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Weight Loss

23 min read

How does Wegovy vs phentermine compare for weight loss?

Written by Patricia Weiser, PharmD

Published: Jun 4, 2024

Medically Reviewed by Goldina Erowele, PharmD, MBA

Table of contents

Many weight loss medications are available, each with their own pros and cons. Two such medications are Wegovy (semaglutide) and phentermine (brand name: Adipex-P). While phentermine is the cheaper option, you may wonder if it’s as safe and effective as Wegovy. 

If you’re interested in learning more about Wegovy vs phentermine and how they work for weight loss, keep reading. Understanding the benefits and risks of each medication lets you make an informed decision on which is better for you.

Why wait to get started? Book an appointment today with a weight loss provider on Klarity and have an appointment in 24 hours or less.

Talk to a provider about Wegovy or phentermine in as little as 24 hours.

Wegovy vs phentermine: which leads to more weight loss?

While no clinical trials have directly compared Wegovy vs phentermine, available evidence from separate trials suggests that Wegovy leads to more weight loss than phentermine. 

In 1 recent study, 932 adults with obesity took phentermine once a day. About 80% of participants lost at least 5% of their starting body weight during the study. Participants lost an average of 15 to 19 pounds after 6 months. Note that phentermine is approved by the US Food and Drug Administration (FDA) for short-term use, up to 12 weeks — more about this later.

Wegovy, on the other hand, is approved for chronic (long-term) weight management. In clinical trials, 1,961 adults with obesity or overweight used Wegovy or placebo once a week and made lifestyle changes. On average, the Wegovy group lost 14.9% of their starting body weight after 68 weeks of treatment. The actual weight loss averaged close to 34 pounds. 

Experts categorize weight loss medications according to the effectiveness demonstrated across multiple clinical trials. Since phentermine leads to at least 3 to 5% weight loss, experts at the Endocrine Society put phentermine in the “greater weight loss” category. GLP-1 agonists, such as Wegovy, fall into the “robust weight loss” category of at least 5% body weight loss.

How do Wegovy and phentermine work for weight loss?

Wegovy and phentermine work differently in the body and belong to different drug classes.

Wegovy contains the active ingredient semaglutide, a glucagon-like peptide-1 (GLP-1) agonist medication. GLP-1 is a natural incretin hormone that helps regulate hunger by increasing satiety (fullness) after you eat. It also regulates blood sugar levels by stimulating the release of insulin. GLP-1 agonist medications work by mimicking the natural effects of the GLP-1 hormone. 

How does this lead to weight loss? GLP-1 agonist medications, like Wegovy, help you feel full more quickly and for longer. This reduces your appetite, or desire to eat. Paired with increased exercise and a reduced-calorie diet, Wegovy is an effective medication for weight loss and weight maintenance.

Phentermine causes weight loss through a different mechanism. It’s a stimulant, also known as an appetite suppressant. It works by stimulating the release of brain chemicals (neurotransmitters), such as norepinephrine, dopamine, and epinephrine. This neurotransmitter release leads to reduced appetite, causing you to eat less and resulting in weight loss. Phentermine also activates the nervous system and can give you a boost of energy that may help you exercise.

How else are Wegovy and phentermine different and similar?

Wegovy and phentermine are both weight loss medications, but they have several key differences. One example is how long they’ve been available in the U.S. Phentermine has been available since 1959, while semaglutide (the active ingredient in Wegovy and Ozempic) was first approved in 2017. Other key differences include their approved uses, dosages, and how they’re taken.

Wegovy vs phentermine: approved FDA uses  

When FDA approves a medication, the approval includes specific uses known as indications. The FDA and healthcare professionals typically use a measurement called body mass index (BMI) to determine if someone qualifies for a weight loss treatment. BMI is calculated using your weight and height. A BMI of 25 to 29.9 is considered overweight, while obesity is defined as having a BMI of 30 or greater.

Along with increased physical activity and a reduced-calorie diet, Wegovy is FDA-approved for 2 indications:

  • To reduce excess body weight and for long-term weight maintenance in adults and children age 12 or older with obesity, or in overweight adults with at least one weight-related condition such as heart disease, type 2 diabetes, or high blood pressure.
  • To lower the risk of major cardiovascular problems (such as heart attack or stroke) in adults with obesity or overweight and known heart disease. 

