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Contrave vs. phentermine: Differences, similarities, and which is better for you

Contrave and phentermine are two medications prescribed for weight loss

What’s the difference? | Conditions treated | Insurance & costs | Efficacy | Dosage | Side effects | Drug interactions | Warnings | FAQ

Nearly three-quarters (73.6%) of adults 20 years and older are overweight (including obesity), and the percentage of adults with obesity is 42%, according to the Centers for Disease Control and Prevention (CDC). Obesity can cause a number of complications, such as Type 2 diabetes, high cholesterol, metabolic syndrome, high blood pressure, heart attack, stroke, and sleep apnea. 

Healthcare professionals recommend a variety of methods to lose weight, most commonly changing eating habits and exercising. In some cases, they also recommend prescription weight-loss medication, counseling, or surgery.

Contrave and phentermine are two medications for weight loss. Both are prescription weight-loss drugs approved by the United States Food and Drug Administration (FDA). Although both drugs are prescribed for weight reduction, they have many differences. This article will provide detailed information about both weight-loss medicines. 

RELATED: More FDA-approved weight-loss pills

Contrave vs. phentermine: What’s the difference?

Contrave Phentermine
Drug class Naltrexone: opioid antagonist

Bupropion: antidepressant

Brand/generic status Brand Brand and generic
What is the generic/brand name? The chemical name is naltrexone-bupropion, but there is no generic available Brand names are Adipex, Adipex-P, Atti-Plex, Fastin, Ionamin, and Lomaira (not all are available in brand name). Also, Qsymia is a drug that contains phentermine in combination with topiramate.
What form(s) does the drug come in? Extended-release tablet Capsules, tablet
What is the standard dosage? The dosage is increased weekly over 4 weeks to 2 tablets by mouth twice a day, in the morning and evening (but not with a high-fat meal). The tablet should not be cut, chewed, or crushed. 15 to 37.5 mg by mouth every morning. The tablet may be split but not cut, crushed, or chewed. 
How long is the typical treatment? Long-term but exact amount of time varies. In clinical studies, participants took Contrave for up to 56 weeks. Short-term: should be tapered when tolerance occurs, usually within a few weeks.
Who typically uses the medication? Adults with a BMI of 30 kg/m2 or more (obese) or 27 kg/m2 or more (overweight) with at least one other weight-related risk factor. Adults with a BMI of 30 kg/m2 or more—or 27 kg/m2 or more with at least one other weight-related risk factor/comorbidity.
More information What is Contrave? What is phentermine?

What is Contrave?

Contrave is a prescription weight-loss medicine that is available as a brand name only. You cannot buy Contrave over the counter. The way Contrave works for weight loss is not entirely understood. It is thought that the two ingredients in Contrave work on two separate areas of the brain that regulate food intake. Contrave should be used along with a reduced-calorie diet and increased physical activity.

Contrave is a combination of naltrexone and bupropion. Naltrexone is an opioid antagonist and bupropion is an antidepressant. 

Unlike phentermine, Contrave is not a controlled substance. 

RELATED: Antidepressant weight gain statistics

What is phentermine?

Phentermine is a generic prescription drug used for weight loss. You cannot buy phentermine over the counter. Phentermine brand names include Adipex, Adipex-P, Atti-Plex, Fastin, Ionamin, and Lomaira. Phentermine is classified as an anorectic drug. It is a stimulant and acts similar to amphetamine. Phentermine is thought to work by various mechanisms, including actions on the central nervous system (CNS), metabolic effects, and possibly as an appetite suppressant. Like Contrave, phentermine should be employed along with diet and exercise.

Phentermine is a Schedule IV controlled substance, which means it has some potential for abuse and dependence.

What are Contrave and phentermine used for?

Contrave is indicated for chronic weight management in adults with a body mass index (BMI) of 30 kg/m2 or more (obese)—or 27 kg/m2 or more (overweight) with at least one other weight-related risk factor, such as high blood pressure, Type 2 diabetes, or high cholesterol. It should be taken in addition to diet and exercise to achieve the best Contrave weight loss results.

Although Contrave contains bupropion, which is the ingredient in the antidepressant Wellbutrin and is also used for smoking cessation, Contrave is not indicated for depression or smoking cessation

Phentermine is indicated as a short-term (several weeks) weight loss treatment. Adult patients with a BMI of 30 kg/m2 or more—or 27 kg/m2 or more with at least one other weight-related risk factor/comorbidity may be a candidate for a phentermine prescription. Like Contrave, phentermine should be taken along with diet and exercise.

RELATED: Best diet for weight loss

Insurance coverage and cost comparison

Contrave is sometimes covered by insurance plans but is generally not covered by Medicare prescription plans. A typical prescription for Contrave without insurance coverage should be no more than $199 if you pay out-of-pocket with a Contrave savings card from the manufacturer. A free coupon from SingleCare can also lower the Contrave price up to 80% off the original price. 

