Phentermine for weight loss

Dr. Daniel Hodge

One of the oldest obesity treatment medications still in use is phentermine. It was FDA approved in 1959 as an appetite-suppressing medication and is currently approved as a short-term weight loss treatment. Let’s learn a bit more about what phentermine is and how it can help with obesity treatment and weight loss.

  • What is Phentermine?
  • How does Phentermine help you lose weight?
  • What are the average weight loss results on Phentermine?
  • Who can take Phentermine?
  • What are the most common side effects of Phentermine?
  • How much does Phentermine cost?
  • How do I access the Phentermine savings card?
  • How do I get a prescription for Phentermine with Sequence?

What is Phentermine?

Phentermine is a prescription medication that is used as an appetite suppressant to help patients lose weight. It is typically prescribed for individuals who are obese or have a weight-related medical condition, such as type 2 diabetes, high blood pressure, or elevated cholesterol levels. It is important to note that phentermine should only be used under the supervision of a healthcare provider, and should not be used as a long-term weight loss solution.

How does Phentermine help you lose weight?

Phentermine is a stimulant that decreases appetite and increases feelings of fullness, which can help people reduce the amount of food they eat and lose weight. It works by increasing levels of norepinephrine, a neurotransmitter that is involved in the "fight or flight" response. When the sympathetic nervous system is activated, it can increase the release of certain neurotransmitters, such as norepinephrine and dopamine, which can help suppress appetite by activating certain areas of the brain called the hypothalamus, which plays a role in a variety of hormone signaling pathways in the body. It is usually taken as a pill once daily for 12 weeks (3 months)  and is typically used in combination with diet and exercise to promote weight loss.

What are the average weight loss results on Phentermine?

There have been several clinical trials that have evaluated the effectiveness of phentermine for weight loss. In general, these studies have found that phentermine can help people lose weight when it is used in combination with lifestyle intervention.

One 12-week randomized, double-blind, placebo-controlled trial enrolled patients based on BMI criteria for obesity (>30 kg/m2) or overweight (BMI 27+kg/m2 with a risk factor for obesity) and found that 95% of those who took phentermine lost at least 5% of their total body weight while 62% lost at least 10% body weight.

Another 28-week, randomized, controlled trial found that individuals taking Phentermine 15 mg daily had an average of 7.38% body weight loss, compared to 2.28% weight loss in those taking the placebo. That study also investigated phentermine as part of combination therapy: phentermine-topiramate (brand name Qysmia). The combinations of phentermine 15 mg and topiramate 92 mg performed the best, with an average body weight loss of 11.63%.



Similarly, in a 2016 JAMA review of different weight loss medication studies, the combination of phentermine-topiramate performed the best, with 75% of participants achieving at least 5%  body weight loss and 54% achieving at least 10% body weight loss after 1 year— though all active agents in that study were associated with significant weight loss compared with the placebo at 1 year. 

Overall, phentermine is an effective weight loss tool approved by the FDA for short term use and is most effective when used in combination with diet and exercise—and, in some cases, topiramate. There is growing clinical interest in using phentermine monotherapy for long term weight loss treatment and a recent trial suggests that this may help to prevent weight regain after discontinuation. However, this treatment is not approved by the FDA as a chronic weight loss treatment option at this time, further research is needed to determine the safety and effectiveness of phentermine for long-term use. To that end, a trial began in June 2022.

Who can take Phentermine?

Phentermine is a prescription medication that is typically only recommended for people who are obese or have a weight-related medical condition, such as type 2 diabetes or high blood pressure. It is usually prescribed to people who have a body mass index (BMI) of 30 or higher, or a BMI of 27 or higher with a weight-related medical condition.

Phentermine is generally not recommended for people who have certain medical conditions or are taking certain medications, as it may not be safe for them. For example, phentermine may not be suitable for people who have:

  • Heart disease
  • High blood pressure
  • Glaucoma
  • Hyperthyroidism
  • History of drug abuse

Phentermine may also interact with certain medications, so it is important to tell your healthcare provider about all the medications you are taking before starting phentermine.

In the U.S., phentermine is a Schedule 4 drug, meaning it is a controlled substance and has the possibility of misuse. It is considered a stimulant with limited dependence liability and thus requires regular followup and monitoring with your provider. Additionally, make your provider aware if you have had an adverse reaction to another stimulant medication previously.

What are the most common side effects of Phentermine?

The most common side effects of phentermine include:

  • Dry mouth
  • Nervousness or restlessness
  • Insomnia or difficulty sleeping
  • Agitation or irritability
  • Palpitations (irregular heartbeat)
  • High blood pressure
  • Increased heart rate
  • Constipation
  • Diarrhea
  • Nausea or vomiting

Less common side effects of phentermine may include:

  • Chest pain
  • Shortness of breath
  • Fast or pounding heartbeat
  • Changes in libido (sex drive)
  • Swelling of the face, ankles, or hands

If you experience any side effects while taking phentermine, it is important to tell your healthcare provider. In some cases, your healthcare provider may adjust your dosage or recommend a different medication. It is important to follow your healthcare provider's instructions when taking phentermine to minimize the risk of side effects.

How much does Phentermine cost?

Phentermine is a generic medication and, as such, is usually affordable. Most people in the U.S. can find it for $10 - $20, particularly when using a coupon site like GoodRx

How do I get a prescription for Phentermine with Sequence?

Since phentermine is a controlled substance, we do not currently offer it through our telehealth platform as most state laws require an in-person evaluation for controlled substances. With that said, there are a variety of other medications that might be a good fit, which our clinicians can evaluate you for. To see if you’re a good fit for our comprehensive weight loss program, take our 5-minute quiz.

Otherwise, you can also speak to your primary care physician, obesity medicine provider, or endocrinologist about phentermine to see if it’s right for you. 

Dr. Daniel Hodge

About the Author

Dr. Daniel Hodge is board-certified in both internal medicine and obesity medicine with an expertise in chronic disease management, medical weight loss, and urgent care. Dr. Hodge aims to provide a personalized approach to health and wellness that works for our Sequence members.

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