In contrast, Adipex-P (one brand-name version of phentermine) is FDA-approved for short-term weight loss alongside diet, exercise, and behavioral modifications. It’s meant for people age 16 or older who meet 1 of the following criteria:

  • BMI of 30 or greater (obesity). 
  • BMI of 27 or greater (overweight) with other health conditions, such as diabetes, high cholesterol, or controlled high blood pressure. 

Phentermine is meant for short-term use because the body develops a tolerance to it within a few weeks. Tolerance is when your body gets used to a medication so it no longer provides the same effects as when you first started. Healthcare providers can prescribe phentermine for long-term use if they feel it’s safe, meaning the benefits outweigh the risks. Doing so is an off-label use of phentermine. 

Phentermine vs Wegovy: forms and dosages

Other key differences between phentermine and Wegovy include how they’re taken and their dosing frequencies. 

Wegovy is an injectable medication given once a week. It’s best to take it on the same day each week, at any time of day. You inject it under the skin (subcutaneously) in your abdomen, thigh, or upper arm. There are 5 Wegovy doses, ranging from 0.25 to 2.4 milligrams. Your provider will most likely start at the lowest dose and gradually increase to the maximum tolerated dose — typically 1.7 or 2.4 milligrams once a week. 

Phentermine is an oral medication. The brand version, Adipex-P, is available as an oral tablet and capsule. Generic phentermine comes in 3 forms: an oral tablet, orally disintegrating tablet, and an oral capsule. The drug is available in multiple strengths ranging from 15 to 37.5 milligrams. You take it by mouth once a day, about 2 hours after breakfast. Avoid taking your phentermine dose late in the day as this can cause trouble sleeping.

Another difference is that, while it can be difficult to find Wegovy in stock, phentermine doesn’t face shortages. Pharmacies nationwide have had limited or no stock of Wegovy and other weight loss injections due to national drug shortages and increased demand. 

Comparing Wegovy and Phentermine

The table below highlights key differences between Wegovy and phentermine.

Wegovy (semaglutide)Adipex-P (phentermine)
Drug classGLP-1 agonistCNS stimulant, anorexiant
Controlled substanceNoYes
Short-term or long-term useLong-termShort-term
Generic availableNoYes
Active ingredientSemaglutidePhentermine
FDA-approved forWeight loss/weight maintenance in people ages 12+ with obesity
Weight loss/weight maintenance in people ages 12+ with overweight and at least 1 weight-related health condition
Reduce risk of cardiovascular events in obese or overweight adults with heart disease
Weight loss in people ages 16+ with obesity (BMI 30+)
Weight loss in people ages 16+ with overweight (BMI 27+) and at least 1 weight-related health condition
Minimum age1216
Dosage formInjectionOral pill
Taken how oftenOnce weeklyOnce daily
Common side effectsStomach upset
High blood pressure
Fast heart rate
Unpleasant taste
Average cost per month*$1,430$45 – $50
*Cost according to drugs.com, with their discount card, at time of publication. Actual cost may vary.

Wegovy vs phentermine, Which costs less?

When comparing the cost of Wegovy vs phentermine, phentermine is considerably cheaper. In fact, 28 months of phentermine costs around the same as 1 month of Wegovy. 

Wegovy retails for $1,430.01 per month regardless of dose, phentermine prices vary depending on form and dosage. The price of phentermine decreases slightly as the strength increases. Costs for a 30-day supply of phentermine are as follows, according to drugs.com with their discount card:

Phentermine DosePrice*
Phentermine 15 mg capsules$50.06, or $1.67 per capsule
Phentermine 30 mg capsules$48.21, or $1.61 per capsule
Phentermine 37.5 mg capsules$44.90, or $1.50 per capsule
*Cost according to drugs.com, with their discount card, at time of publication. Actual cost may vary. 

Why is phentermine so much cheaper than Wegovy? Phentermine was first approved in 1959 and is available as a generic drug. Generic medications are typically sold for much cheaper than brand-name options because of how costly it is to develop and test brand-name drugs. 

