Ozempic vs. phentermine: which is better for weight loss?

Phentermine is approved by the US Food and Drug Administration (FDA) for weight management. While Ozempic is not FDA-approved for weight loss, it can be used off-label for weight loss. 

Studies suggest Ozempic is generally more effective, but phentermine may be a good option in some cases. 

So, how else do they compare? Keep reading for a breakdown of Ozempic vs. phentermine. 

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Ozempic is usually more effective than phentermine for weight loss, with people losing about 15 pounds in nine months at the highest dose of Ozempic. 

Semaglutide (the active ingredient in Ozempic and Wegovy) also offers cardiovascular benefits. Phentermine has heart-related risks, which can be an important difference to consider. 

But phentermine may be a better option in some cases, such as for those who prefer a pill over an injection or who want a more affordable drug. 

Here's a quick overview of the two medications:

1. Ozempic is an injection, while phentermine is a pill.

2. Ozempic is taken weekly; phentermine is taken daily.

3. Ozempic is a GLP-1 agonist, and phentermine is a stimulant.

4. Ozempic is typically longer-term, and phentermine is usually short-term.

5. Ozempic can be used off-label for weight loss; phentermine is approved for weight loss. 

6. Ozempic can help you lose a higher amount of weight compared to phentermine.

7. Ozempic can cause digestive issues; phentermine can cause heart and nervous system issues. 

8. Ozempic is a brand-name drug that can be costly, while phentermine is a generic medication, which means it’s typically lower in price. 

9. Ozempic is not habit-forming; phentermine carries a low risk of abuse and dependence and, as such, is a Schedule IV controlled substance.

Since Ozempic and phentermine belong to different drug classes and work in distinct ways, it’s not surprising that their possible side effects differ. 

When used incorrectly, both Ozempic and phentermine can potentially be dangerous for your health. It’s important to take only the dose prescribed by your healthcare provider, so they can monitor you for some of the more serious complications. 

Ozempic can cause kidney and gallbladder concerns, dehydration, low blood sugar (if taken with certain diabetes medications), pancreatitis, and severe stomach problems. There have also been reports of pulmonary aspiration (stomach contents entering the lungs) during surgery requiring sedation in people taking Ozempic. 

Phentermine is a stimulant and is considered a controlled substance. It can lead to dependence and abuse, especially in higher doses. There is also a risk of developing heart problems like heart valve disease and high blood pressure in the lungs, known as pulmonary hypertension. 

Other side effects are possible with either medication. Reach out to your healthcare provider or seek medical care if side effects don’t go away or seem severe.

Ozempic side effects

The most common side effects of Ozempic include: 

• Nausea

• Vomiting 

• Diarrhea

• Stomach pain

• Constipation

You may notice a theme here — these common side effects are all related to gastrointestinal issues. This makes sense, since Ozempic affects how we digest food.

Phentermine side effects

While Ozempic’s side effects primarily relate to its impact on digestion, phentermine’s side effects are largely related to its being a mild stimulant. Possible side effects of phentermine include: 

• Nervousness and excitability

• Insomnia

• Headache

• Dry mouth or thirst

• Dizziness

• Fast heart rate 

• Increase in blood pressure

• Palpitations

• Nausea

• Constipation 

• Erectile dysfunction

• Changes in libido

These effects are similar to some of the effects of other stimulants, such as amphetamines (e.g. Adderall).

Ozempic can help you lose more weight than phentermine, based on results from separate studies. 

Ozempic and phentermine haven’t been directly compared in head-to-head clinical trials. But when used along with a nutritious diet and regular exercise, either one can be quite effective for weight loss. Everyone is different, so the amount of weight loss will vary from person to person.  

Ozempic’s effectiveness: 

• In a trial for type 2 diabetes, people taking 1 mg of Ozempic lost about 13 pounds after about nine months, while those taking 2 mg lost about 15 pounds in the same timeframe.  

• In studies for type 2 diabetes, people taking 0.5 mg or 1 mg of Ozempic lost 5%–7% of their starting body weight after 7–12 months.

• In a trial for obesity, people taking 2.4 mg of semaglutide (the highest dose of Wegovy) lost about 15% on average over 68 weeks. The participants in this study did not have diabetes.

Phentermine’s effectiveness: 

• Weight loss with phentermine largely depends on the dose and the duration of use.

• It’s only FDA-approved for short-term use, but longer use may work better.

• In an analysis of six studies lasting 2–24 weeks, people taking phentermine lost about 8 pounds more than those on placebo. On average, people taking the drug lost about 14 pounds. 

• One study found taking phentermine led participants to lose at least 5% of their body weight loss after six months. 

To put it in perspective, weight loss medications are generally considered successful if you lose more than 5% of your body weight after 12 weeks of treatment with the recommended dosage. 

So really, either medication can be effective for weight loss. 

• Ozempic typically leads to a more substantial reduction in body weight. 

• Phentermine may help people lose weight more quickly (within a few weeks).

Phentermine is an older medication. It was FDA-approved for weight loss in 1959 for short-term use, based on less clinical data than what’s required for newer weight loss drugs. It may also stop working after a while — some people can develop a tolerance to its appetite-suppressing effects.

Despite its short-term approval, there have been some longer-term studies. Recent observational research of nearly 14,000 adults found the following results:

• People who used phentermine for more than a year lost significantly more weight — about 7.4% more at two years — than those who used it for 3 months or less.

• Those who took phentermine long-term did not have an increased risk of heart problems or death.

These results and other evidence suggest that long-term phentermine may be safe in low-risk individuals. As such, some healthcare providers may prescribe it long-term or on an intermittent schedule (e.g. several weeks “on” then several weeks “off”). But it depends on their professional judgement and your medical history. 

