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 (semaglutide) is not FDA-approved for weight loss, it can be used off-label for weight loss. 

Research suggests Ozempic generally results in more weight loss, but phentermine may be a good option in some cases. Below is a full breakdown of Ozempic vs. phentermine for weight loss.

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) also offers cardiovascular benefits. Phentermine has heart-related risks, which can be an important difference to consider.

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Phentermine may be a better option in some cases, such as for those who want a more affordable medication. Phentermine is available as a daily pill. As of May 4, 2026, the pill form of semaglutide under the brand name Rybelsus has been rebranded to the Ozempic pill. Ozempic is available as an injection and as a daily pill.

Here's a quick overview of the two medications:

1. Ozempic is both an injection and pill, while phentermine only comes as a pill.

2. Ozempic is taken weekly or daily depending on the form; 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 is associated with greater weight loss compared with 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 risk of abuse and dependence and, as such, is a Schedule IV controlled substance.

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

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

Ozempic side effects

The most common side effects of Ozempic include: 

• Nausea

• Vomiting 

• Diarrhea

• Stomach pain

• Constipation

• Dehydration

• Low blood sugar (if taken with certain diabetes medications)

• Kidney and gallbladder concerns

• Pancreatitis

• 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 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 or palpitations

• Increase in blood pressure

• Nausea

• Constipation 

• Erectile dysfunction or changes in libido

• Dependence and abuse, especially in higher doses

• Heart problems like heart valve disease

• High blood pressure in the lungs, known as pulmonary hypertension

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

Other side effects are possible with either medication. Contact a healthcare provider or seek medical care if side effects do not resolve or seem severe.

Ozempic can lead to greater weight loss than phentermine, based on results from separate studies.

Ozempic and phentermine have not been directly compared in head-to-head clinical trials. When used alongside a nutritious eating plan and regular exercise, either can be effective for weight loss. Individual results will vary.

Ozempic’s effectiveness

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

• In a trial that included people with type 2 diabetes, those 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 various 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 (Wegovy) lost about 15% of body weight on average over 68 weeks. The participants in this study did not have diabetes.

Phentermine’s effectiveness

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

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

• It is only FDA-approved for short-term use, based on less long-term clinical data than what is typically required for newer weight loss medications.

• Longer use may work better. 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, with no increased risk of heart problems or death.

• 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 that taking phentermine led participants to lose at least 5% of their body weight after six months. 

• It may stop working after a while — some people can develop a tolerance to its appetite-suppressing effects.

To put this in perspective, weight loss medications are generally considered successful when a person loses more than 5% of body weight after 12 weeks of treatment at the recommended dosage.

Some healthcare providers may prescribe phentermine long-term or on an intermittent schedule (e.g., several weeks "on" then several weeks "off"), depending on professional judgment and the individual's medical history.

The cash price of Ozempic can be about $1,000 a month for injections and about $200–$300 a month for the oral tablet. The cash price of phentermine can be as low as $10 a month (depending on the pharmacy).

Ozempic tends to cost more than phentermine. Reasons for this include: 

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

• Ozempic is available by injection as well as tablet, and phentermine is available as a tablet only.

• Insurance likely will not cover Ozempic for weight loss alone because it is not specifically FDA-approved for this use.

For those taking Ozempic for type 2 diabetes, insurance may cover it. A healthcare provider can advise on whether Wegovy may be an appropriate alternative — it 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 simplify navigating coverage.

Ozempic and phentermine are safe for most people, but these medications are not right for everyone.

Who shouldn’t take Ozempic?

Ozempic should not be taken by those who are nursing, pregnant, planning to become pregnant, or who have any of the following:

• 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

Certain health conditions may be worsened by Ozempic. A healthcare provider might recommend extra monitoring or a different medication altogether for those with:

• 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?

Phentermine should not be taken by those who are pregnant, nursing, or have a history of any of the following:

• 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)

Phentermine should not be used with alcohol. It should not be taken while taking or within 14 days of stopping an MAOI (monoamine oxidase inhibitor), as this can cause dangerously high blood pressure.

It is possible to take Ozempic and phentermine together if a healthcare provider prescribes both. It is unknown whether using the two together is safe or leads to greater weight loss, since the combination has not been studied.

Ozempic and phentermine are not known to interact with each other. However, according to the prescribing information for phentermine, taking it with other weight loss medications is not recommended.

A healthcare provider might still prescribe both if that is the best option. A few things to keep in mind:

• Starting on one medication initially is typical. Since semaglutide works well for weight loss, a healthcare provider may not add phentermine — the semaglutide dose may be increased instead.

• A second medication may be added if needed. If weight loss results are insufficient, a healthcare provider might add the second medication to potentially improve outcomes.

• Taking the medications together can increase side effects. The more medications taken, the greater the chance of side effects. Both may be well tolerated, but a healthcare provider should be informed of any uncomfortable side effects.

There are many other medications that can help with weight management, each with 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 or taken as a pill every day.

• 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 lead to greater weight loss than oral weight loss medications, including Qsymia, Contrave, and orlistat — though they tend to have a higher cash price.

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Both Ozempic and phentermine can be used for weight management, but they differ in their FDA-approved uses, mechanisms, side effects, and effectiveness.

• Ozempic is a weekly injection or daily pill FDA-approved for people with type 2 diabetes, but it can also reduce 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 is not safe for some people. It is a mild stimulant that can affect heart rate and blood pressure. It is 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.