Contrave vs Phentermine: Differences and Similarities

Contrave vs Phentermine
Contrave and phentermine are prescription medications used to promote weight loss and weight management in patients who are obese or overweight. Phentermine is a controlled substance, while Contrave is not.

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According to the National Institutes of Health, an estimated 70.2 percent of adults in the United States are either overweight or obese.

Being overweight or obese puts patients at a higher risk of experiencing dangerous health conditions, including high blood pressure, high cholesterol, heart disease, and diabetes, all of which can contribute to premature death. 

Patients who want to lose body weight but struggle to do so through diet and exercise alone may turn to prescription drugs like Contrave and phentermine for assistance. 

When comparing Contrave vs. phentermine, there are a number of differences and similarities. 

Contrave vs. Phentermine: Overview

Both weight loss medications are Food and Drug Administration (FDA) approved through clinical trials.

Contrave is a brand-name prescription medication that is composed of two active ingredients: naltrexone and bupropion. 

Contrave can only be obtained with a prescription. Contrave contains a combination of naltrexone, an opioid antagonist, and bupropion, an aminoketone antidepressant.

The medication is available in the form of an extended-release oral tablet.

Phentermine is a generic drug that is sold under the brand name Adipex-P. It’s also available in combination as phentermine/topiramate under the brand name Qsymia. Phentermine is considered an anorectic and central nervous system stimulant.

Available by prescription only, phentermine is available as an oral tablet or oral capsule.

Contrave vs Phentermine
Contrave vs Phentermine

Phentermine is considered a Schedule IV controlled substance by the U.S. Drug Enforcement Administration (DEA), meaning it has a relatively low risk of abuse and dependence.

Contrave vs. Phentermine: Conditions Treated

Both Contrave and phentermine are weight loss drugs that are used to treat people who are obese or who are overweight with other risk factors, such as hypertension (high blood pressure), diabetes, and hyperlipidemia (high cholesterol). 

Whether a person is categorized as being obese or overweight depends on their body mass index (BMI), which is calculated by dividing a person’s weight in kilograms by their height in meters squared. A healthy BMI is considered to be between 18.5 to 24.9. 


Obesity is a medical condition that results from a multitude of factors and is generally defined as carrying a much larger amount of weight on the body than is considered ideal for optimal health. The Centers for Disease Control and Prevention (CDC) defines obesity based on a BMI of 30.0 or higher. There are three classes of obesity:

  • Class I is defined by a BMI of 30 to 34.9
  • Class II is defined by a BMI of 35 to 39.9
  • Class III is defined by a BMI of 40 or higher

People with Class III obesity are said to have “extreme” or “severe” obesity. It should be noted that while the BMI index is considered accurate for the majority of the population, people who have a higher than average muscle mass may be mistakenly categorized as overweight or obese based on the BMI scale. Therefore, it is important that patients consult with their doctors about their lifestyle. 

Obesity can have serious consequences on your health, as it is associated with many of the leading causes of death in the United States and worldwide, including diabetes, stroke, heart disease, and some types of cancer. People with obesity are also at risk of certain mental health problems

There are a number of different factors that contribute to obesity, including behavior and genetics, physical activity, dietary patterns, inactivity, and the use of certain medications.

Overweight with other risk factors

The CDC considers a BMI of 25.0 to 29.9 to be overweight. 

Being overweight alone is not considered enough of a health risk to justify treatment with prescription medications like Contrave and phentermine, so patients who fall into the overweight BMI category must also have other risk factors to be prescribed the medications. These risk factors include high blood pressure, diabetes, and high cholesterol, all of which have been shown to improve with weight loss

How They Work

Contrave and phentermine work differently to promote weight loss. 

The exact mechanism by which Contrave works is not completely understood, but it is believed that the medication affects two different parts of the brain involved with appetite.

‘The medication is believed to target the hypothalamus, which is the region of the brain that controls hunger, and the mesolimbic reward system, which helps to control cravings. These two parts of the brain can cause people to overeat.

Phentermine is an appetite suppressant that is believed to work by acting on the levels of neurotransmitters in the brain, including norepinephrine, dopamine, and serotonin.

Although the exact mechanism by which phentermine works is unknown, studies have shown that higher levels of norepinephrine, dopamine, and serotonin may correspond to lower levels of hunger. 

