Semaglutide and phentermine are both drugs that can help with weight loss. It’s unclear whether they should be used together. Phentermine is designed for short-term use, while semaglutide is meant for long-term weight management.

once-weekly semaglutideShare on Pinterest
Photographs by Douglas Cliff/Getty Images; Yuriy_K/Getty Images

People who live with obesity face increased health risks such as greater chances of developing hypertension, heart disease, and type 2 diabetes. That’s why medications, in combination with lifestyle changes, have become so popular for treating obesity and helping with weight loss.

Semaglutide and phentermine are both popular weight loss drugs, but they are very different.

The two medications have similar goals but work in different ways. This article will explain how they can be used to promote weight loss.

Semaglutide and phentermine can generally be used together since they do not interact.

But it’s important to check with your doctor about your specific health needs and whether these drugs are appropriate for your care plan.

Both semaglutide and phentermine can be used in combination with diet, exercise, and behavioral changes to help with weight loss.

However, only the semaglutide medication Wegovy is approved by the Food and Drug Administration (FDA) for weight loss. Two other brand-name semaglutide drugs, Ozempic and Rybelsus, are not approved for weight loss but are often prescribed off-label for that use.

The two medications have some key differences.


  • Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist. It’s commonly sold under the brand names Wegovy and Ozempic in injectable form and Rybelsus in pill form.
  • Although the FDA approved semaglutide for weight loss in 2021, this medication’s use in treating type 2 diabetes and heart disease dates back to Ozempic’s 2017 approval for reducing the risk of heart attack, stroke, or death in people with type 2 diabetes.
  • It works by mimicking the GLP-1 hormone, causing your body to produce more insulin, lowering your blood sugar levels, and signaling fullness to your brain.
  • It’s designed for long-term use, but people who take semaglutide may experience weight gain if they stop taking the medication.
  • It can affect your body’s response to insulin and insulin-releasing medications, so your doctor may need to adjust your dosages of these medications to reduce the risk of hypoglycemia (low blood sugar).
  • Injectable versions of semaglutide may also affect the absorption of other medications taken orally, including over-the-counter aspirin and allergy medications.


  • Phentermine is a sympathomimetic amine that stimulates your central nervous system. The FDA first approved it as an appetite suppressant in 1959.
  • It’s sold under the brand names Adipex-P, Lomaira, and Suprenza.
  • It’s also sold in combination with a drug called topiramate in a medication called Qsymia.
  • It’s unclear exactly how phentermine reduces appetite, but it may increase neurotransmitter levels in your brain.
  • This medication’s effectiveness may diminish over time, and it’s approved for use for only 12 weeks.
  • It is considered a controlled substance that can be addictive and carries the risk of withdrawal symptoms and potential side effects such as a racing or irregular heartbeat.
  • This medication is not recommended for use in people with glaucoma, hyperthyroidism, or a history of cardiovascular disease.

You may experience unpleasant side effects from one of the two drugs or have a strong preference for one type of medication over the other. It’s important to talk with a healthcare professional about any side effects you may experience.

Possible side effects of semaglutide include:

  • nausea and vomiting
  • constipation or diarrhea
  • headache
  • abdominal pain
  • fatigue
  • hypoglycemia

Possible side effects of phentermine include:

Additionally, people who take high doses of phentermine may experience withdrawal symptoms. This medication may also impair your ability to perform potentially hazardous tasks such as using heavy machinery or driving a car.

Semaglutide and phentermine have both been shown to be effective at helping people to lose weight.

While there is not a lot of research comparing the two side by side, some research notes that injectable semaglutide may lead to more weight loss than phentermine.

In a 2021 study, the researchers noted that those who injected semaglutide showed more of a reduction in body weight compared to other people who took other approved weight loss medications, such as phentermine.

But keep in mind that only Wegovy is approved for weight loss, and Ozempic and Rybelsus can be used for that purpose only if a doctor prescribes them off-label. You’ll want to consult your healthcare team about which medication may be most appropriate for your specific health situation.

Semaglutide and phentermine are both drugs that can be used for weight loss. However, there are major differences between these medications, including how they affect your body and how long you should use them.

If you believe that the use of weight loss drugs would benefit your health, it’s important to talk with your doctor. They can work with you to determine the best medication and dosage for your needs.