Ozempic vs. Phentermine: 8 Differences for Weight Loss

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Phentermine (Adipex-P, Lomaira) is a weight-loss pill that's been around for over 60 years. It is an affordable and effective option to help people lose weight. In the last 5 years, a newer medication class has emerged to help with weight loss: glucagon-like peptide-1 (GLP-1) agonists.

Of these, Ozempic (semaglutide) is one option that has become so popular that it can be difficult to find. And it's often compared with medications like phentermine. But it's not approved for weight loss. How do Ozempic and phentermine compare? Here are eight differences between these medications that you should know.

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

Ozempic and phentermine come in different dosage forms. Ozempic is an injection, and phentermine is an oral pill.

Ozempic is available in a multi-dose, prefilled injection pen. There are three different Ozempic pens available: red label (0.25 mg and 0.5 mg), blue label (1 mg), and yellow label (2 mg). Ozempic is injected once weekly, on the same day each week. You can inject your dose subcutaneously (under the skin) on your stomach, thigh, or upper arm.

Phentermine is available as an oral capsule, a tablet, and an orally disintegrating tablet. The available doses can vary depending on the form. These forms are usually taken once a day. Lomaira, a lower-dose version of phentermine, is taken 3 times a day before meals.

2. Ozempic and phentermine have different approved uses

Ozempic is known for its effects on body weight, but it's not approved for weight loss. Phentermine is approved for weight loss - but for short-term use only.

Ozempic is FDA approved to treat Type 2 diabetes in adults. Experts recommend Ozempic as an option for people with diabetes who need help managing their weight. They also recommend it for people with both diabetes and heart disease to lower the risk of major cardiovascular events. Ozempic may also be approved for kidney-related benefits soon.

Phentermine is approved for weight loss in people ages 17 and older. It's meant to be taken short term (up to 12 weeks). But more recent research suggests that it may be OK to take phentermine for longer. So your prescriber may have you keep taking phentermine if it's still working for you. But some people develop tolerance to it after a while.

Phentermine is also available in a combination weight-loss pill called Qsymia. Qsymia combines phentermine with topiramate, an anti-seizure medication. Unlike phentermine on its own, Qsymia is approved for chronic weight management.

Good to know: Wegovy, a higher-dose version of Ozempic, is approved for weight loss. People with and without diabetes may be eligible for Wegovy to help them lose weight.

3. Ozempic and phentermine work differently to cause weight loss

Whether you're prescribed Ozempic or phentermine, people often say that they notice a decrease in their appetite. Both medications can have this effect, but they cause weight loss in different ways.

Ozempic acts like a natural gut hormone called GLP-1. It has several effects in the body that can help lower blood glucose (sugar) levels. A few can contribute to weight loss. These include Ozempic's effects on the appetite center of the brain. It also slows the movement of food out of the stomach.

Phentermine is a stimulant that has a chemical structure similar to amphetamine. It's thought to work by increasing the release of brain chemicals that play a role in regulating appetite.

With both medications, a reduced appetite can cause you to eat fewer calories. This may result in weight loss. But for best results, combine with a nutritious diet and regular exercise.

4. Ozempic and phentermine can cause different side effects

Another difference is that Ozempic and phentermine can cause different side effects. Ozempic's side effects primarily affect your digestive tract. Many common phentermine side effects are from its effects on blood vessels and the nervous system.

Common Ozempic side effects include nausea, vomiting, and diarrhea. These are often worse when starting Ozempic and after dose increases. For many people, they improve over time. But adjusting your diet can help make them less bothersome. Serious side effects include pancreatitis and gallbladder problems. These are not common but have been reported.

Common phentermine side effects include insomnia, headache, and tremors (shakiness). It can also potentially increase your blood pressure and heart rate. Heart valve problems and high blood pressure in the lungs are rare but have also been reported.

Potential side effects should be considered along with your health history. In some cases, Ozempic or phentermine may not be safe for you to take. For example, people with a history of pancreatitis shouldn't take Ozempic. And people with hyperthyroidism (an overactive thyroid) should avoid phentermine. Their heart rate may already be elevated.

