Naltrexone for weight loss is taken as a combination tablet with bupropion, with one dose in the morning and one in the evening once you reach the full schedule. You don’t start at the full dose right away. Instead, the medication follows a four-week ramp-up that gradually increases the amount you take, giving your body time to adjust and reducing side effects like nausea.
The Four-Week Dosing Schedule
Each tablet contains a fixed combination of naltrexone and bupropion in extended-release form. The titration works like this:
- Week 1: One tablet in the morning only
- Week 2: One tablet in the morning, one tablet in the evening
- Week 3: Two tablets in the morning, one tablet in the evening
- Week 4 and beyond: Two tablets in the morning, two tablets in the evening
This gradual increase matters. Jumping straight to the full dose significantly raises the chances of nausea, headaches, and trouble sleeping. The slow build lets your body adjust to the medication’s effects on brain chemistry before reaching the target dose of four tablets per day.
Why Meal Timing Matters
You should not take this medication with a high-fat meal. High-fat foods increase how much of the drug your body absorbs, raising exposure levels beyond what’s intended. This is especially relevant for the bupropion component, where higher-than-expected blood levels can increase the risk of seizures. A regular meal or snack is fine, but save the bacon cheeseburger for a different time of day than your dose.
There’s no strict requirement to take it with food versus on an empty stomach, but many people find that taking it alongside a light meal helps reduce the nausea that’s common in the first few weeks.
How the Medication Works
Naltrexone alone isn’t prescribed for weight loss. It works specifically as part of the combination with bupropion, and the two drugs amplify each other’s effects in ways neither achieves on its own.
Your brain has a group of cells in the hypothalamus that regulate hunger and energy use. These cells produce a signaling molecule that tells your body to eat less and burn more energy. They also produce a natural opioid that acts as a brake, dialing their own activity back down. Bupropion stimulates these cells to ramp up their appetite-suppressing signals. Naltrexone blocks the brake mechanism, so those signals keep firing longer and stronger than they would with bupropion alone.
The combination also affects the brain’s reward circuitry. In animal studies, injecting both drugs into the reward center of the brain reduced food intake more than either drug alone. This likely translates to reduced cravings and less reward-driven eating in humans, though the exact mechanism isn’t fully mapped out.
What Results to Expect
In a major clinical trial lasting 56 weeks, people taking the naltrexone/bupropion combination lost an average of 6.4% of their body weight, compared to 1.2% in the placebo group. For someone weighing 220 pounds, that’s roughly 14 pounds versus about 2.5 pounds. The weight loss was already significant at the 28-week mark, with the treatment group down 6.5% compared to 1.9% for placebo.
If you haven’t lost at least 5% of your starting weight by 12 weeks on the full dose, most prescribers will reassess whether continuing makes sense. This medication produces moderate weight loss and works best alongside dietary changes and increased physical activity.
Managing Side Effects Through Timing
Nausea is the most common complaint, particularly during the first few weeks. The gradual dose increase is the primary strategy for managing this, which is why sticking to the titration schedule is important even if you’re eager to see results faster. Most people find the nausea fades as their body adjusts.
Sleep disturbances and increased energy are also reported. If you notice trouble sleeping, the evening dose is typically the culprit. Some prescribers will adjust when you take the second dose, moving it earlier in the evening rather than close to bedtime. Headaches and joint or muscle pain tend to be mild and often resolve on their own within the first month.
What to Do if You Miss a Dose
If you miss a dose, take it as soon as you remember. If it’s almost time for your next scheduled dose, skip the missed one entirely and get back on your regular schedule. Never double up to compensate. Consistency matters for this medication’s effectiveness, but one missed dose won’t derail your progress.
Who Should Not Take It
Because naltrexone is an opioid blocker, anyone currently using opioid medications or substances cannot take it. This includes prescription pain medications, opioid-based cough medicines, and maintenance treatments for opioid dependence. Starting naltrexone while opioids are still in your system can trigger sudden, severe withdrawal. The standard recommendation is to be completely opioid-free before beginning treatment, with at least 7 days of abstinence when possible. Similarly, people in acute alcohol withdrawal should wait until symptoms have resolved, typically a minimum of 3 days.
The bupropion component carries its own restrictions. People with seizure disorders, eating disorders like bulimia or anorexia, or those currently taking other bupropion-containing products should not use this combination.