RELATED: Get the SingleCare prescription discount card

Generic phentermine is cheaper than brand-name Contrave. Although generic naltrexone and generic bupropion are available, generic Contrave, which contains both naltrexone and bupropion, is not yet available. Neither naltrexone nor bupropion should be used alone as a Contrave generic. A generic for Contrave may not be available until sometime in 2030. 

Insurance and Medicare prescription plans do not usually cover phentermine. Phentermine without insurance costs about $40 for 30, 37.5 mg tablets. However, a free SingleCare coupon can lower the price to less than $6.

Because insurance plans vary and can change, it is best to contact your insurance provider for up-to-date coverage information. 

Which is better: Contrave or phentermine?

There are no studies directly comparing phentermine vs. Contrave. Drug selection is based on a variety of factors, such as other medical conditions, anticipated side effects and drug interactions, and insurance coverage. For example, a patient who does not have insurance coverage may be better suited for phentermine, which is relatively inexpensive. On the other hand, Contrave may be a better choice in a patient with a history of substance use disorder. Either way, diet, and exercise are important to help with weight loss in addition to medication. 

Your healthcare professional can determine which, if any, drug is appropriate for you, taking into account your medical conditions, history, and drugs you take that could interact with Contrave or phentermine. 

Contrave reviews

In studies, over 56 weeks, the average weight loss in people taking Contrave was about 17 pounds. In these clinical trials, 42% of patients lost 5% or more of their body weight, 21% of patients lost 10% or more, and 10% of patients lost 15% or more.

According to a 2010 Contrave weight loss review published in Obesity, 1.5 times as many people taking Contrave with behavior therapy lost at least 5% of their body weight compared to people taking a placebo with behavior therapy.

Phentermine reviews

Phentermine results showed that almost half (45.6%) of 700 people with BMIs higher than 25 were able to lose 5% or more of their body weight after 12 weeks of using phentermine, according to a study published in the Korean Journal of Family Medicine


Contrave is indicated for long-term use while phentermine is indicated for short-term use. Phentermine often results in tolerance after several weeks, at which point it should be stopped.


If you are prescribed Contrave or phentermine, it is important to take the medication exactly as directed. To minimize the risk of overdose, do not take more medication than your healthcare professional prescribes. 

With Contrave, an overdose can cause seizures, hallucinations, loss of consciousness, heart problems, fever, muscle rigidity, muscle breakdown, low blood pressure, respiratory failure, and coma. It can possibly cause death when large doses are taken. 

An acute overdose of phentermine may cause excess stimulation of the central nervous system—leading to restlessness, tremor, rapid breathing, confusion, hallucinations, panic, and aggression, followed by tiredness and depression. Other overdose symptoms can include irregular heartbeat, changes in blood pressure, and stomach problems. 

Taking too much phentermine over time can lead to chronic intoxication, which can cause trouble sleeping, irritability, personality changes, hyperactivity, psychosis (similar to schizophrenia), and severe skin problems.

How to take Contrave for best results

Contrave is available as an extended-release tablet. Because the medication releases over time, the tablet should be swallowed whole and not cut, chewed, or crushed. 

The Contrave dosage is slowly increased, from one tablet in the morning, over a period of four weeks to its maintenance dosage of two tablets twice daily. Contrave should be taken in the morning and evening, but not with a high-fat meal. After 12 weeks at this maintenance dosage, if the patient has not lost at least 5% of body weight, Contrave should be discontinued. 

How to take phentermine for best results

Phentermine should be taken in the morning as directed by your doctor. It should be taken either before breakfast, or one to two hours after breakfast, to help control appetite. Your doctor will prescribe the lowest possible dose that is effective. Some patients will be prescribed a smaller dose several times daily. Taking phentermine at night should always be avoided, because the medication can cause insomnia. Phentermine is usually taken for a few weeks until tolerance develops. At that point, the drug should be discontinued.

Side effects

Contrave and phentermine have some similar side effects, such as stomach problems, headache, and difficulty sleeping. Serious side effects such as suicidal thoughts (Contrave) and heart problems (phentermine) may occur.

Common side effects of Contrave vs. phentermine

Contrave side effects Phentermine side effects
Shared common side effects
  • Constipation
  • Diarrhea
  • Dry mouth
  • Headache
  • Dizziness
  • Insomnia
Drug-specific side effects
  • Nausea
  • Vomiting
  • Heart problems: palpitations (feeling like the heart is racing or pounding), tachycardia (fast heart rate), high blood pressure
  • Mood changes like euphoria (feeling intensely happy) or dysphoria (feeling unwell)
  • Sexual changes such as impotence or loss of interest in sex
  • Restlessness
  • Tremor 
  • Unpleasant taste in the mouth 
  • Hives 

Report side effects or any changes that concern you to your doctor. Allergic reactions are rare, but if you experience symptoms of an allergic reaction such as hives, difficulty breathing, or swelling around the face, lips, tongue, or throat, get emergency medical help right away. 

