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Drug vs. Drug

Phentermine vs. Ozempic: Differences, similarities, and which one is better for you

Phentermine and Ozempic are two common medications for weight loss, with different mechanisms, side effects, and costs
Karen Berger medical writer and reviewer headshot
By | Updated on Oct. 1, 2024
Rx pills compared: Phentermine vs. Ozempic:

Key takeaways

  • Phentermine is a weight loss drug taken by mouth one to three times daily, depending on the dose. Ozempic (semaglutide), a GLP-1 agonist approved for Type 2 diabetes management and prescribed off-label for weight loss, is injected once a week.

  • Common side effects of phentermine include dry mouth and increased heart rate, while Ozempic is often associated with gastrointestinal issues like nausea and diarrhea.

  • Phentermine can lead to a 4.4% weight loss over 28 weeks, while semaglutide is considered more effective, averaging 15% weight loss over 68 weeks. It is often preferred over phentermine for weight loss when lifestyle changes are not enough.

  • Phentermine is less expensive and may not be covered by insurance. Ozempic can be more costly but may have insurance coverage, depending on the condition being treated.

In this article:

Phentermine and Ozempic are commonly prescribed for weight loss. Phentermine, which is classified as a sympathomimetic amine, is approved by the United States Food and Drug Administration (FDA) for short-term use for weight loss. It is a Schedule IV controlled substance, because it has the potential for abuse and dependence. Phentermine is a stimulant that works similarly to amphetamines (such as Adderall). It is thought to promote weight loss through various mechanisms, including effects on the central nervous system, metabolic changes, and suppressing appetite. 

Ozempic contains the active ingredient semaglutide and is injected subcutaneously (under the skin) every week. Ozempic is classified as a glucagon-like peptide-1 (GLP-1) agonist. It is FDA approved to help control blood sugar in adults with Type 2 diabetes. It is also FDA approved to lower the risk of major adverse cardiovascular events (such as heart attack, stroke, and death) in adults with both Type 2 diabetes and cardiovascular disease. Although Ozempic is not FDA approved for weight loss, healthcare providers often prescribe it off-label for this use. Off-label prescribing means that a drug is prescribed for a use that is not FDA-approved. Ozempic helps with weight loss by delaying stomach emptying, which helps regulate appetite. 

While both medications are commonly prescribed to help people lose weight, they differ in several ways, including their active ingredients, how they are taken, and their side effects. Keep reading to learn more about phentermine and Ozempic.

What are the main differences between phentermine and Ozempic?

Phentermine is a sympathomimetic amine that is generally taken by mouth once daily in the morning. Alternatively, a lower dose may be taken three times daily. It is available in both brand and generic forms, although the 8 mg dose is only available as a brand-name drug. Ozempic is a brand-name GLP-1 receptor agonist that contains the active ingredient semaglutide. It is injected once weekly, with a dose that is gradually increased under the supervision of a healthcare provider. 

Main differences between phentermine and Ozempic
Drug class Sympathomimetic amine GLP-1 agonist
Brand/generic status Brand and generic Brand
What is the generic name?

Or

What is the brand name?

 Brand names include Adipex-P and Lomaira There is no generic available. The active ingredient is called semaglutide.
What form(s) does the drug come in? Oral tablet: 8 mg, 37.5 mg

Oral capsule: 15 mg, 30 mg

 Injection 
What is the standard dosage? 15 to 37.5 mg by mouth once daily in the morning;

or 8 mg by mouth three times daily, 30 minutes before meals

 Starting dose of 0.25 mg injected subcutaneously once weekly, gradually increasing to 1 mg or 2 mg weekly under healthcare provider guidance
How long is the typical treatment? Short-term use Long-term use
Who typically uses the medication? Adults Adults

Conditions treated by phentermine and Ozempic

Phentermine is FDA approved for short-term use as a weight loss treatment, typically for several weeks, though some healthcare providers may prescribe it for longer with close monitoring. It can be used in people with obesity (with a body mass index, or BMI, of 30 or higher); or people with overweight (BMI of 27 or higher) who also have other weight-related health conditions such as high blood pressure or high cholesterol.

Ozempic is prescribed to improve blood sugar control in adults with Type 2 diabetes mellitus. It can also be used to lower the risk of heart attack, stroke, and cardiovascular death in adults with both Type 2 diabetes and heart disease. Ozempic is also prescribed off-label (for a non-FDA approved use) for weight loss. 

Both phentermine and Ozempic are generally recommended along with lifestyle changes like a reduced calorie, balanced diet, and increased physical activity. 

Note that Ozempic contains the active ingredient semaglutide. Other medications contain semaglutide, but have various approved uses, including Wegovy (a weekly injectable medicine) and Rybelsus (a daily oral medication). Wegovy is FDA approved for chronic weight management. Wegovy can also be used to lower the risk of heart attack, stroke, and cardiovascular death in adults with both heart disease and overweight or obesity. Rybelsus is used for Type 2 diabetes blood sugar management.