Unlike phentermine, Wegovy is only available as a brand-name medication, and generic versions aren’t yet approved by the FDA. One alternative to Wegovy is compounded semaglutide, available from compounding pharmacies or clinics that partner with compounding pharmacies.

If you’re looking to save on Wegovy with or without insurance, you may be eligible to get Wegovy for free with the Wegovy Savings Card, or get discounts using a Wegovy coupon

Wegovy vs phentermine: insurance coverage

Is insurance more likely to cover Wegovy or phentermine? It depends — there isn’t a clear yes or no answer. Insurance coverage depends on your specific health plan and which medications it covers (also known as a formulary list). One option may be cheaper than the other depending on your specific plan and drug co-pay. Contact your insurance provider to see what they cover and which option costs less for you. 

Some plans require their members to try phentermine or another less expensive medication before approving coverage for Wegovy. This is known as step therapy. It requires patients to see if a cheaper medication works. If not, then the plan lets you progress to a more expensive option, like Wegovy.

Though some insurance companies cover Wegovy and phentermine, they may require a prior authorization for Wegovy or phentermine before they do. A prior authorization is when your insurance company requires additional documentation stating that your healthcare provider thinks the treatment is medically necessary. Once your provider submits the request, your insurance company will review it and approve or deny based on medical necessity. If approved, they can decide to cover all or a portion of the medication cost. If you receive a prior authorization denial, you have the right to appeal it.

Wegovy vs phentermine: side effects and contraindications 

Like other medications, Wegovy and phentermine may cause side effects. Wegovy’s side effects tend to be gastrointestinal (digestion-related), while phentermine’s tend to be cardiac (heart) or neurological (brain and nerves). 

Wegovy side effects are usually worse when you start taking it and when you increase your dose, but they typically ease with time. In contrast, phentermine’s side effects may persist for as long as you take it and may become more severe over time.

Wegovy side effects and contraindications

Common side effects listed in Wegovy’s prescribing information include:

  • Nausea
  • Diarrhea
  • Vomiting
  • Constipation
  • Abdominal pain
  • Headache
  • Fatigue
  • Heartburn
  • Dizziness
  • Low blood sugar, especially if using insulin or certain other diabetes medications
  • Gas
  • Gastroesophageal reflux disease
  • Injection site reactions

Some people experience serious side effects when using Wegovy. These include acute pancreatitis, gallbladder disease, hypoglycemia, acute kidney injury, diabetic retinopathy, rapid heartbeat, and suicidal behavior or ideation. Serious allergic reactions are also possible.

Like other GLP-1 agonists, Wegovy has a boxed warning for the risk of thyroid cancer. In animal studies, semaglutide was shown to cause thyroid tumors in rodents. This risk hasn’t been identified in humans. Still, people who have an existing risk of thyroid cancer shouldn’t use Wegovy. This includes people with a family or personal history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN2). 

Phentermine (Adipex-P) side effects and contraindications

Side effects of phentermine may include:

  • Fast heartbeat
  • High blood pressure
  • Restlessness
  • Hyperactivity
  • Dizziness
  • Insomnia
  • Unpleasant taste
  • Dry mouth
  • Mood changes such as euphoria (feeling high) or dysphoria (feeling low)
  • Tremor
  • Headache
  • Sexual dysfunction
  • Diarrhea
  • Constipation

Rare but severe side effects of phentermine include primary pulmonary hypertension, valvular heart disease, and withdrawal symptoms. 

Phentermine is a controlled substance. Controlled substance medications are strictly regulated by the US Drug Enforcement Agency (DEA) due to their potential to cause misuse or dependence. Phentermine is a Schedule IV controlled substance, which means its risk of misuse and dependence is relatively low, but still possible. To help lower the chance of these problems, you shouldn’t take more phentermine than your healthcare provider prescribes.

Phentermine shouldn’t be taken by people with certain health conditions or factors, including:

  • History of cardiovascular disease, such as uncontrolled high blood pressure, arrhythmias, or coronary artery disease
  • Overactive thyroid
  • Glaucoma
  • Agitation
  • History of drug abuse
  • Current or recent use of monoamine oxidase inhibitors (MAOIs)
  • Pregnant or breastfeeding
  • Past allergic reaction to phentermine

Wegovy or phentermine for weight loss, which one to take?

