Contrave vs. Phentermine for weight loss

Contrave vs. Phentermine: Which Treatment is Better for Weight Loss?

It all depends on why you’re struggling to lose weight.

30-Second Takeaway

  • Contrave supports weight loss by decreasing cravings and compulsive eating habits in people with binge eating disorder.
  • Phentermine is a short-term weight loss drug that reduces appetite and increases calorie burning.
  • To qualify for Contrave or phentermine, you must have a BMI of over 30 or a BMI of 27+ with at least one weight-related condition such as type 2 diabetes.


or some people, losing weight isn’t as simple as mustering the willpower to eat a balanced diet and exercise four to five days a week. Metabolic disorders, long-standing binge-eating habits, and other health conditions can make it seem impossible to shed stubborn pounds. That’s when weight loss medications like Ozempic, Contrave, or phentermine may aid in weight loss when combined with a diet and exercise routine. 

Four percent of adults trying to lose weight in the United States are opting for weight loss drugs—pills, peptides, injections, and more—to help them on their fitness journey, according to a 2023 poll by the Kaiser Family Foundation (1). 

While GLP-1 drugs like Ozempic seem to be getting all the attention, high demand and the price tag can make them inaccessible for many. Luckily, there are a handful of other options that your doctor may prescribe you to help with weight loss. 

Although there are just six FDA-approved weight loss medications—bupropion-naltrexone (Contrave), liraglutide (Saxenda), orlistat (Xenical and Alli), phentermine-topiramate (Qsymia), semaglutide (Ozempic and Wegovy), and setmelanotide (Imcivree)—it can be hard to decide which medication is best for you; as each one comes with it’s own benefits and risks. Two doctors explain the benefits and differences of Contrave vs. phentermine.

About the Experts:

Janese Laster, M.D., is board certified in Internal Medicine, Gastroenterology, Obesity Medicine, and Nutrition at Georgetown University Hospital. She is also the founder of Gut Theory Total Digestive Care, a weight loss clinic in Washington, D.C.

Steven Batash, M.D., is a board-certified gastroenterologist and leading physician at Batash Endoscopic Weight Loss. He specializes in medication-supported and non-surgical weight loss solutions.

Contrave vs. Phentermine

What is Contrave?

Contrave is a prescription weight loss pill that contains two active ingredients: Naltrexone and bupropion (2). According to Janese Laster, M.D., this medication is mostly prescribed to people who struggle with emotional eating or binge eating disorders.

Naltrexone is an opioid antagonist, which is an FDA-approved class of drugs used to treat opioid use disorder and alcohol use disorder. It binds to opioid receptors in the brain and prevents release of endorphins (the chemicals in your brain that make you feel good) (3). 

Naltrexone works to help individuals with addiction by preventing these pleasurable feelings associated with alcohol and opioid use. Overtime, drugs, alcohol and even food, can hijack the brain’s reward center creating an unhealthy addiction cycle. If you’re someone who experiences addiction, naltrexone can help prevent cravings and urges associated with addiction. 

Naltrexone can also help you lose weight, Laster, says. It’s the main ingredient in several off-label weight loss drugs because it effectively blocks food cravings, too (4, 5). 

People who take the medication say that naltrexone freed them from binge eating disorders, improving their mental health and making it easier to lose weight.

Bupropion—the active ingredient in common antidepressants like Wellbutrin and Aplenzin—helps restore the brain’s balance of dopamine and norepinephrine, neurotransmitters that are involved in reward, stress, and memory (6). A healthy balance of these two hormones can help stave off symptoms of depression and anxiety (7). 

When combined, bupropion and naltrexone may work together to not only reduce hunger cravings, but also reduce stress associated with food cravings and urges and improve mental awareness which all can have positive effects on weight loss. This could explain why Contrave is such an effective weight loss medication when used with diet and exercise. Some people who have taken the medication say that they were able to stick to a balanced diet for the first time after starting Contrave. Others with binge eating disorder say this medication finally quieted the “food noise,” or obsessive internal dialogue about eating.

To qualify for a Contrave, you must be overweight (a body mass index (BMI) of 27 or above) with weight-related conditions—like type 2 diabetes, high blood pressure, sleep apnea or high cholesterol or obese (BMI of 30 or above) (8).

What is Phentermine?

Phentermine is an extended-release capsule that is a sympathomimetic (stimulant) drug which increases heart rate and blood pressure. Amphetamines are also under the stimulant drug class. It is not exactly certain how phentermine helps with short-term weight loss but it is believed to decrease appetite. 

“Phentermine stimulates the nervous system to increase heart rate and blood pressure,” Steven Batash, M.D. explains. “The increased heart rate and blood pressure levels result in a feeling of fullness (9).” 

Some people report the medication’s stimulant effect also increases their energy levels, making it easier and more enjoyable to workout. 

Unlike Contrave, which is used long-term to reduce cravings in people with binge-eating disorder, phentermine is typically prescribed for short-term use, says Batash. 

Phentermine is available as a generic medication and as two name-brand drugs: Adipex-P and Lomaira. It is also combined with other drugs like topamax (topiramate, an anti-epileptic) but can be used off-label for weight loss (10).

To qualify for a phentermine, you must be overweight (a body mass index (BMI) of 27 or above) or obese (BMI of 30 or above) (11). If your BMI is below 30, you’ll also need to have a weight-related condition—like type 2 diabetes, high blood pressure, sleep apnea, or high cholesterol—to get a prescription.

How Effective is Contrave for Weight Loss?

Across three placebo-controlled clinical trials, adults who took Contrave for weight loss achieved two to four times more weight loss than with a balanced diet and exercise alone over the course of a year (12). 