Condition Phentermine Ozempic
Weight loss  Yes  Off-label
Type 2 diabetes No  Yes 
Cardiovascular risk  No  Yes 

Is phentermine or Ozempic more effective?

There are no direct studies comparing the effectiveness of phentermine and Ozempic for weight loss. However, we can examine their individual results. 

Phentermine typically results in an average weight loss of about 4.4% of body weight over 28 weeks, although some healthcare providers may not prescribe it for that long. 

In contrast, clinical studies show that people taking semaglutide 2.4 mg once weekly (available as Wegovy, but similar to a 2 mg weekly dose of Ozempic) experienced an average weight loss of 15% over 68 weeks.

Obesity is considered a chronic medical condition. If lifestyle changes alone do not lead to significant weight loss, experts often recommend adding medication to support these interventions. While some experts and guidelines advise against phentermine, others recommend it in specific situations. In most cases, semaglutide is favored over other weight loss medications due to its benefits. Although the 2.4 mg semaglutide dose is specific to Wegovy, using Ozempic off-label at 2 mg weekly is expected to result in similar effects.

Both medications can have side effects. Phentermine may cause unpleasant symptoms like heart palpitations and dry mouth, while Ozempic is often associated with gastrointestinal issues such as nausea and diarrhea.

Ultimately, the best medication for you should be determined by your healthcare provider, who can consider various factors to identify the best treatment for your condition.

Coverage and cost comparison of phentermine vs. Ozempic

Insurance and Medicare prescription plans generally do not cover phentermine. Many plans will cover Ozempic, but insurance coverage and copays vary. Some plans may require prior authorization, meaning the healthcare professional must provide an explanation to the insurance company for why the medication should be covered. While some plans will pay for Ozempic when prescribed for Type 2 diabetes, they may not cover it when prescribed for weight loss. You can contact your insurance plan for more information and up-to-date pricing estimates.

If you pay out of pocket for a one-month supply of phentermine, you would typically pay about $49. However, if you use a free phentermine coupon discount card at a participating pharmacy, you could pay as low as $6.

Paying out of pocket for a one-month supply of Ozempic could cost about $1,317. A free Ozempic discount card could reduce the price to as low as $788.

Phentermine vs. Ozempic costs
Phentermine Ozempic
Typically covered by insurance? No  Varies 
Typically covered by Medicare Part D? No  Varies 
Quantity #30, 37.5 mg tablets 1 box of 4, 2 mg pens
SingleCare cost $6+ $788+

Common side effects of phentermine vs. Ozempic

Common potential side effects of phentermine may include:

  • Dry mouth or altered taste
  • Stomach problems (constipation or diarrhea)
  • Heart palpitations or fast heart rate
  • Dizziness
  • Shaking (tremors)
  • Headache
  • Sexual problems
  • Increased blood pressure
  • Restlessness or overstimulation
  • Difficulty sleeping
  • Mood changes (euphoria or dysphoria)
  • Psychosis (disconnection from reality, including hallucinations or delusions)

Ozempic is generally associated with gastrointestinal issues. The most common potential side effects of Ozempic may include:

  • Nausea
  • Vomiting
  • Diarrhea or constipation
  • Stomach pain

With any drug, including phentermine or Ozempic, allergic reactions are rare. If you have symptoms such as hives, difficulty breathing, or swelling of the face, lips, tongue, or throat, you should get emergency medical attention right away. 

This is not a full list of side effects, and others may occur. Consult your health care provider or pharmacist for more information about side effects.

Drug interactions of phentermine vs. Ozempic

Before taking phentermine or Ozempic, tell your healthcare provider about all the medications you take, including prescription and OTC drugs, vitamins, and supplements. 

If you take a monoamine oxidase inhibitor drug class (MAOI), you should avoid taking phentermine during MAOI treatment and for 14 days after the last dose. Phentermine may also interact with other medications such as insulin, oral diabetes medications, and SSRI antidepressants. You should avoid alcohol while taking phentermine, as alcohol can cause or worsen side effects of phentermine.

Ozempic can interact with insulin as well as certain types of oral diabetes medication known as sulfonylureas, possibly causing hypoglycemia (low blood sugar). A lower dose of insulin or oral diabetes medicine may be required. Ozempic slows stomach emptying, which could possibly affect the absorption of oral medications if taken around the same time. While clinical studies did not find a significant impact on absorption, it is still a good idea to ask your healthcare provider if you should adjust the timing of any medications. If you drink alcohol, consult your healthcare provider before combining it with Ozempic. While there is no direct interaction, alcohol can cause low blood sugar and may worsen the side effects of Ozempic.