This is not a full list of possible side effects, and other adverse effects may occur. Consult your healthcare professional for a full list of side effects. 

Drug interactions

Before taking Contrave or phentermine, tell your doctor about any allergies to medication, and all of the medications you take, including prescription drugs, over-the-counter medicines, and vitamins or supplements. Your doctor will need this information to determine if Contrave or phentermine is compatible with the other medications you take. 

Contrave vs. phentermine drug interactions

Contrave interactions Phentermine interactions
Interactions with both weight-loss drugs
  • Monoamine oxidase inhibitors (MAOIs)
  • Antidiabetic agents (insulin and oral diabetes medications)
  • Alcohol
  • Caffeine
Drug-specific interactions
  • Opioids
  • Drugs metabolized by an enzyme called CYP2D6 (antipsychotics, beta blockers, SSRI antidepressants, tricyclic antidepressants, Type 1C antiarrhythmics)
  • Digoxin
  • Drugs metabolized by an enzyme called CYP2B6
  • Drugs that increase dopamine
  • Tramadol
  • Beta blockers

This is not a full list of drug interactions. Consult your healthcare provider for a full list of drug interactions. 

RELATED: Phentermine and caffeine

Warnings of Contrave and phentermine

Before taking weight-loss meds, talk to your doctor about all of the medical conditions you have, and all of the medications you take, so your doctor can determine if weight-loss medications are safe for you. 

  • Do not take Contrave or phentermine with other weight-loss drugs, including prescription drugs, over-the-counter weight-loss pills, vitamins, or supplements.
  • With either drug, weight loss can result in low blood sugar. Blood glucose levels should be monitored. Report low blood sugar to your healthcare provider.
  • Contrave and phentermine can raise blood pressure. Blood pressure should be monitored.
  • Do not drive or operate machinery until you know how Contrave or phentermine affects you.
  • Do not drink alcohol with Contrave or phentermine.

Contrave vs. phentermine contraindications

Drug Contraindications
Contraindications for both weight-loss drugs
  • People with uncontrolled high blood pressure
  • Those who take MAOIs (or within 14 days of taking MAOIs)
  • Weight loss can cause harm to an unborn baby. Stop taking weight-loss drugs if you find out you are pregnant and contact your healthcare provider right away.
  • People who are allergic to any of the drug’s ingredients
  • People with seizure disorders
  • People with anorexia or bulimia
  • People who are abruptly stopping alcohol, benzodiazepines, barbiturates, or anticonvulsants
  • Those who take bupropion or opioids
  • People with a history of heart disease, including coronary artery disease, stroke, arrhythmia, or heart failure
  • People with hyperthyroidism, glaucoma, history of drug abuse, agitated states
  • People who are allergic to drugs in the class called sympathomimetic amines
  • People who are breastfeeding

Additional Contrave warnings

  • Contrave has a black box warning. This is the strongest warning required by the FDA. The warning states that although Contrave contains bupropion, an antidepressant, Contrave is not approved to treat depression or other psychiatric disorders. Antidepressants may cause an increased risk of suicidal thoughts and behavior in children, adolescents, and young adults up to age 24. Patients of any age who take Contrave should be closely monitored for suicidal thoughts and behaviors. Caregivers and families should observe the patient as well. Changes in mood/behavior, anxiety, agitation, or suicidal thoughts or behaviors should be immediately reported to the healthcare provider. Contrave is not approved for use in children younger than 18 years old. Contrave should not be taken with any other medications that contain bupropion. 
  • People taking Contrave for weight loss should be monitored for the development of psychiatric side effects including depression, mania, psychosis, hallucinations, paranoia, delusions, homicidal ideation, hostility, aggression, anxiety, panic, and agitation—in addition to suicidal thoughts and behaviors mentioned above. If symptoms occur, stop Contrave and contact your healthcare provider. Report sudden changes in mood or behavior to your doctor right away.
  • Contrave should be taken at the times prescribed. Contrave should not be taken with a high-fat meal. Taking the medication properly lowers the risk of seizures. If you have a seizure while taking Contrave, the medicine should be stopped and not taken again. 
  • Seizure risk is also increased with excess use of alcohol or with abruptly stopping alcohol, benzodiazepines, anticonvulsant drugs, or sedatives. Do not use alcohol while taking Contrave. 
  • If you have taken opioids in the past, you may be more sensitive to lower doses of opioids and there is a risk of accidental overdose if you take opioids again. This is due to the naltrexone ingredient in Contrave. Taking large doses of opioids can cause serious injury, coma, or death. Opioids should be discontinued at least 7 to 10 days before you start taking Contrave. Notify your doctor of any medications you take and any changes in medicine. 
  • Contrave may increase heart rate. Heart rate should be monitored, especially in patients with heart or blood vessel problems.
  • Contrave can cause liver problems. Tell your doctor if you have extreme tiredness, stomach pain, dark urine, or yellowing of the skin or whites of the eyes.
  • Contrave can cause angle-closure glaucoma. Ask your doctor if you are at risk. Call your doctor right away if you have eye pain or swelling, or vision changes. 
  • Swallow Contrave tablets whole—the medication is released over an extended time. Do not crush, chew, or divide Contrave pills.
  • If you need to take a urine drug test, tell the person giving the test that you take Contrave, as it can make the test show a positive result for amphetamines. 