5. Ozempic may be a safer option than phentermine if you have heart disease

Phentermine is contraindicated in people with heart disease. This means it should be avoided because of potential harm. Semaglutide, the active ingredient in Ozempic, has proven cardiovascular benefits for people with heart disease - with and without diabetes.

Phentermine can increase heart rate and blood pressure. This can have serious effects in people with heart disease. But more research is needed to understand this risk. Some studies have found decreases in blood pressure due to weight loss from phentermine. But to be safe, your prescriber may not recommend phentermine if you have heart disease.

Ozempic can be a good option for people with heart disease. It has been shown to lower the risk of major cardiovascular events in people with both Type 2 diabetes and heart disease. Wegovy is also approved for this benefit in certain people without diabetes.

6. Phentermine is a controlled substance, while Ozempic is not

Phentermine is a controlled substance, meaning it has a risk of misuse and dependency. Because of this, you can refill your prescription only 5 times within 6 months. After that, you'll need a new prescription. Prescriptions for noncontrolled medications, such as Ozempic, expire 12 months after they're written.

Phentermine is structurally similar to amphetamines. Amphetamines, such as Adderall (mixed amphetamine salts), are also controlled substances. But phentermine's risk of misuse and dependency is much lower than amphetamines'. In fact, one study didn't see these risks with phentermine at all.

If you have a history of a substance use disorder, your prescriber may recommend against taking phentermine. There are other weight-loss pills and injections that aren't controlled substances. These may be a better option.

7. Phentermine is available as a lower-cost generic, while Ozempic is a brand-name medication

Ozempic is available only as a brand-name medication. Phentermine is available as both a brand-name medication and lower-cost generics. This may make phentermine a more affordable option.

Ozempic generics likely won't be available until at least 2031. So if you see "generic Ozempic" or "generic semaglutide" for sale, it's not the real thing.

8. Ozempic and phentermine may be covered differently by your insurance plan

Ozempic and phentermine have different approved uses. So your insurance plan may cover them differently. If you have Type 2 diabetes, there's a good chance that Ozempic is covered. Weight-loss medications like phentermine are inexpensive, but they are often not covered.

If you don't have Type 2 diabetes, it may be more difficult to get your insurance plan to cover Ozempic. But if you're eligible for Wegovy and also have heart disease, you may be able to get Wegovy covered. Contact your insurance plan for more details.

If your insurance plan does cover Ozempic, a copay savings card can help with costs if you're eligible. If you don't have insurance, you may be able to qualify for a patient assistance program to access Ozempic at no cost.

How much weight can you lose with Ozempic or phentermine?

Phentermine studies show weight loss of 5% to 10% after 3 to 6 months in people considered to be overweight or obese. One observational study found a greater weight loss in people who have been taking phentermine for over 12 months. This was compared with people taking it for shorter periods of time.

During initial Ozempic clinical trials, people with Type 2 diabetes who received the 1 mg Ozempic dose lost about 10 lbs after 30 weeks (7 months). The 2 mg (highest) dose has been shown to result in about 15 lb of weight loss after 40 weeks (9 months). But it's not unusual for people taking Ozempic to report losing even more weight.

Is Ozempic safe for weight loss?

Generally, yes. Ozempic's active ingredient, semaglutide, has been studied for weight loss in people with and without diabetes. Experts recommend Ozempic for Type 2 diabetes treatment in certain people because it can lower body weight.

It's not clear how Ozempic affects people who aren't considered overweight or obese. For people with lower body weights, Ozempic levels in the body may be even higher. More research is needed to know for sure.

Can you switch from phentermine to Ozempic?

Yes, you can switch from phentermine to Ozempic. As mentioned, Ozempic is a Type 2 diabetes medication. But it's often prescribed off-label for weight loss in people who don't have diabetes. If you're not getting the results you want with phentermine, or if you need a long-term option, your prescriber may recommend Ozempic (or Wegovy).

Can you take Ozempic and phentermine together?

You may be able to take Ozempic and phentermine together. This hasn't been studied, so it's not clear if the combination is safe. We don't know if taking them together provides greater weight loss. There's a lack of research. As a result, phentermine has a warning about combining it with other weight-loss medications.

Even so, your prescriber may have you take Ozempic and phentermine together. Tell them if this combination results in any new or worsening side effects.

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