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Opioid Antagonists for Weight Loss

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Opioid antagonists are drugs that have been used to treat alcohol, smoking, and opioid dependency. But researchers are also looking into their possible role in obesity treatment.1-3

How do opioid antagonists work?

Opioid antagonists work by blocking opioid receptors in the body’s central nervous system. The central nervous system includes the brain and spinal cord. Opioid receptors play a role in regulating appetite and body weight.1-3

By blocking these receptors, opioid antagonists affect reward pathways. This may reduce food cravings and decreases the motivation to eat, which can lead to reduced food intake and weight loss.1-3

The exact mechanisms of action and effectiveness of opioid antagonists in promoting weight loss are not fully understood. Research is underway to learn more.1

Example of an opioid antagonist used in weight loss

The US Food and Drug Administration (FDA) has approved the combination of naltrexone and bupropion (Contrave®) for use in obesity treatment. Naltrexone is an opioid antagonist. Contrave is an antidepressant and smoking cessation aid that may help reduce appetite and cravings.1,2,4-6

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Contrave is approved for use in adults who have a body mass index (BMI) of:6

  • 30 or greater
  • 27 or greater, with at least 1 weight-related condition such as high blood pressure, type 2 diabetes, or dyslipidemia

Contrave should be taken alongside a reduced calorie diet, regular exercise, and behavior changes. Clinical studies have shown that people taking Contrave, in combination with lifestyle changes, saw 4 to 5 percent more weight loss than those not taking it.1,2,4-6

Contrave is an extended-release tablet taken by mouth. Your doctor will advise you on the dosage that is right for you.5,6

For more information, read the full prescribing information of Contrave.

What are the possible side effects?

Side effects can vary depending on the specific drug you are taking. The most common side effects of opioid antagonists are:3,5,6

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

Contrave has a boxed warning, the strictest warning from the FDA. It has this warning because Contrave can lead to suicidal thoughts and behaviors in children, adolescents, and young adults taking antidepressants for depression and other mental health conditions. Contrave is not approved for use in children under age 18.5,6

These are not all the possible side effects of opioid antagonists. Talk to your doctor about what to expect when taking opioid antagonists. You also should call your doctor if you have any changes that concern you when taking an opioid antagonist.5,6

Other things to know

Obesity is a complex condition influenced by multiple factors. Treatment approaches should include lifestyle changes, diet, exercise, and behavior modifications.

Contrave is not right for everyone. It should not be taken by those who have:2,5,6

  • Uncontrolled high blood pressure
  • Seizure disorders
  • Eating disorders
  • A history of opioid or alcohol dependence

Do not take opioid antagonists if you are pregnant or intend to become pregnant. They could pose risks for the baby.5,6

While taking Contrave, regular monitoring by a healthcare professional is needed. They can assess how the drug is working, help manage side effects, and monitor any changes in blood pressure, mood, or other health issues.5,6

Before beginning treatment for obesity, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.

Talk with your doctor

Opioid antagonists should be used for weight loss only under the guidance and prescription of a healthcare professional. Talk with your doctor about whether opioid antagonists are right for you.