The main finding
In one sentence: Over 56 weeks, adults who took naltrexone/bupropion (Contrave) alongside an intensive behaviour-change program lost an average of 9.3% of their starting weight, compared with 5.1% for those who took placebo with the same program, in the trial's main analysis.
Group averages, not an individual prediction. A trial result describes what happened to a defined group over a defined time.
On this page
Why this study matters
Most weight-loss medicine trials pair the medicine with light lifestyle advice. COR-BMOD asked a different question: what does naltrexone/bupropion add when everyone already receives an intensive behaviour-change program? For Canadian readers, this matters because it shows both what the program alone achieved and how much the medicine added on top. It also reports clearly on side effects and on how many people stopped.
Who was in the study
The trial enrolled 793 adults with overweight or obesity. Their average BMI was 36.5, with a standard deviation of 4.2, which describes how spread out the values were. BMI is weight in kilograms divided by height in metres squared. People with diabetes or major psychiatric illness were excluded. The trial lasted 56 weeks. The published summary does not report ages or where the trial was run.
What the researchers did
This was a randomized, placebo-controlled trial. Randomized means chance decided each person's group. A placebo is an inactive tablet that looks like the medicine. People were assigned in a 1 to 3 ratio: 202 to placebo plus behaviour modification, and 591 to naltrexone sustained-release 32 mg per day combined with bupropion sustained-release 360 mg per day plus behaviour modification. Sustained-release means the tablet releases the medicine slowly.
Both groups were prescribed a reduced-calorie diet and 28 group behaviour-modification sessions. This was the intensive lifestyle part of the trial and it was the same for everyone.
The two main outcomes were percent change in weight and the share of people losing at least 5% of their starting weight at week 56.
The main analysis used a modified intention-to-treat population. This included only people who had at least one weight measurement after the start while still taking the study medicine: 193 in the placebo group and 482 in the medicine group. Missing weights were filled in using each person's last measurement taken while on the medicine, a method called last observation carried forward.
What they found
At week 56, weight loss was 9.3% with naltrexone/bupropion plus behaviour modification and 5.1% with placebo plus behaviour modification (R32-C85). The paper reports this as statistically significant, meaning unlikely to be due to chance. No confidence interval, which is the range within which the true difference would likely fall, was extracted.
The researchers ran two more analyses to test how much the result depended on who was counted:
| Analysis | Naltrexone/bupropion plus program | Placebo plus program |
|---|---|---|
| Main analysis (modified intention to treat) | 9.3% | 5.1% |
| People who completed the trial | 11.5% (301 people) | 7.3% (106 people) |
| Everyone randomized | 7.8% | 4.9% |
The "everyone randomized" figures are lower because they include people who stopped early. The main analysis left out 18.4% of the medicine group who had no weight measurement while on the medicine.
More people in the medicine group than the placebo group lost at least 5% and at least 10% of their starting weight, and the medicine group had greater improvements in markers of heart and metabolic risk. The summary does not give those numbers.
Side effects and people who stopped
Study medicine was stopped by 42.1% of the naltrexone/bupropion group and 41.6% of the placebo group. Side effects were the reason in 25.4% of the medicine group and 12.4% of the placebo group (R32-C86). Nausea was reported more often with naltrexone/bupropion than with placebo. The paper describes the medicine as generally well tolerated.
What this study does not tell you
- The 9.3% figure comes from an analysis that excluded 18.4% of the medicine group. The all-randomized figure of 7.8% is more conservative.
- Filling in missing weights with the last on-medicine measurement can overstate results when many people stop early, as they did here.
- Everyone received 28 group sessions. Results with the medicine and less support are likely to differ.
- People with diabetes or major psychiatric illness were excluded, so results may not apply to them.
- Nearly the same share of people stopped the study medicine in both groups, so the medicine did not reduce dropout overall.
- The percentages cannot be compared with other medicine trials, which used different programs, people and analyses.
- The summary we reviewed does not state who funded the trial.
What it means in Canada
COR-BMOD shows that an intensive behaviour-change program produced meaningful weight loss on its own, and that naltrexone/bupropion added more, at the cost of more side effects. For information on this and other medicines, see the site's medicines pages, including semaglutide in Canada and tirzepatide in Canada. For coverage, see public drug coverage by province. To find behavioural programs, see compare services.
Common questions
How much weight did people lose with naltrexone/bupropion in COR-BMOD?
In the main analysis, 9.3% with naltrexone/bupropion plus behaviour change versus 5.1% with placebo plus the same program at 56 weeks. Counting everyone randomized, it was 7.8% versus 4.9%.
How many people stopped naltrexone/bupropion because of side effects in COR-BMOD?
Side effects led 25.4% of the naltrexone/bupropion group and 12.4% of the placebo group to stop the study medicine.
What was the behaviour-change program in COR-BMOD?
Both groups were prescribed a reduced-calorie diet and 28 group behaviour-modification sessions over 56 weeks.
Related reading
Other studies in this library that bear on the same question.
COR-II: naltrexone/bupropion weight-loss trial
STEP 3: semaglutide with intensive behavioural therapy
SCALE: liraglutide 3 mg weight management trial
Orlistat for one year: results from a UK trial
Source
Original paper: Thomas A Wadden, COR-BMOD, Obesity (Silver Spring, Md.), 2011. PubMed: https://pubmed.ncbi.nlm.nih.gov/20559296/. DOI: https://doi.org/10.1038/oby.2010.147. Funding: The summary we reviewed does not state the funding source. How we summarized it: full text and extracted data.
This page explains a published study. It is not medical advice and does not describe whether a medicine is right for you. Talk to your doctor, nurse practitioner or pharmacist about your own situation. Reviewed and signed by two pharmacists registered in British Columbia, 2026-09-18.
Evidence records behind this page
Each record is a row in the clinical evidence file, taken from the published paper named above. The caution column is the limit the researcher recorded for that number.
This table scrolls sideways.
| Record | What the paper reports | Type | Population | Caution | Source |
|---|---|---|---|---|---|
| R32-C85 | In COR-BMOD, adding naltrexone/bupropion to intensive behavioural support produced mean 56-week weight loss of 9.3% versus 5.1% with placebo plus the same support; the all-randomized sensitivity analysis reported 7.8% versus 4.9%. | direct evidence | Adults with overweight/obesity; diabetes and major psychiatric illness excluded | Modified ITT excluded 18.4% of NB participants lacking an on-drug postbaseline weight; all-randomized results were more conservative. Intensive behavioural support limits transfer to medication-only care. | PubMed 20559296 |
| R32-C86 | Adverse events led to stopping study medication in 25.4% of the naltrexone/bupropion group and 12.4% of the placebo group in COR-BMOD. | direct evidence | Adults with overweight/obesity; diabetes and major psychiatric illness excluded | Modified ITT excluded 18.4% of NB participants lacking an on-drug postbaseline weight; all-randomized results were more conservative. Intensive behavioural support limits transfer to medication-only care. | PubMed 20559296 |