Naltrexone is one of the two active ingredients of weight loss drug “Contrave”. One Contrave tablet contains 8 mg of naltrexone hydrochloride. It is an opioid antagonist and FDA approved to treat alcohol and drug dependence. It treats obesity by reducing craving for food intake. However, naltrexone HCl is not your everyday pill for getting rid of a headache. You should be familiar with its effects before deciding if you want to buy Contrave diet pill.


The molecule was created in 1963 as an orally active opioid receptor antagonist. In 1984, naltrexone hydrochloride was approved by FDA to treat opioid addiction and alcohol addiction.

As per WHO (world health organization) publication in 1996, it is safe and effective in the treatment of alcohol dependence.

Clinical research and studies:

A lot of preclinical and clinical studies/randomized clinical trials were conducted on low dose naltrexone hydrochloride molecule alone and in combination with other molecules (e.g. bupropion in Contrave) to identify its potential therapeutic usage.

Low dose naltrexone (LDN) is a daily dose of naltrexone that is approx. 1/10th of addiction treatment dose. LDN with hydrochloride (HCl) is good for treatment of chronic diseases, chronic pain conditions, inflammatory diseases and chronic obesity.

Naltrexone has a high level of affinity for the µ opioid receptor which controls eating habits. In some research studies on animals, it is found that the drug restricts the dopamine when eating and also decreases food intake and craving for food. This way it reduces reduce food intake. Some human studies suggested that naltrexone decreases the liking of certain foods. Gender-based studies also reveal that weight loss is significant in females.

There is this research conducted by prof. Tek (2015), sponsored by Yale university. The study is conducted in parallel with a placebo group. The objective of the study was to find out the effects of naltrexone in reducing the body weight of human beings taking antipsychotic drugs as compared to the ones treated with placebo. Adult Patient with BMI 28 or more was taken to study. It is observed that schizophrenic patients get obese fast as compared to otherwise healthy individuals. Thus if Contrave is given to such patients, they show significant improvement in weight loss. It is always recommended to consult the physician before taking Contrave if the patient is on some antipsychotic treatment.

It is observed that naltrexone and bupropion in combination (Contrave) works in synergy, independently and having complementary effects, thus impacts food intake and treats obesity.

In two clinical trials with Contrave (Contrave obesity research COR I and COR II), it is observed that Contrave weight loss results are competitive with other weight loss drugs e.g. Orlistat, Topiramate. These researches were conducted on obese and overweight patients for 56 weeks, with a balanced diet and regular physical exercise. These subjects (including diabetic patients) reduced significant weight (around 8.2%) compared with placebo groups.

How naltrexone molecule in Contrave works to treat obesity:

If you are registered for an obesity treatment and taking Contrave, or thinking to go for it, knowing how it works is a good to have information. Here are the possible ways Contrave treats obesity:

  • Reduce appetite: Increasing dose of the drug suppresses hunger and thus reduces food intake. It may create taste dislike which may lead to low intake of food.
  • Reduce alcohol intake: alcohol consumption is one of the causes for weight gain. Since naltrexone hydrochloride reduces alcohol intake, indirectly it helps in weight loss in alcoholic person.
  • Decrease cravings: As per available research, it reduces craving for high-fat food, thus low intake of a high-fat meal helps in losing weight.
  • High energy level: naltrexone increases the energy level of the individual, thus it increases the activity level of a person which in turn speed up metabolism & improves digestion. If you are taking Contrave and feeling energetic, it helps in your weight loss goal.
  • Hormone changes: naltrexone administration alters the level of hormone, ghrelin, leptin, and thyroxine. Thus it reduces craving for sweets. Thyroid hormone improves metabolism and helps weight loss. It also impacts insulin secretion, & this way improves insulin sensitivity, improves metabolism and prevent excessive fat formation.
  • Mood Change: Sometimes people tend to overeat when in a bad mood. Naltrexone hydrochloride improves your mood, thus impact your dietary habits & food choices.

Every individual is different from other and it depends on many other factors such as person’s constitution, habits, health status (i.e. suffering from any disease or condition) for Contrave to work as expected.

Physiological actions and Pharmacokinetics:

After oral administration of Contrave in healthy individuals, approx. 96% of naltrexone hydrochloride gets absorbed. the peak concentration of the molecule and time to reach peak concentration is 1.4 ng/ml in three hours. After intravenous injection, systemic clearance is 3.5 l/min.

Excreted in urine: 53-79%


If you are taking/planning to take Contrave regimen to treat obesity, please take care of following points for a safe, effective and healthy weight loss with naltrexone hydrochloride:

  • You should always carry identification id when visiting a physician (even in the case of emergency), so that physician can be well aware of your Contrave weight loss plan.
  • Naltrexone hydrochloride increases sensitivity for opioids, so if you were on any opioid medication in past, there is a risk of opioid overdose. You should take a few days’ gap before starting Contrave & consult your doctor for the same.
  • If you are taking naltrexone hydrochloride, you may not get the opioid-containing analgesic, medicines.
  • You should notify the physician if you observe symptom related to liver disease while taking Contrave.
  • Dizziness may occur, so you should avoid driving or operate heavy machines until you well observe effects of the drug.
  • Notify physician if you are pregnant, breastfeeding or planning to become pregnant. (Pregnancy category C).
  • There is no proven effect of naltrexone hydrochloride on morphine, quinine, methadone detection in urine in a lab test.
  • Monitor vital signs and symptoms regularly during Contrave treatment.

Disclaimer: This article is for information only & should not be used as a resource for self- medication. Please consult your doctor before using the drug.