Naltrexone is one of the two active ingredients in Contrave, an FDA-approved weight-loss medication. It’s also taken off-label by some patients who notice their weight drops as they reduce drinking. The connection is real but partial: naltrexone helps with weight loss in two specific ways, and neither makes it a weight-loss drug on its own. This article is part of our Naltrexone hub, the complete guide to using naltrexone for alcohol use disorder.
This article walks through the actual mechanisms linking naltrexone to weight, what Contrave is and how it works, and how alcohol reduction itself drives weight loss for patients on naltrexone for alcohol use disorder.
# The two mechanisms
Naltrexone affects body weight through two distinct pathways:
Mechanism 1: Reducing alcohol intake. This is the indirect mechanism, and for patients taking naltrexone for alcohol use disorder, it’s the bigger effect. Alcohol contributes a substantial number of calories that most people don’t account for. We cover this in detail in our Alcohol Calories hub. Cutting drinking by 30-50% over months reduces total caloric intake meaningfully without any direct effect on metabolism.
Mechanism 2: Reducing food reward and craving. This is the direct mechanism. Naltrexone blocks mu-opioid receptors, which are involved in the reward signalling not just for alcohol but for highly palatable food (sugar, fat, salt combinations). Studies have shown naltrexone can modestly reduce food cravings, particularly for sweet and high-calorie foods, in patients who have those craving patterns.
Mechanism 1 is large and reliable. Mechanism 2 is small and variable.
# How alcohol calories add up
A few quick numbers to ground the first mechanism:
- A pint of standard beer (5% ABV): around 200 calories
- A 175ml glass of wine: around 150 calories
- A shot of spirits: around 65 calories before mixers
- A typical cocktail: 150-300 calories
- A single can of hard seltzer: around 100 calories
If you drink 4 pints of beer a night three times a week, that’s 2,400 alcohol calories per week. Cutting it to 2 pints per session drops you to 1,200 calories per week, a reduction of 1,200 calories. Over a year, that’s roughly 62,000 calories, which translates to about 8 kg (18 lbs) of body fat in expected weight loss, all else being equal.
This is the real mechanism behind most “I lost weight on naltrexone” stories. The drinking reduction is doing the work; naltrexone is the tool that made the drinking reduction possible.
We cover the math in more detail in Can You Lose Weight and Still Drink Alcohol? over in the Alcohol Calories hub.
# What Contrave is
Contrave is a combination drug containing 32mg of naltrexone (sustained-release) plus 360mg of bupropion (an antidepressant also used for smoking cessation). Approved by the FDA in 2014 for chronic weight management in adults with obesity (BMI 30+) or overweight (BMI 27+) with at least one weight-related condition.
The reasoning behind the combination: naltrexone alone has a small effect on food cravings; bupropion alone has a small effect on appetite suppression and energy. Together, they target the brain’s appetite/reward circuits more effectively than either alone, particularly the hypothalamic POMC system involved in satiety.
Clinical trials show Contrave produces about 5-10% body weight loss over 12 months for compliant patients, modestly better than placebo plus diet/exercise. Side effects include nausea (common, often persistent), constipation, headache, dizziness, and increased blood pressure or heart rate (which is why it’s contraindicated in patients with uncontrolled hypertension).
Contrave is more expensive than either of its components alone. In the US it’s around $200-400/month without insurance.
For patients on naltrexone for alcohol use disorder, Contrave is not usually the right choice; you’re already getting the naltrexone effect, plus the bupropion adds its own side-effect profile.
# Off-label naltrexone for weight loss
Some patients use plain naltrexone (50mg or low-dose 1.5-4.5mg) off-label for weight loss without bupropion. The evidence for this is weaker than for Contrave; the trials that established naltrexone-bupropion combination’s effect were specifically on the combination, not naltrexone alone.
For patients on naltrexone for alcohol use disorder who happen to also lose weight, the weight loss is mostly attributable to alcohol reduction (mechanism 1) rather than direct food-reward suppression (mechanism 2). Trying to use naltrexone purely for weight loss while drinking unchanged isn’t well-supported by the evidence.
Low-dose naltrexone (LDN) for weight loss is occasionally promoted in integrative medicine circles, but the evidence is even weaker than for full-dose. We cover LDN for alcohol and the same skepticism applies for weight applications.
# What patients actually report
In patient communities for alcohol use disorder using naltrexone, weight changes are common but variable:
- Some patients lose weight steadily over the first 6-12 months, primarily via alcohol-calorie reduction
- Some patients see no weight change, often because they’ve replaced alcohol calories with food (sober snacking, comfort eating, sugary substitutes)
- A minority gain weight, usually because the substitution toward food is more calorically dense than the alcohol it replaced
The patients who consistently lose weight tend to have done two things: significantly reduced their drinking AND not aggressively replaced the calories with food. The naltrexone is the tool for the first part; the second part is a separate behavioural decision.
# What you can realistically expect
For someone starting naltrexone for moderate-to-heavy drinking (e.g. 20+ drinks a week) with no other dietary changes:
- Months 1-3: Weight likely unchanged or slightly up (water retention, comfort eating during the side-effects window)
- Months 3-6: Weight starts to drop as drinks-per-session reduce and total caloric intake from alcohol falls
- Months 6-12: 3-7 kg (7-15 lbs) loss is typical for compliant patients who don’t aggressively replace alcohol calories
- Year 2 onwards: Weight tends to plateau as the alcohol-reduction trajectory flattens
This is not a weight-loss programme. It’s the side-effect of treating alcohol use disorder for patients who happened to be drinking enough that the alcohol calories were significant. If your goal is specifically weight loss, naltrexone alone is the wrong tool; established weight-management approaches (calorie tracking, exercise, GLP-1 agonists if appropriate) are better-suited.
If your goal is reducing alcohol intake AND you’d welcome the weight loss as a side effect, naltrexone for alcohol use disorder will likely deliver both. The weight loss isn’t the primary win; the alcohol reduction is.
# How AlcoLog tracks the connection
AlcoLog logs every drink with calorie counts auto-filled from the catalogue (273 drinks across 87 size presets, with editable values if you customise pours). The session-end review shows total calories from alcohol per session, and the History view’s monthly cards show monthly alcohol calories alongside drinks, units, and cost.
For patients tracking weight loss alongside drinking reduction, the trend graph in History lets you select “calories” as the metric and see your alcohol-calorie trajectory over months. This is the side of the equation naltrexone affects directly; you’ll need a separate tool for food calories and weight if you want a complete picture.
AlcoScore deliberately excludes medication use from its scoring. Your dose log informs you, not your score. Data stays on your device. CSV export of your last 10 sessions is free; unlimited export and PDF reports are on Pro.
