Can you take phentermine and semaglutide together?

Semaglutide and phentermine are prescription medications that can help with weight loss. Since both medications can support weight loss, you might wonder if you can take phentermine and semaglutide together to give your efforts an extra boost. 

The short answer is: maybe. Caution is advised, and there is only one case study — a study of a single person — exploring the safety and effectiveness of taking semaglutide and phentermine together. The prescribing label for phentermine also carries some warnings about taking it with other weight loss medications (such as Wegovy) or diabetes medications (such as Ozempic or Rybelsus). 

Ultimately, the best person to ask this question is your healthcare provider. You may or may not be a good fit for one or both drugs based on your personal medical history, current health conditions, and other medications you are taking. 

The main potential benefit of taking phentermine and semaglutide together is increased weight loss. In a case study of a 23-year-old man — currently the only research available on combining these two medications — taking both semaglutide with phentermine did lead to additional weight loss. 

However, there are some caveats to this study:

• A case study only observes a single person, and weight loss results often vary from person to person.

• The person in the study didn’t rely on phentermine and semaglutide alone. He took phentermine, topiramate, and metformin for a year, which caused a small amount of weight loss. Then he started taking semaglutide and following a lower-calorie diet.

• Given the mix of medications, it’s difficult to parse out whether the weight loss can be attributed to the combination of phentermine and semaglutide, just one of those medications, or the complete mix of medications and dietary changes. 

• His weight loss increased significantly once he started taking semaglutide, which may suggest the medication was primarily responsible — but it’s not possible to draw conclusions based on a single person.

For reference, phentermine can be prescribed separately as a short-term weight loss medication, but it’s also available in a combination medication with topiramate (Qsymia) for long-term use. Metformin is a diabetes medication that may be prescribed off-label for weight loss.  

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There are potential risks to taking semaglutide and phentermine together, since combining these medications for weight loss has not been studied in large-scale clinical trials. The phentermine drug label recommends against taking the medication alongside any other medication that can cause weight loss.

Side effects

Both semaglutide and phentermine cause side effects, some of which can be serious. Combining them may increase risks — including hypoglycemia in people with type 2 diabetes, which is specifically mentioned in the FDA drug label of phentermine. 

Both medications can cause side effects such as diarrhea, constipation, dizziness, and headache. Common side effects are listed below.

Serious side effects of semaglutide may include acute pancreatitis, kidney or gallbladder problems, an allergic reaction to the drug, pulmonary aspiration during surgery, or vision changes (in people with type 2 diabetes). Serious side effects may include primary pulmonary hypertension, regurgitant cardiac valvular disease, and abuse or dependence. 

Drug interactions

The prescribing label for phentermine specifically recommends against taking it with other weight loss medications, such as semaglutide or bupropion/naltrexone. Beyond that, here are the drug interactions to know about for both drugs:

• People taking insulin may need to adjust their insulin dosage when taking semaglutide or phentermine, as either drug may increase the risk of hypoglycemia (low blood sugar). 

• Phentermine should not be mixed with alcohol, monoamine oxidase inhibitors, or adrenergic neuron-blocking drugs.

• Because semaglutide slows digestion, it may affect the absorption of oral medications, including phentermine.  

Risk groups

Taking either semaglutide or phentermine can be risky for people with certain health conditions. For example, people with type 2 diabetes and kidney or gallbladder issues may need extra monitoring when taking semaglutide. Additionally, semaglutide should not be used by:

• Pregnant people

• People of any sex  planning to conceive in the near future

• Anyone with a personal or family history of certain thyroid cancers, including medullary thyroid carcinoma (MTC) and multiple endocrine neoplasia syndrome type 2 (MEN 2)

Phentermine should not be used by people who are pregnant or nursing, who have recently started taking monoamine oxidase inhibitors, or who have:

• A history of heart problems

• Hyperthyroidism

• Glaucoma

• Agitation

• A history of substance use disorder

In most cases, combining semaglutide and phentermine is not recommended — even though the two medications are not known to directly interact. Research on this combination is extremely limited, and given that gap, it’s advisable to avoid using phentermine alongside other weight loss medications.