Additional Phentermine warnings

  • Phentermine can cause pulmonary hypertension. If you have shortness of breath, chest pain, fainting, or swelling in the ankles and feet, stop taking phentermine and get medical attention. 
  • In rare cases, serious regurgitant cardiac valvular disease has occurred.
  • Take phentermine as prescribed, and do not take more than your doctor prescribes. Tolerance may occur in several weeks. If tolerance occurs, phentermine should be stopped.
  • Because phentermine is a controlled substance, there is a risk of abuse and dependence.

RELATED: Is phentermine for weight loss safe?

Frequently asked questions about Contrave vs. phentermine

Are Contrave and phentermine the same?

Contrave and phentermine are not the same. Contrave contains two ingredients: naltrexone and bupropion, and is used for long-term weight management. 

On the other hand, phentermine is a single-ingredient drug that is used for short-term weight loss. 

Either drug should be used along with other measures such as diet and exercise, per medical advice from your healthcare provider.

Does Contrave contain phentermine?

No. Contrave does not contain phentermine. Contrave contains naltrexone (an opioid antagonist) and bupropion (an antidepressant).

Can you take phentermine with Contrave?

Do not take a combination of phentermine and Contrave. It’s best to discuss options with your healthcare provider to determine which weight-loss drug is more appropriate for you.

What can you take instead of Contrave or phentermine?

Other common weight-loss drugs include Alli (orlistat), Xenical (orlistat), and Qsymia (phentermine/topiramate). Injectable drugs, which are used for Type 2 diabetes and/or weight loss, include Ozempic (semaglutide), Saxenda (liraglutide), Victoza (liraglutide), and new drug Wegovy (semaglutide). Ask your doctor about Contrave and phentermine alternatives.

RELATED: Topamax for weight loss: Safety and efficacy

How much weight will you lose on Contrave or phentermine?

While everyone may have a different experience, we can look at average weight losses with both drugs. Also, weight loss can also depend on other factors like dietary changes and exercise. 

In clinical trials for Contrave, between 36% and 57% of people (depending on which study) lost 5% or more of body weight, and 15% to 35% of people lost 10% or more. When healthcare professionals prescribe Contrave, if weight loss of 5% or more is not achieved by 12 weeks, the drug should be discontinued.

While phentermine is approved by the FDA for short-term use, many healthcare providers will prescribe it off-label for longer periods of time (or intermittently, with some time on and some time off). A meta-analysis of studies ranging from two weeks to 24 weeks found that people who took phentermine lost an additional 7.9 pounds more than those in the placebo group, with a mean total weight loss of 13.9 pounds.

Again, everyone has different results, so it is important to talk with your healthcare provider to find the best weight loss medication for you.

How quickly do Contrave and phentermine work?

People who participated in Contrave clinical trials started to lose weight at the 4-week mark.

Phentermine starts to work quickly to suppress hunger. You may start to notice a change in weight after a few weeks. 

Remember that with either drug, your doctor will recommend dietary changes and exercise, so it is important to follow your doctor’s recommendations to get the maximum benefit from your medication. 

Do you gain weight back after stopping Contrave or phentermine?

In clinical studies, patients lost the most weight after taking Contrave for 36 weeks and maintained weight loss through 56 weeks.

In terms of phentermine weight loss, studies were only done for a short period of time. Once you stop phentermine, your appetite will return to normal. As a result, weight gain may occur. However, continuing lifestyle changes like diet and exercise may help maintain weight loss.

Can I use Contrave or phentermine while pregnant?

Because weight loss can cause harm to an unborn baby, Contrave or phentermine should be stopped when a pregnancy is detected. Contact your doctor if you are pregnant or think you may be pregnant. You can find more information on Contrave and pregnancy here, and more information on phentermine and pregnancy here.

Can I use Contrave or phentermine with alcohol?

You should not mix Contrave or phentermine with alcohol. Taking Contrave with alcohol can increase the risk of psychiatric events. Excess use of alcohol or stopping alcohol abruptly can also increase the risk of seizures if you are taking Contrave. Phentermine mixed with alcohol increases the risk of adverse reactions.