In one study, the Contrave group lost an average of 5.4 percent of their body weight compared to the placebo group, who lost 1.3 percent (12). Additionally, 42 percent of Contrave patients lost more than 10 percent of their body weight. While it’s unknown if stopping medication causes weight gain (13), some people who quit Contrave say that their compulsion to overeat came back, halting their weight loss progress. 

After starting Contrave, you can expect to lose 5 percent of your body weight when paired with diet and regular exercise after 12 weeks of treatment (1). For people struggling with obesity, research shows that losing 5-10 percent of your body weight can significantly improve quality of life and reduce the risk of conditions like type 2 diabetes and sleep apnea (14). 

If you don’t experience this level of weight loss, your doctor may stop or adjust your treatment (1). 

Risks of Contrave

Common side effects of Contrave might include dry mouth, headache, gastrointestinal issues like constipation, and dizziness (15).

However in some rare cases, Contrave can cause more serious side effects such as seizures, skin irritations, and allergic reactions (15). Those types of symptoms warrant a call to your doctor immediately.

You shouldn’t take Contrave with other drugs that contain bupropion—such as Wellbutrin, Wellbutrin SR, Wellbutrin XL, Aplenzin, and Zyban—since too much bupropion may cause side effects like vomiting, seizures, and hallucinations (16). 

If you’re experiencing a mental health emergency, contact the Suicide and Crisis Lifeline at 988. 

How Effective is Phentermine for Weight Loss?

A 2010 study in the journal Diabetes, Obesity, and Metabolism found that 96 percent of adults with obesity who took phentermine for 12-weeks lost at least 5 percent of their body weight (17). Within that same group, 62 percent lost more than 10 percent body weight. This dramatic weight loss significantly improved peoples’ total cholesterol and low-density lipoprotein cholesterol (frequently called “bad cholesterol”) levels.

Phentermine is only approved in the United States for short-term weight loss treatment in combination with a diet and exercise regimen. This is because phentermine has a high dependence and addiction profile since it is a stimulant medication and can have similar addictive effects as amphetamines. 

However, long-term studies are investigative if it can be effective—and safe—for long term use. For example, a 2021 study found 80 percent of adults who took phentermine for six-months lost at least 5 percent of their body weight (18). Up to 20 percent of people who took phentermine regained some of their body weight back after stopping treatment.

Risks of Phentermine

Common side effects of phentermine include (19):

  • Dry mouth, often with an unpleasant taste
  • Gastrointestinal issues like constipation and diarrhea
  • Vomiting


Because phentermine increases heart rate and blood pressure, you shouldn’t take it if you have a pre-existing heart condition (20). For obese people with heart conditions, Contrave will likely be prescribed over phentermine, according to Batash. 

Phentermine is considered a controlled-substance, because it has a risk of abuse and dependency (21). People who have previously struggled with substance abuse disorder said that they were put-off by the stimulant effects of this medication. If you are in recovery, talk to your doctor about how phentermine could impact your progress. 

If you experience any of the following serious phentermine side effects, contact your doctor ASAP (19):

  • Insomnia
  • Heart palpitations
  • High blood pressure
  • Chest pain
  • Tremors and restlessness
  • Shortness of breath
  • Abdominal pain

Contrave vs. Phentermine: Which is More Effective for Weight Loss?

If you have a binge eating disorder, your doctor may prescribe Contrave, as it can soften the rewarding feeling associated with overeating—especially when you’re stressed out or craving your favorite snack. 

Phentermine is more frequently prescribed to people with conditions like insulin resistance, which can make it difficult to lose weight even when sticking to a balanced diet and workout regime (22). 

If you’re curious about using weight loss medication on your health journey, talk to your doctor about what treatment is right for you.

1. Montero, et al (2023). KFF Health Tracking Poll July 2023: The Public’s Views Of New Prescription Weight Loss Drugs And Prescription Drug Costs.
2. Sherman, et al (2016). Naltrexone/Bupropion ER (Contrave).
3. Theriot, et al (2023). Opioid Antagonists.
4. REVIA® Consumer Medicine Information.
5. FDA. Vivitrol.
6. Huecker, et al (2023). Bupropion.
7. Nutt (2006). The role of dopamine and norepinephrine in depression and antidepressant treatment.
8. Checklist for a Prior Authorization (PA) for CONTRAVE®
9. Jordan, et al (2014). Cardiovascular effects of phentermine and topiramate: a new drug combination for the treatment of obesity.
10. Lonneman, et al (2013). Phentermine/Topiramate Extended-Release Capsules (Qsymia) for Weight Loss
11. Phentermine Prescribing Information
12. What is CONTRAVE?
13. Early, et al (2015). Naltrexone/Bupropion (Contrave) for Weight Loss.
14. Roux, et al (2022). The relationship between early weight loss and weight loss maintenance with naltrexone-bupropion therapy.
15. Contrave®8/90 Customer Medicine Information
16. Shepherd (2005). Adverse effects associated with extra doses of bupropion.
17. Kang, et al (2010). Randomized controlled trial to investigate the effects of a newly developed formulation of phentermine diffuse-controlled release for obesity.
18. Marquez-Cruz, et al (2021). Three- and six-month efficacy and safety of phentermine in a Mexican obese population.
19. MedlinePlus. Phentermine.
20. Manasrah, et al (2022). Phentermine-Associated Atrial Fibrillation: A Case Report and Literature Review.
21. Why is phentermine a controlled substance?
22. Garvey, et al (2014). Prevention of Type 2 Diabetes in Subjects With Prediabetes and Metabolic Syndrome Treated With Phentermine and Topiramate Extended Release