Ozempic vs Phentermine for Weight Loss: Key Differences

Key Takeaways

• Ozempic is approved for diabetes management, while phentermine is approved for weight loss.
• Ozempic works by acting as a GLP-1 receptor agonist, which stimulates insulin production and improves satiety. On the other hand, phentermine stimulates the central nervous system and suppresses appetite, though the exact mechanism is not fully understood.
• Phentermine is a controlled substance; Ozempic is not. Controlled substances are regulated by the government due to their potential for misuse or dependence.
• The retail price of Ozempic is much higher than that of phentermine, but insurance may cover the medications, which lowers the cost.
• Both medications have been shown to help with weight loss. When choosing the best option for you, it's essential to consider factors such as your health status, any underlying conditions, current medications, family medical history, and other relevant factors.

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Ozempic and phentermine can both be prescribed for weight loss. The brand Ozempic (containing semaglutide) is FDA-approved to improve blood sugar control in people with diabetes, alongside diet and exercise. However, its off-label use for weight loss is becoming increasingly popular.

While phentermine is approved for weight loss alongside diet and exercise, it is only for short-term use. Phentermine is a generic medication sold under brand names such as Adipex-P, Lomaira, Fastin, and Ionamin.

Although they can be prescribed for the same purpose, they have many differences: how the drugs work, side effects, affordability, and effectiveness. Learning about these differences can help you choose the one that may be more suitable for you.

Phentermine and Ozempic Are Approved for Different Conditions

Phentermine and Ozempic are approved for different conditions. Ozempic is approved only for people with type 2 diabetes. Phentermine is approved for people with a body mass index (BMI) of 30 or higher or 27 or higher with risk factors such as controlled hypertension (high blood pressure), hyperlipidemia (high blood cholesterol), and diabetes.^{1, 2}

Another difference is how long these drugs can be used. While phentermine is only prescribed for short-term use, Ozempic can be prescribed for longer durations, depending on the individual treatment process.

Both Medications Work Differently

Ozempic contains semaglutide, which is a glucagon-like peptide-1 (GLP-1) receptor agonist. This means semaglutide acts as GLP-1. Your stomach naturally produces GLP-1 in response to food. When you eat, GLP-1 is synthesized, which then stimulates insulin production.

Therefore, semaglutide acts like GLP-1, helping to lower blood sugar levels by stimulating insulin production and inhibiting glucagon synthesis. This results in lower blood glucose levels and slows down food digestion, all of which signal your brain to stop eating. In other words, it decreases appetite or promotes satiety. In this way, it can reduce body weight, which is why it's prescribed as an off-label weight loss drug.^{2, 3}

On the other hand, phentermine is a sympathomimetic amine anorectic. It works by stimulating the central nervous system and suppressing appetite, but how it suppresses appetite is not yet clear.⁴

Phentermine and Ozempic Are Associated With Different Side Effects

Phentermine and Ozempic can cause side effects.

Ozempic’s Side Effects

Common side effects of Ozempic includes:²

• Nausea
• Vomiting
• Diarrhea
• Abdominal pain
• Constipation
  

However, Ozempic can also cause serious side effects, including:

• Pancreatitis (inflammation of the pancreas)
• Vision changes
• Hypoglycemia (low blood glucose levels)
• Kidney problems
• Allergic reactions

Phentermine's Side Effects

Phentermine can also cause gastrointestinal side effects, including dry mouth, unpleasant taste, vomiting, diarrhea, and constipation. You should consult your healthcare provider if your symptoms are severe or do not go away.¹

Other serious side effects of phentermine include, but are not limited to:

• Hypertension
• Tachycardia
• Primary pulmonary hypertension
• Restlessness
• Dizziness
• Insomnia
• Chest pain
• Swelling of the ankles and legs

You should immediately report these adverse events to your doctor if you experience them.⁵

<div class="pro-tip"><strong>Also Read: </strong><a href=ozempic-vs-rybelsus>Ozempic vs Rybelsus: Which Is Better for You?</a>.</div>

Ozempic Is Not a Controlled Substance, Phentermine Is

Some drugs are called controlled substances because the government regulates them to prevent drug abuse. This is because they can cause dependence. 

While some controlled substances are illegal in the U.S., others, like phentermine, can only be prescribed by licensed medical professionals. However, controlled substances have prescription limitations depending on the schedule they are classified under to help prevent drug abuse. 

Phentermine is similar to amphetamine and can be addictive. Phentermine, as a Schedule IV drug, has a limited risk of physical and mental dependence. It can only be refilled 5 times within six months from the day it is prescribed. Phentermine shouldn't be used if there is a history of drug abuse.⁶

Phentermine Might Be More Affordable Than Ozempic

The price of Ozempic is about $968 for a 1.5 mL pen with doses of 0.25mg, 0.5mg, 1mg, or 3mg. However, people with insurance may benefit from lower prices.⁷ 

Ozempic can be less costly if your insurance covers it, but phentermine has lower prices even without insurance. Its exact cost depends on whether phentermine is generic, branded, sold alone, or combined with other ingredients, such as topiramate. However, phentermine alone can be less than $10 for a month's treatment.⁸

