Contrave contains two active ingredients that clear your body at different rates, so the full answer depends on which component you’re tracking. The slower of the two, bupropion, produces metabolites that take roughly 7 to 8 days to fully leave your system after your last dose. Naltrexone, the other ingredient, clears faster, typically within 3 to 4 days.
Half-Lives of Each Ingredient
A drug’s half-life is the time it takes for half of the active substance to be eliminated from your blood. Contrave’s two ingredients, and the active byproducts your liver creates from them, each have their own half-life.
Naltrexone itself has a half-life of roughly 4 to 10 hours, depending on the individual. But your body converts it into an active metabolite that continues working. That metabolite has a half-life of about 12 to 14 hours, meaning it lingers longer than the parent drug.
Bupropion has a half-life of about 21 hours. Its primary active metabolite, hydroxybupropion, has a similar half-life of around 20 hours. Two other active metabolites stick around even longer, with half-lives of 33 to 36 hours. These slower-clearing metabolites are the reason bupropion’s effects persist well after your last pill.
Total Time to Full Clearance
Pharmacologists generally use five to six half-lives as the benchmark for when a drug is essentially gone from your system (about 97% to 99% eliminated). Using that math for each component:
- Naltrexone and its metabolite: With the metabolite’s half-life of 12 to 14 hours, full clearance takes roughly 2.5 to 3.5 days after your last dose.
- Bupropion and its metabolites: The slowest metabolites have half-lives of 33 to 36 hours. Multiplying by five to six half-lives gives you approximately 7 to 9 days for complete elimination.
So if you’re wondering when Contrave is truly out of your system, the practical answer is about one week, possibly a bit longer. That timeline is driven entirely by bupropion’s slow-clearing metabolites.
How Long Until Steady State Builds Up
When you first start Contrave, it takes time for drug levels to stabilize in your body. Naltrexone’s metabolite reaches steady-state concentrations in about 3 days. Bupropion and its metabolites take approximately one week. This is why Contrave is prescribed on a gradual dose-escalation schedule over the first few weeks. The same accumulation timeline works in reverse when you stop: bupropion-related compounds take longer to wash out because they’ve built up to higher levels.
Liver and Kidney Function Change the Timeline
Your liver and kidneys are the two organs responsible for breaking down and removing Contrave’s ingredients. If either one isn’t working at full capacity, the drug stays in your system significantly longer.
Liver impairment has the most dramatic effect on naltrexone. According to FDA prescribing data, people with severe liver impairment had 34 times more naltrexone exposure than those with normal liver function after a single dose. Even mild liver problems nearly tripled exposure. Bupropion exposure roughly doubled in people with moderate liver impairment and was 3.6 times higher in those with severe impairment.
Kidney impairment has a more moderate but still meaningful impact. People with severe kidney impairment had about 2.2 times the exposure to naltrexone’s active metabolite compared to healthy individuals. Bupropion’s metabolites roughly doubled in people with moderate kidney impairment. If you have reduced liver or kidney function, expect Contrave to linger in your system well beyond the standard one-week window.
Other Factors That Slow Clearance
Your liver uses a specific enzyme system to process bupropion. Medications that inhibit this enzyme pathway can slow bupropion breakdown and extend how long it stays active. In one study, a drug that partially blocks this enzyme prolonged the half-life of one bupropion metabolite by 35%. Many common medications interact with this same pathway, so if you’re taking other prescriptions, clearance could take longer than the typical estimate.
Age, body composition, and overall metabolic rate also play a role, though these effects are harder to quantify precisely. Generally, older adults and people with higher body fat may clear the drug somewhat more slowly.
Why the Timeline Matters for Opioid Medications
One of the most common reasons people ask this question is because they need opioid pain medication, either for a planned surgery or an unexpected medical situation. Naltrexone blocks opioid receptors, which means opioid painkillers won’t work properly while naltrexone is still active in your body. Based on naltrexone’s clearance timeline, you’d need at least 3 days, and ideally longer, after your last Contrave dose for opioid medications to function as expected. If you’ve been taking Contrave for months, accumulated drug levels may push that window further out.
This is separate from bupropion, which doesn’t block opioids but does interact with other medications. The full 7 to 9 day clearance window matters if you’re switching to a drug that interacts with bupropion or its metabolites.
Drug Testing Considerations
Standard workplace drug panels do not test for naltrexone or bupropion, so Contrave won’t trigger a positive result on a typical 5-panel or 10-panel screen. However, bupropion has been known to occasionally cause false positives for amphetamines on certain immunoassay-based tests. If this happens, a confirmatory test will distinguish bupropion from actual amphetamines. This possibility exists for the full duration bupropion remains in your system, so up to about a week after your last dose.