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Contrave vs. Phentermine: Side Effects

Both Contrave and phentermine are associated with a long list of possible side effects. Side effects associated with Contrave and phentermine are classified as common and serious. 

Common side effects of Contrave include:

  • Insomnia
  • Diarrhea
  • Dry mouth
  • Nausea
  • Constipation
  • Vomiting
  • Headache
  • Dizziness

Common side effects associated with phentermine include:

  • Nausea
  • Dizziness
  • Headache
  • Difficulty sleeping
  • Irritability
  • Nausea
  • Vomiting
  • Diarrhea
  • Dry mouth

Some side effects associated with Contrave can be serious. Serious side effects of Contrave include:

  • Increases in blood pressure or heart rate
  • Suicidal thoughts or actions
  • Seizures
  • Manic episodes
  • Visual problems (symptoms include eye pain, changes in vision, swelling or redness in or around the eye)
  • Liver damage or hepatitis
  • Low blood sugar (hypoglycemia) in people with type 2 diabetes who also take medicines to treat their diabetes
  • Severe allergic reactions

Serious side effects associated with phentermine include:

  • Fast or irregular heartbeat
  • Mental or mood changes
  • Uncontrolled muscle movements
  • Changes in libido
  • Severe headache
  • Trouble speaking
  • Seizure
  • Weakness on one side of the body
  • Vision changes

If side effects develop, continue, or worsen, seek medical advice from your healthcare provider.

Contrave vs. Phentermine: Use

Contrave and phentermine are used differently to help treat patients who are obese or overweight with risk factors.

Both drugs should be combined with an appropriate reduced-calorie diet or exercise routine and should not be used as a sole treatment for weight loss. 

Contrave is approved for long-term use in patients and is typically used for four weeks or more.

The medication is usually taken in the morning and evening. 

By contrast, phentermine acts directly on the central nervous system and has a stimulant effect.

Phentermine is approved only for short-term use of a few weeks, as the medication can be addictive, and it is usually taken once per day in the morning before breakfast. 

Contrave vs. Phentermine: Risks

Both Contrave and phentermine are associated with a number of risks. 

Contrave should not be taken by people who have comorbidities such as:

  • Have uncontrolled high blood pressure
  • Use other medications that contain bupropion
  • Are dependent on opioid pain medications or medications that help reduce opioid dependency
  • Are in opioid withdrawal
  • Drink alcohol excessively
  • Are pregnant or planning to become pregnant
  • Have or have had seizures
  • Have or have had an eating disorder

Additionally, Contrave may increase the risk of suicidal thinking, particularly in children, adolescents, and teens. Contrave should not be used by children under the age of 18. 

Phentermine should not be used by people who have heart disease or heart problems, hyperthyroidism, or glaucoma. Those who are pregnant or nursing should not take phentermine due to the risk of fetal harm. People taking MAOIs, a type of medication used to treat depression, also should not take phentermine. Phentermine should not be used by people under the age of 16.

Contrave vs. Phentermine: Cost

Contrave is a brand-name drug and no generic alternative is currently available. A monthly prescription of Contrave costs about $80 and may not be covered by all forms of commercial insurance, Medicare, or Medicaid. 

By contrast, phentermine is available from a number of different manufacturers and is available in both brand-name and generic forms. A one-month supply of generic phentermine may cost less than $15, although it’s important to check with your insurance plan or pharmacy.


Contrave and phentermine both offer effective treatments for obesity and being overweight with risk factors, and can help patients lose more weight than they would through diet and exercise alone. 

Contrave is not a controlled substance and is intended for long-term use, while phentermine is intended only for short-term use and is a controlled substance. 

Other drugs that may help with weight-loss include orlistat, which comes in the common brands Xenical and Alli. 

Consult with your doctor before starting any new drugs, whether they’re prescription or over-the-counter. Phentermine is considerably less expensive than Contrave, but patients can save on either medication with a pharmacy discount card from

References, Studies, and Sources:

We are committed to providing our readers with only trusted resources and science-based studies with regards to medication and health information. 

Disclaimer: This general information is not intended to diagnose any medical condition or to replace your healthcare professional. If you suspect medical problems or need medical help or advice, please talk with your healthcare professional.

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