Phentermine and Ozempic May Get Different Insurance Coverage

According to the Novo Nordisk website (the manufacturer of the Ozempic), eligible people with private or commercial insurance may benefit from much lower prices, such as $25 for a 1- to 3-month supply. How much you pay depends on your coverage, and you can check this on the Ozempic website.^{7, 9}

If you have Medicare or Medicaid, you may also benefit from lower prices for Ozempic, depending on your insurance plan and your state. Ozempic also has a patient assistance program through which people with Medicare or no insurance may be eligible for zero-cost medication, depending on eligibility criteria such as income and residency.¹⁰

Commercial insurance or Medicaid may cover phentermine, depending on your plan and the state you live in.¹¹

How Much Weight You Can Lose With Ozempic vs Phentermine

The choice of drug may affect how much weight you will lose, but this is alongside many other factors, including genetics, age, diet, and exercise regimen. Here are some studies that report the amount of weight loss with either semaglutide or phentermine:

• A study involving 175 individuals showed that participants given semaglutide lost an average of 5.9% of their body weight (6.7kg) in 3 months and 10.9% (12.3kg) at 6 months. Participants with type 2 diabetes lost significantly less weight than those without type 2 diabetes.¹²
• Another study published recently (2025) also showed a weight loss of 11.1kg (11.7%) in people given semaglutide. In this study, people without diabetes lost slightly more weight than those with prediabetes or diabetes.¹³
• Phentermine has been shown to significantly reduce body weight by an average of 6.7kg and waist circumference by 6.2cm in people with a BMI of 25kg/m² or above.¹⁴ 
• Another study of phentermine also showed a weight loss of 5.4 kg (5.7%) in participants with an average BMI of 33.8 kg/m².¹⁵
  

However, no clinical study has directly compared these drugs to date. The amount of weight you may lose with one drug or another can depend on individual factors. You should consult your healthcare provider to learn about your options for weight loss medications.

Can You Take Phentermine and Ozempic Together?

Adipex (a branded form of phentermine) warns against taking phentermine together with other weight loss drugs. They do not recommend combining two weight loss drugs due to a lack of safety and efficacy information. Also, Ozempic delays gastric emptying, which can affect the absorption of phentermine.^{2, 5}

Besides, the effects of the Ozempic (semaglutide) and phentermine combination have only been shown in a couple of studies, which were either case studies or studies with small sample sizes. Therefore, the safety of the combination remains unknown.¹⁶

However, your healthcare professional can prescribe both medications based on your individual treatment plan.

Phentermine vs Ozempic: What to Consider

You need to be informed and consider many factors before using both Ozempic and phentermine, including:

1. Ozempic

Before taking Ozempic, you should know:²

• Semaglutide may increase the risk of developing thyroid tumors.
• Semaglutide is not recommended if you or your family members have had or have medullary thyroid carcinoma (a type of thyroid cancer) or multiple endocrine neoplasia syndrome type 2 (MEN 2).
• Inform your doctor if you have an allergy to semaglutide or any other ingredients the drug may contain.
• It can cause pancreatitis, hypoglycemia, diabetic retinopathy, and kidney issues. If you have ever had these conditions, inform your doctor.
• Inform your doctor about your medications, pregnancy plans, or your pregnancy or breastfeeding status. The drug should be discontinued 2 months before pregnancy.
• You should never share the Ozempic pen with anyone else, even when changing the needle.

2. Phentermine

Before taking phentermine, you should know:^{1, 5}

• You may have an allergy to phentermine or other ingredients the medication may contain.
• Inform your healthcare provider about your medications, chronic diseases, pregnancy, or breastfeeding status.
• Drinking alcohol alongside phentermine can cause adverse reactions.
• Phentermine may not be as safe as other medications for people aged 65 years and older.
• It can cause primary pulmonary hypertension.
• You can build a tolerance to phentermine, in which case it is advised to discontinue the medication.
• It may impair the ability to perform certain activities, such as driving a motor vehicle or operating machinery.
• It can cause drug abuse and dependency.
• An adjustment of the dose of hypoglycemic medications or insulin may be required in some individuals.
• A diet and exercise plan is recommended to get the most benefit from phentermine treatment.

Ozempic vs Phentermine: Which Is Better for You?

There are many FDA-approved weight management medications, including phentermine and semaglutide. Among these options, there are several factors to consider when choosing a medication: your current health status, medical conditions and medications, family medical history, lifestyle, treatment cost, treatment duration, potential benefits and risks, and more.¹⁷

However, be aware that although some medications containing semaglutide (Wegovy) are approved for weight loss, Ozempic is not. That being said, your healthcare provider can prescribe medications they believe will be best for your weight loss program, disease management, and overall health.

The Bottom Line

Weight loss medications are approved for different conditions, work in various ways, cause different side effects, and come with distinct precautions, contraindications, and risks. That's why it’s important to consult your healthcare provider to find the best medication for safety and effectiveness.

Learn More About Signos CGM 

Signos incorporates cutting-edge research and the proven power of continuous glucose monitoring. The data gleaned from the Signos app can help guide your health journey. Not sure if Signos is right for you? Take this quiz to find out! Interested in learning more about nutrition and healthy eating habits? Check out more articles on our blog.

<div class="pro-tip"><strong>Learn More: </strong><a href=what-happens-if-you-stop-taking-ozempic>What Happens if You Stop Taking Ozempic? Ozempic Withdrawal Explained</a>.</div>