine is the most-prescribed weight loss medication in the United States. It has been proven effective for short-term weight loss when used alongside a reduced-calorie diet and exercise.

Popular phentermine brands currently prescribed in the United States are Adipex, Qsymia (phentermine-topiramate), and Lomaira.

Well-known brands from Mexico and Chile include Acxion and Terfamex.

Discover all phentermine brands

While phentermine 37.5 mg is the most commonly-prescribed dose of phentermine, daily phentermine dosage varies widely from patient to patient:

8 mg1-3 times per day, 30 minutes before meals
15 mg1-2 times per day, 2 hours after eating
18.75 mg1-2 times per day, on an empty stomach
30 mgOnce per day, before breakfast or 1-2 hours after breakfast
37.5 mgOnce per day, before breakfast or 1-2 hours after breakfast

Learn more about phentermine dosage

Phentermine produces a wide range of unpleasant side effects. The severity of these reactions ranges from mild to life-threatening.

Common side effects of phentermine include headache, insomnia, dry mouth, and constipation.

Tell your doctor right away if you have any serious side effects, such as irregular heartbeat, mood changes (such as phen rage, hallucinations, nervousness), uncontrolled muscle movements, or a change in sexual desire.

Stop taking phentermine and get medical help right away if you have very serious side effects. These include severe headaches, trouble speaking, seizure, weakness on one side of the body, or blurred vision.

It’s important to understand the risks before undergoing treatment with this medication.

See all phentermine side effects

A doctor’s assessments of potential weight loss and possible side effects are crucial. Still, many users also want to hear the opinions and reviews from patients that lost or are trying to lose weight with phentermine.

u003cstrongu003e11 Pounds x 3 Weeksu003c/strongu003e

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About 3 weeks ago, I made a complete lifestyle change. I’m working out 4 days a week. Drinking smoothies and eating smaller portions. I went in for my monthly check-up and lost 11 pounds. I look forward to the next couple of months.

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Lost 22 pounds! I am tapering down my medication now (under supervision). I already track my calories, but what I liked best about the phentermine was that I don’t think about food, and emotional eating is kept better in check.

Read more reviews

Phentermine before and after pictures and hearing about the detailed results from actual users is a vital source of information and motivation as you embark on a weight loss journey of your own.

Brent lost 90 pounds
Sabrina lost 50 pounds

See more results

Phentermine hydrochloride (phentermine HCL) is the active ingredient in phentermine weight loss pills. It is a class IV controlled substance because of its serious side effects and addiction potential.

Phentermine is, therefore, not available over the counter. A doctor’s prescription is needed if you want to lose weight with phentermine.

Most people get their phentermine prescription from a family or primary care doctor. Another option is specialists, such as bariatric doctors or gynecologists. Also, consider a weight loss clinic if you do not have health insurance, do not have a primary care doctor, or cannot find a doctor in your network that prescribes phentermine.

Learn about how to get a prescription

Phentermine comes with many undesirable side effects.

Is There a Safe Alternative to Phentermine?

Yes, there is! It’s called PhenQ.

Many people fear the strong and potentially life-threatening side effects of phentermine and ultimately decide NOT to take the medication.

Instead, 190,000 people chose the natural phentermine alternative, PhenQ, which is proven to produce no side effects at all. Plus, it is readily available without a prescription!

Popular Questions

Naturally, users have many questions about phentermine. Here are some of the most frequently asked ones:

Phentermine is a stimulant that has a chemical structure similar to amphetamines and carries a risk of dependence and abuse.

The United States Drug Enforcement Administration classifies phentermine as a class IV controlled substance. Therefore, phentermine is only available under a doctor’s prescription.

A combination of phentermine and topiramate is used together with a reduced-calorie diet and proper exercise to treat obesity.

Phentermine HCL works as a central nervous system stimulant to suppress hunger and boost energy. Topiramate is an anti-seizure medication that promotes weight loss as well. It increases feelings of fullness, makes food taste less appealing, and increases caloric expenditure.