That said, people who are contraindicated for either medication face even greater risk when taking them together. This includes anyone who:

• Is pregnant or breastfeeding

• Is trying to get pregnant (men and women included)

• Is taking monoamine oxidase inhibitors, adrenergic neuron-blocking drugs, or other GLP-1 medications

• Has a history of drug abuse or dependence

• Has high blood pressure, even if it’s mild

• Has poor kidney function

• Has a history of heart disease

• Has glaucoma

• Has hyperthyroidism

• Has a personal or family history of certain thyroid cancers

Semaglutide is the active ingredient in Ozempic, Wegovy, and Rybelsus. Ozempic and Wegovy are available as once-weekly injectable medications or daily pills, while Rybelsus is a daily oral medication. Each medication contains a different dose of semaglutide and is intended for long-term use alongside a balanced eating plan and exercise. 

Different forms of semaglutide are FDA-approved to treat different conditions. Ozempic and Rybelsus are both approved to treat type 2 diabetes by lowering blood sugar levels. Both are also approved to lower cardiovascular risk in people with both type 2 diabetes and heart disease. Ozempic is approved to slow kidney decline in people with type 2 diabetes and chronic kidney disease. 

Because they can lead to weight loss, healthcare providers may prescribe Ozempic or Rybelsus off-label for weight loss,  since neither is FDA-approved specifically for that purpose. 

Wegovy is the only medication containing semaglutide that is FDA-approved specifically for weight loss. It may be prescribed to adults with obesity or with overweight and a weight-related health condition such as high blood pressure or cholesterol. 

In one clinical trial, people taking the 2.4 mg dose of Wegovy lost nearly 10% of their body weight after 28 weeks. Within two years, people taking the 2.4 mg dose of semaglutide lose over 15% of their body weight, on average.

The most common side effects of semaglutide are gastrointestinal, including nausea, diarrhea, and vomiting. These side effects are most common in the beginning weeks of treatment and tend to subside as your body adjusts to the medication. 

Unlike semaglutide, phentermine is intended as a short-term medication, in part because people develop a tolerance to it. It is an FDA-approved appetite suppressant for people with obesity (BMI of 30 or higher) or overweight (BMI of 27 or higher) with a weight-related health condition, and should be used alongside a balanced eating plan and exercise.

Phentermine may be sold under the brand names Adipex-P, Lomaira, and Suprenza, or as Qsymia, which combines phentermine and topiramate.

While the FDA recommends limiting phentermine treatment to three months, some people have more success when they take phentermine for up to six months, especially if it didn’t work well during the first three months. For 42% of people who did not lose much weight within the three-month time period, it took up to six months to lose at least 5% of their body weight with phentermine. 

Whether taking phentermine for a longer period of time is safe or effective for you is a conversation to have with your healthcare provider. Overall, individual responses to the medication vary, which accounts for some of the differences seen across available studies.

Phentermine’s side effects vary but can include dry mouth, headache, sweating, and unpleasant taste. Side effects can be more common with higher doses of phentermine. 

Generally, semaglutide results in more weight loss than phentermine. On average, people taking Wegovy lose 15% of their body weight in 68 weeks. People lose 6% by three months, and nearly 11% by six months. Meanwhile, about half of people taking phentermine lose at least 5% within three months. By six months, roughly 80% have reached that 5% milestone. 

The better option depends on a number of factors, as results can vary widely based on your personal response to the medication, existing health conditions, adherence to a healthy eating plan and exercise routine, and tolerance for side effects.

Your decision may also depend on how much weight you have to lose. People taking semaglutide may lose anywhere between 9.6%–17.4% of their body weight within 68 weeks, while those taking Qsymia (phentermine/topiramate) may lose 5% to 10.6% within a year. People taking higher doses of either medication tend to lose more weight. 

Finally, cost may be a consideration. Phentermine is usually much cheaper than semaglutide since it’s available as a generic. Wegovy costs $149–$349 for a monthly supply without insurance on Ro. Phentermine, on the other hand, usually costs less than $20 for a month’s supply. 

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Phentermine and semaglutide are both effective medications for weight loss, so it’s natural to wonder if you can combine them for even better results. In general, this isn’t recommended due to the lack of research on both safety and effectiveness.

• The prescribing information for phentermine specifically recommends against taking it with other weight loss drugs, which may include semaglutide drugs like Wegovy.

• Caution should also be used when combining phentermine with diabetes medications, which can include semaglutide drugs like Ozempic or Rybelsus.

• Only a single case study has been conducted analyzing the potential benefits of taking semaglutide and phentermine together for weight loss.

• Given the lack of large-scale, placebo-controlled trials, the risks of combining phentermine and semaglutide outweigh the potential benefits.

• If you’re trying to decide between phentermine and semaglutide for weight loss, semaglutide has been shown to produce significantly more weight loss.