Not all drug interactions will require you to avoid one or the other medicine. Some interactions may require close monitoring and/or a dosage adjustment. Talk to your healthcare provider about drug interactions and how they may affect you. 

Drug Drug Class Interacts with phentermine? Interacts with Ozempic?
Phenelzine 

Rasagiline 

Tranylcypromine 

 Monoamine oxidase inhibitors Yes  No 
Insulin  Insulin  Yes  Yes 
Januvia

Jardiance

Metformin

 Oral diabetes medicines Yes  Certain oral diabetes medications known as sulfonylureas  (glimepiride, glipizide, and glyburide) interact with Ozempic
Fluoxetine

Paroxetine

Sertraline

 SSRI antidepressants Yes  No 

Warnings of phentermine and Ozempic

Before taking phentermine or Ozempic, be sure to inform your healthcare provider about your medical conditions and family history. These medications are not safe for everyone, and certain medical conditions may make them unsafe for you. Let your healthcare provider know if you are pregnant, planning to become pregnant, or breastfeeding. Phentermine should not be used during pregnancy or while breastfeeding. For Ozempic, you should stop taking it at least two months before planning a pregnancy, as this medication takes a long time to completely leave the body. If you are pregnant or breastfeeding, follow your healthcare provider’s advice. Ozempic is generally not recommended in these situations unless your healthcare provider determines that the benefits outweigh the risks.

Phentermine warnings

  • Phentermine should not be used with other weight loss medications, including over-the-counter or herbal products.
  • In rare cases, primary pulmonary hypertension (high blood pressure in the lungs) may occur. If you experience shortness of breath, chest pain, fainting, fluid retention in the legs or feet, or difficulty exercising, tell your healthcare provider right away.
  • Phentermine may be associated with an increased risk of heart disease. Discuss your risk factors with your healthcare provider.
  • As a controlled substance, phentermine has a risk of abuse and dependence. You should discuss this risk with your healthcare provider.
  • Do not drive or operate machinery until you know how phentermine affects you.

Ozempic warnings

  • Ozempic has a black box warning, the most serious warning required by the FDA. In animal clinical studies, semaglutide has caused thyroid tumors. It is not known if this applies to humans. People who have a history or family history of medullary thyroid carcinoma (MTC), or people with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) should not take Ozempic. Anyone who takes Ozempic should be alert to symptoms of thyroid cancer, such as difficulty breathing or swallowing, hoarseness, or a lump in the neck, and report any symptoms to the healthcare provider right away. 
  • Ozempic can cause serious side effects, including pancreatitis (inflammation of the pancreas), diabetic retinopathy, and gallbladder or kidney problems.
  • Ozempic pens should never be shared with anyone else, even if you change the needle. Make sure you understand how to use and dispose of the pen and needle properly. 

Frequently asked questions about phentermine vs. Ozempic

What is phentermine?

Phentermine is a prescription medication that is used for weight loss. It is generally used as a short-term treatment, although some people take it for longer periods if recommended by a healthcare provider. Phentermine is an oral medication that is taken by mouth. 

What is Ozempic?

Ozempic (semaglutide) is a once-weekly injectable prescription drug. It is FDA-approved for use in Type 2 diabetes, as well as to reduce cardiovascular risk in certain patients. However, it is often prescribed off-label (for a non-FDA-approved use) for weight loss. 

Are phentermine and Ozempic the same?

Phentermine and Ozempic are not the same. They contain different active ingredients, are administered differently (phentermine is taken by mouth, while Ozempic is injected), and have different side effects and warnings. The information above provides more details about each drug.

Is phentermine or Ozempic better?

Phentermine typically leads to about 4.4% weight loss over 28 weeks, while semaglutide (Ozempic) can result in approximately 15% weight loss over 68 weeks. Many experts recommend semaglutide for its greater effectiveness in weight loss, but it is best to consult your healthcare provider to determine the best option for you based on individual factors such as your medical conditions and weight loss goals.

Will I regain my weight after I stop taking Ozempic?

If you stop taking Ozempic, there is a possibility that you may regain weight. One study found that people who stopped taking semaglutide regained about two-thirds of the body weight they lost. To help maintain your weight loss, it is important to continue following healthy lifestyle changes, even after stopping the medication. Always consult your healthcare provider for guidance.

Can I use phentermine or Ozempic while pregnant?

Phentermine is not approved for use during pregnancy. Ozempic is generally not recommended during pregnancy unless specifically advised by your healthcare provider.

Can I use phentermine or Ozempic with alcohol?

The prescribing information for phentermine specifically warns against combining alcohol with this medicine. 

 

While Ozempic does not chemically interact with alcohol, drinking alcohol may lead to low blood sugar and can also worsen the side effects of Ozempic. Consult your healthcare provider for more information and medical advice.

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