When considering Wegovy vs phentermine, your decision depends on your health history and what matters most to you. Wegovy is more effective for weight loss. It’s also safer than phentermine for people with a history of high blood pressure or heart problems. Reasons to choose phentermine include cost and personal preference — phentermine is cheaper than Wegovy and is available as an oral pill, rather than an injection.

A healthcare provider will help you decide whether Wegovy vs phentermine, or another option, better aligns with your needs and weight loss goals.  

Key takeaway 

Wegovy (semaglutide) and phentermine (brand name: Adipex-P) are both effective weight loss medications, though they differ in how they work, available form, side effects, and cost. While no head-to-head studies have compared Wegovy vs phentermine for weight loss, available data suggests you can lose more weight with Wegovy.

Wegovy is a once-weekly injectable medication FDA-approved for weight loss and long-term weight maintenance. In contrast, phentermine is an oral pill approved for short-term weight loss (up to 12 weeks). Both medications are meant to be used alongside lifestyle changes, such as a low-calorie diet and regular exercise. 

Wegovy is much more expensive than phentermine. Four doses (1-month supply) of Wegovy retails for $1,430 on average, while phentermine costs up to $1.67 per pill. Due to its effectiveness and popularity, Wegovy is often in short supply. But you’re unlikely to have problems finding phentermine in stock.

Side effects are possible with both medications. Wegovy’s side effects tend to be digestion-related and temporary, while phentermine’s side effects affect the cardiovascular and nervous systems and may occur throughout treatment. Due to its potential for misuse, phentermine is considered a controlled substance.

The bottom line — both Wegovy and phentermine are effective for weight loss, but it’s important to be aware of other differences, such as safety and cost. Speak with a healthcare provider about your goals to determine if Wegovy vs phentermine is better for you.

Find a provider on Klarity and get the right weight loss med

Interested in Wegovy or phentermine for weight loss? Don’t wait. Find a provider on Klarity today to discuss medication options and get started on your weight loss journey. You can have a prescription for weight loss medication, like Wegovy or phentermine, in as little as 24 hours.

FAQs on phentermine vs Wegovy

How long does it take to lose weight on Wegovy or phentermine?

Wegovy is intended for long-term use. In clinical trials, people taking Wegovy lost an average of 15% body weight over 68 weeks. Phentermine is indicated for short-term use. An average 3 to 5% body weight reduction is typically seen within 12 weeks. Individual results vary.

Can you take Wegovy and phentermine at the same time?

There are no known drug interactions between Wegovy and phentermine. Since the medications work differently in the body, it’s possible to take both at the same time, but there isn’t scientific evidence to support the combination. The manufacturer of Adipex-P (phentermine) recommends not combining phentermine with other weight loss medications due to the lack of safety data. Wegovy’s manufacturer shared a similar warning when the drug was first approved, but it’s since been removed from the label. 

What is the difference between phentermine and semaglutide?

Phentermine and semaglutide are both weight loss medications, yet they work differently and have different risks to consider. They also differ in cost and how they’re taken. For example, phentermine is a generic oral capsule and Wegovy is a brand-name injectable medication. Phentermine is taken once a day, while Wegovy is once a week. Phentermine is a Schedule IV controlled substance that the body develops a tolerance to over time, and therefore is recommended for short-term use. Wegovy (semaglutide) isn’t a controlled substance and is effective for long-term weight maintenance.

Is there a better weight loss drug than Wegovy? 

Another popular weight loss medication is tirzepatide, sold as the brand name Zepbound. In one trial, participants taking Zepbound alongside lifestyle changes, like diet and exercise, experienced a weight reduction of up to 20.9%. Individual results vary, and many people reach their weight loss goals with different medications and treatments.

Does Ozempic work better than phentermine?

Probably, based on the weight loss results of separate studies. Ozempic and Wegovy have the same active ingredient semaglutide. But no head-to-head trials exist comparing Ozempic and phentermine. 


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The information provided in this article is for educational purposes only and should not be construed as medical advice. Always seek the guidance of a qualified healthcare professional with any questions or concerns you have regarding your health.

How we reviewed this article: This article goes through rigorous fact-checking by a team of medical reviewers. Reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the author.

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