Short answer: Contrave (naltrexone and bupropion) is a tablet for long-term weight management, stepped up over 4 weeks to 2 tablets twice daily, with a boxed warning about suicidal thoughts and behaviors.1 Phentermine, here from the Lomaira 8 mg label, is for short-term use of a few weeks, and its label gives it as Schedule IV.2 Neither label reports a trial of one against the other.
| Contrave | Phentermine (Lomaira) | |
|---|---|---|
| What is in it | Naltrexone 8 mg and bupropion 90 mg per extended-release tablet1 | Phentermine hydrochloride 8 mg per scored tablet2 |
| Length of use | Long term1 | A few weeks2 |
| Label dose | 1 tablet a day in week 1, rising to 2 tablets twice daily from week 41 | 8 mg three times a day, half an hour before meals2 |
| Weight loss in label trials | COR-I, 56 weeks: −5.4% vs −1.3% on placebo; 42% vs 17% lost at least 5%1 | Appetite suppressants added only a fraction of a pound a week over placebo in short trials2 |
| When to stop | Under 5% weight loss after 12 weeks on the full dose1 | If tolerance develops, stop rather than raise the dose2 |
| Common side effects | Nausea 32.5% vs 6.7% on placebo; constipation 19.2% vs 7.2%; headache 17.6% vs 10.4%1 | Listed without rates: fast heartbeat, raised blood pressure, insomnia, dry mouth, restlessness2 |
| Controlled substance | No schedule listed1 | Schedule IV2 |
| Missed dose | Wait until the next scheduled dose; no more than 1 dose at a time1 | No rule in the label2 |
| Boxed warning | WARNING: SUICIDAL THOUGHTS AND BEHAVIORS1 | None2 |
Both can raise blood pressure and heart rate: Contrave is not used with uncontrolled high blood pressure and has blood pressure and pulse checked, and Lomaira is used with caution even with mild high blood pressure.12 Neither is used within 14 days of an MAOI. Both say people with diabetes on insulin or other diabetes medicines may need those doses lowered. Contrave's label says to minimize or avoid alcohol; Lomaira's says alcohol may cause an adverse reaction.12
Contrave contains bupropion, so its warnings include suicidal thoughts, mood changes, seizures (about 0.1% vs 0% on placebo) and mania, and its naltrexone blocks opioids, so it is not used with long-term opioids. About 24% on Contrave and 12% on placebo stopped because of side effects.1 Lomaira's warnings include rare primary pulmonary hypertension and heart valve disease, abuse and dependence, and it advises against combining it with other weight-loss drugs.2 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Which, if either, fits is for your prescriber. More detail: Contrave side effects, Lomaira side effects, the Contrave and Lomaira dosing schedules, the Contrave missed-dose page, the naltrexone-bupropion and phentermine guides, and Contrave vs Qsymia: how do the two weight-loss pills compare?.