Ozempic tends to cost more than phentermine. This is because: 

• Ozempic is only available as a brand-name medication, while phentermine comes in a generic version.

• Ozempic is given by injection, and phentermine is available as a tablet

• Insurance likely won’t cover Ozempic for weight loss alone because it’s not specifically FDA-approved for this use. 

Weight loss medications are rarely covered by insurance. 

Without insurance, phentermine can cost less than $10 a month (depending on the pharmacy). 

Ozempic, on the other hand, can cost about $1,000 a month out-of-pocket. 

But if you take Ozempic for type 2 diabetes, your insurance may cover it. You can ask your healthcare provider for Wegovy instead, which contains the same active ingredient as Ozempic but is FDA-approved for weight loss and has a higher maximum dose.   

The Ro Body membership includes insurance verification to take the stress out of navigating insurance coverage. The manufacturer of Ozempic, Novo Nordisk, also offers a savings program if you’re eligible.

Ozempic and phentermine are safe for most people, but these medications aren’t right for everyone. 

Who shouldn’t take Ozempic?

Don’t take Ozempic if you are nursing, pregnant, planning to  become pregnant, or if you have:

• A certain type of thyroid cancer, called medullary thyroid carcinoma (MTC) or a family history of MTC 

• Multiple endocrine neoplasia type 2 (MEN 2), a disorder that causes tumors in the thyroid and other glands

If you have certain health conditions, Ozempic can make them worse. Your healthcare provider might recommend extra monitoring or using a different medication altogether if you have: 

• Pancreatitis

• Diabetic retinopathy

• Gallbladder disease

• Digestive problems, such as severe gastroparesis

•  Upcoming surgery that requires sedation

Ozempic may also lead to hypoglycemia (low blood sugar) when combined with insulin or certain diabetes pills (such as glimepiride).

Who shouldn’t take phentermine?

If you are pregnant, nursing, or have a history of any of the following, you shouldn’t take phentermine: 

• Heart disease (including high blood pressure, coronary artery disease, heart attack or stroke, or congestive heart failure)

• Hyperthyroidism

• Glaucoma

• Drug abuse or substance use disorder

• Agitation (a possible symptom of some mental health conditions)

You shouldn’t use phentermine with alcohol. Don’t use phentermine while taking or within 14 days of stopping an MAOI (monoamine oxidase inhibitor) because it can cause dangerously high blood pressure. 

It’s possible to take Ozempic and phentermine together if your healthcare provider prescribes both. It’s unknown if using the two together is safe or leads to more weight loss, since the combination hasn’t been studied. 

Ozempic and phentermine aren’t known to interact with each other. But according to the prescribing information for phentermine, it’s not recommended to take it with other weight loss medications. 

But your healthcare provider might prescribe both if that’s your best option. There are a few things to keep in mind. 

• You’ll likely start on one medication initially. Since semaglutide works well for weight loss, your healthcare provider may not add phentermine. Instead, you may have your semaglutide dose increased. 

• You might add another if needed. If you aren’t seeing the weight loss you need, your healthcare provider might add the second medication to potentially get better results. 

• But taking the medications together can increase side effects. The more medications you take, the more chances there are for side effects. You may tolerate both medications just fine, but let your provider know if you’re experiencing uncomfortable side effects.

There are many other medications that can help with weight management, all with their different effectiveness, side effects, and costs. 

Some of the most common weight loss alternatives to Ozempic and phentermine include: 

• Wegovy (semaglutide): Unlike Ozempic, Wegovy is FDA-approved for weight loss and is a GLP-1 medication injected weekly.

• Zepbound (tirzepatide): A GLP-1 and glucose-dependent insulinotropic polypeptide (GIP), Zepbound is FDA-approved for weight loss and works similarly to other GLP-1s. 

• Saxenda (liraglutide): A GLP-1 receptor agonist, it’s FDA-approved for weight loss, given as a daily injection.

• Qsymia (phentermine/topiramate): A combination medication taken as a daily capsule, Qsymia works better than either medication alone to control overeating and reduce appetite. Unlike phentermine alone, Qsymia is FDA-approved for long-term weight management.

• Contrave (naltrexone/bupropion): A combination medication, Contrave is a daily tablet approved for weight management to decrease cravings and appetite. Side effects can include nausea, constipation, and headache.

• Orlistat (Xenical, Alli): Available as both a prescription (Xenical) and over-the-counter formulation (Alli), orlistat is a medication that blocks fats you eat from being absorbed. It’s a capsule taken three times a day with meals. It can cause fatty stools and diarrhea. 

Wegovy, Saxenda, and Zepbound are GLP-1 medications that tend to cause more weight loss than oral weight loss medications, including Qsymia, Contrave, and orlistat. But the flip side is they tend to be higher in cost.

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Both Ozempic and phentermine can be used for weight management. But they differ in their FDA-approved uses, how they work, side effects, effectiveness, and more. Here’s what to keep in mind:  

• Ozempic is a weekly injection that’s FDA-approved for people with type 2 diabetes, but it can also reduce your appetite and promote significant weight loss. Because of this, Ozempic is often prescribed off-label for weight loss. 

• Phentermine is an oral pill that can suppress appetite, but it isn’t safe for some people. It’s a mild stimulant that can affect heart rate and blood pressure. It’s specifically approved for short-term weight loss. 

• Other key differences between Ozempic and phentermine include their overall effectiveness, their side effect profiles, and their cost. Ozempic typically leads to greater weight loss, can lead to gastrointestinal side effects, and tends to be more expensive compared to phentermine.