Wegovy vs. Phentermine for Weight Loss: Which Is Better?

By Terez Malka, MD
Medically reviewed checkmarkMedically reviewed
November 17, 2022

Key takeaways

  • Wegovy and phentermine are both FDA-approved prescription weight-loss medications.

  • Wegovy is a GLP-1 medication intended for long-term use, while phentermine is an appetite-reducing medication approved for short-term use.

  • The best weight loss medication for you depends on your needs and weight loss goals.

Wegovy and phentermine are prescription medications used for weight loss. Wegovy was approved in 2021, becoming one of the newest weight loss drugs on the market. Phentermine was first FDA-approved in 1959 and is one of the oldest weight loss medications available today.

There are many differences between the two medications, including side effects, how they work, and intended duration of use. If you’re interested in taking weight loss medication, it’s important to speak with your healthcare provider about your health and weight loss goals to determine which, if either, is the best option.

Read on to learn more about Wegovy and phentermine, including side effects, drug interactions, dosage, and more.

What is Wegovy?

Wegovy is a glucagon-like peptide-1 (GLP-1) containing the active compound semaglutide. Wegovy gained FDA approval in 2021, becoming the first FDA-approved weight loss medication since 2014

Wegovy contains a higher dose of semaglutide than the other available semaglutide GLP-1 medication, Ozempic—a medication primarily indicated for treating type 2 diabetes. Wegovy is an injectable medication taken once weekly and intended to treat overweight and obesity.

Wegovy is only approved for certain individuals—people with a body mass index (BMI) of 30 or greater or with a BMI of 27 or greater who also have a metabolic health condition, like type 2 diabetes or hypertension. It’s taken alongside behavioral modifications like diet and exercise to help promote weight loss. 

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How does Wegovy work?

Wegovy, like all GLP-1s, works by mimicking the effect of the GLP-1 naturally produced by the gastrointestinal tract. This effect helps improve insulin production, slow stomach emptying, reduce appetite, lower the amount of sugar produced in the liver, and decrease muscle insulin sensitivity. Because Wegovy contains high doses of semaglutide, it crosses the blood-brain barrier more effectively, which helps increase total weight loss.

If prescribed Wegovy, your provider will start you on a low dose of the medication and gradually increase your dosage over 16-20 weeks. The highest dose available is 2.4 mg per week.

What is Phentermine?

Phentermine is a short-term prescription medication used to decrease appetite. It’s typically used alongside a low-calorie diet and exercise to promote weight loss. Phentermine is not intended for long-term use—it’s meant to jumpstart weight loss and help people lose a significant amount of weight quickly. Most people take the medication for 3-6 weeks, but it’s approved for up to 12 weeks.

Weight loss usually stops when the medication is discontinued. In some cases, people may gain weight back after stopping the medication.

How does phentermine work?

Phentermine supports weight loss by decreasing appetite. It’s usually taken as a single daily dose in tablet form in the morning or three times daily 30 minutes before meals. 

Wegovy vs. Phentermine: How Do They Compare?

There are some significant differences to consider when comparing Wegovy and phentermine.

Efficacy

Wegovy has been found to help people lose an average of 6-12% of their body weight. Research also suggests that semaglutide, the active ingredient in Wegovy, can help improve metabolic health and lower the rate of cardiovascular death, non-fatal heart attacks, and non-fatal stroke in people with type 2 diabetes at high risk of cardiovascular disease. 

Phentermine has been shown to successfully help people lose weight quickly. One study of almost 800 obese patients found 45.6% of those taking phentermine lost 5% or more of their body weight. The mean weight loss was around 4 kilograms (about 8 pounds). A long-term controlled trial of phentermine took place in 1968 and found that people who took phentermine for one year lost approximately 13% of their initial weight

Side effects

Both Wegovy and phentermine can cause side effects. The most common side effects of Wegovy are gastrointestinal, including:

The most common side effects of phentermine include:

  • Dry mouth
  • Unpleasant taste
  • Diarrhea
  • Constipation 
  • Vomiting

Cost

The cost of each medication varies depending on several factors, including your insurance coverage and the pharmacy you use. The pricing at pharmacies often varies, so it’s important to compare prices at different pharmacies in your area.

Without insurance, Wegovy can cost over $1,500 per month. With coverage, you may pay as little as $25 per month. Phentermine may cost as little as $8.60 per month with insurance. Companies like GoodRx and SingleCare offer coupons that can help lower the cost.

Safety

Both medications are approved by the FDA and have passed FDA safety standards. However, it’s important to talk to your healthcare provider before starting either medication, as they may not be suitable for everyone.

Wegovy should not be taken by people with a personal or family history of medullary thyroid cancer (a rare and primarily genetic type of thyroid cancer) or people with a rare condition called multiple endocrine neoplasia syndrome type 2 (MEN 2). 

Phentermine can be habit-forming and should be taken under a healthcare provider’s supervision. It’s also not recommended for people with heart disease, high blood pressure, an overactive thyroid gland, glaucoma, or for people who are pregnant or breastfeeding. It’s important to tell your provider about any other prescription or over-the-counter (OTC) medications you’re currently taking before starting either Wegovy or phentermine.  

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Which Weight Loss Medication is Right For Me?

Wegovy and phentermine can help people lose weight. However, they work in different ways and have different side effects. It’s important to talk to your healthcare provider before starting either medication to ensure it’s right for you.

Wegovy is best for those who want to lose a significant amount of weight and improve their metabolic health. Behavioral modifications are essential to treatment with Wegovy, and you’ll need to be committed to changing your diet, exercise habits, and stress management.

Phentermine is best for those who want to kickstart their weight loss journey and lose a few pounds quickly. Phentermine is not meant as a long-term solution, and you may need to take it for only a few weeks or months before tapering off.

If you’re struggling to lose weight on your own, medication may help. Wegovy and phentermine are two options that can boost weight loss. However, these medications are not for everyone and have potential side effects. Talk to your healthcare provider about which weight loss medication is right for you.

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Frequently Asked Questions

Is semaglutide better than phentermine for weight loss?
Semaglutide and phentermine are two different medications used to support weight loss. In higher doses, Wegovy (semaglutide) can support sustained weight loss with long-term use. Phentermine can also assist weight loss, but is only intended for short-term use.
What medication is comparable to Wegovy?
Wegovy is a type of medication called glucagon-like peptide-1 (GLP-1). It contains the active compound semaglutide. Another GLP-1 medication that contains semaglutide is called Ozempic, but it contains smaller doses of semaglutide and is primarily used as a medication for type 2 diabetes. Examples of other GLP-1s include liraglutide (Saxenda) and dulaglutide (Trulicity).
How much weight can you lose on Wegovy?
According to clinical trial results cited by the FDA, people who take Wegovy lose an average of 6-12% of their body weight.
What are the risks of GLP-1 agonists for weight loss?
For most people who meet the BMI and health criteria for taking GLP-1s for weight loss, the medications are generally safe to use. The most common side effects are gastrointestinal, including nausea, vomiting, and diarrhea. However, people with a personal or family history of medullary thyroid cancer (a rare and primarily genetic type of thyroid cancer) and people with a rare condition called multiple endocrine neoplasia syndrome type 2 (MEN 2) should not take GLP-1s.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Terez Malka, MD

Dr. Terez Malka is a board-certified pediatrician and emergency medicine physician.