Phentermine/topiramate is sold under the brand name Qsymia.

The minimum expected weight loss on phentermine is ≥5% of body weight in three months. In a trial, taking 37.5mg of phentermine for three months helped half of the participants lose at least 10% of their baseline body weight. 

The weight you can lose is, however, not a precise figure because weight loss varies so significantly from person to person. While some patients lose 20 or more pounds in a single month, others struggle to drop even one pound per week. 

Here are the 3-month weight loss goals for patients at different starting weights:

Starting Weight (lbs)Short-Term Goal (-5%)Pounds to Lose

Read more about the expected weight loss with phentermine

Adults and children 16 years of age and older usually take phentermine first thing in the morning, before breakfast, or 10 to 14 hours before sleeping.

Phentermine is a stimulant. Hence, if you take phentermine late at night, you could experience problems sleeping.

It is important to always take phentermine as directed by your doctor.

Learn more about how to take phentermine

Phentermine 37.5 should be taken as directed by your doctor, usually once a day on an empty stomach before breakfast or 1 to 2 hours after breakfast.

Always take phentermine as directed by your doctor.

The Food and Drug Administration approves phentermine for use for up to 12 weeks (3 months).

Since weight loss results vary from person to person, some doctors and weight loss clinics might prescribe it for longer use.

There is no difference in weight loss results between phentermine capsules and tablets. Both capsules and tablets contain Phentermine HCL as the active ingredient and therefore have the same effects on your body.

One disadvantage of phentermine tablets is that they need to swell up and disintegrate to release the ingredients. Capsules, on the other hand, have a much better absorption rate than tablets as they begin to dissolve immediately in the stomach.

Another disadvantage of tablets is that they can pass through the body without being completely absorbed.

However, tablets are cheaper to produce, so patients often find that their prescription is cheaper to fill.

Read more about tablets vs capsules

There are several reasons you might not lose weight with phentermine, including:

  • Eating too much or too little
  • Not enough sleep
  • An undiagnosed health issue, such as PCOS or diabetes
  • Not getting sufficient vitamins
  • Stress
  • No exercise
  • Not drinking enough water

If you have been taking phentermine for a long time or are taking it for the second or third time, the body adapts to phentermine, and its effectiveness can decrease.

Read more

Because of the body’s natural response to weight reduction and increased phentermine tolerance, users report that their phentermine has stopped working.

Some of the best tips to avoid such a situation include regular exercise, eating nourishing foods, staying hydrated, prioritizing sleep, setting SMART goals, and adding a supplement.

Read more about phentermine stopped working

Phentermine can appear on a drug test as a false positive for amphetamine.

Although phentermine is not an amphetamine, its chemical structure is similar to that of amphetamine, meaning that phentermine can give a false-positive result for amphetamine in a 5-panel drug screening urinalysis.

Read more phentermine and drug tests

Although this varies depending on the person and their urinary pH, phentermine (Adipex) has a half-life of about 16-31 hours under normal conditions.

Phentermine should not be detectable in the urine after a period of around four or seven days.

Read more

37.5 mg is the highest dose of phentermine available in most countries, including the US, Mexico, Argentina, and Chile.

Phentermine 37.5mg is also the most commonly-prescribed dose due to its widespread availability, high effectiveness, relative affordability, and overall convenience.

Learn more about phentermine 37.5mg

What if I Cannot Get a Prescription for Phentermine?

Try PhenQ. The Official OTC Alternative.

Many people hear about phentermine and maybe even talk to their doctor about it, but ultimately decide NOT to take the medication. Instead, they choose the #1 phentermine alternative, PhenQ, available without a prescription.

Helpful Weight Loss Resources.

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Weight Loss Results With Phentermine

Read the astonishing success stories and look at hundreds of phentermine before and after pictures.

  • Click on the images to learn more about their incredible weight loss journeys and phentermine results!
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