Weight Management

Key takeaways

• Four prescription medicines treat obesity or weight-related conditions through three mechanisms: semaglutide (appetite and digestion), orlistat (fat absorption), and the bupropion-naltrexone combination (brain reward and appetite pathways).
• Semaglutide carries a boxed warning for thyroid C-cell tumors seen in animal studies and shouldn't be used by anyone with a personal or family history of medullary thyroid cancer or MEN2.
• Bupropion carries a boxed warning for seizures, with risk rising at higher doses, and it's avoided in anyone with a seizure disorder or an eating disorder history.

How weight-loss medicines work

These drugs act at different points in the system that regulates hunger and fat storage. Semaglutide mimics GLP-1, a gut hormone that slows stomach emptying and reduces appetite signals to the brain. Orlistat blocks an enzyme in the gut that digests fat, so a portion of the fat in a meal passes through undigested instead of being absorbed. Bupropion and naltrexone are combined because they act on separate brain reward and appetite pathways, together reducing hunger and food cravings.

Choosing between semaglutide, orlistat, bupropion and naltrexone

• Semaglutide (also prescribed for diabetes) is a once-weekly injection that slows stomach emptying and reduces appetite, with the dose raised gradually over months to limit nausea. It carries a boxed warning for thyroid C-cell tumors seen in rodent studies and is contraindicated with a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2.
• Orlistat is taken with fat-containing meals and blocks a portion of dietary fat from being absorbed. The main trade-off is digestive side effects, oily spotting or urgent bowel movements, if a meal is higher in fat than the dose accounts for, and it can reduce absorption of fat-soluble vitamins.
• Bupropion, an antidepressant also used for weight management, is usually paired with naltrexone and reduces appetite through brain signaling. It carries a boxed warning for seizures that rises with dose and is avoided in seizure disorders or eating disorders.
• Naltrexone, an opioid blocker, is combined with bupropion to reduce cravings and reward-driven eating. It must not be used alongside opioid painkillers, since it blocks their effect and can trigger withdrawal.

Common questions

Why does semaglutide need such a slow dose increase?

The dose rises gradually, typically over months, because a faster increase causes more nausea and vomiting. The slow schedule gives your digestive system time to adjust to slower stomach emptying.

Can these medicines be combined with each other?

No, aside from the fixed bupropion-naltrexone pairing. Combining separate weight-loss medicines multiplies side effects without added proven benefit, so it isn't standard practice.

Safety essentials

• Semaglutide is contraindicated with a personal or family history of medullary thyroid cancer or MEN2; watch for a new neck lump, hoarseness or difficulty swallowing.
• Bupropion is contraindicated in seizure disorders and eating disorders such as anorexia or bulimia; report any seizure immediately.
• Naltrexone blocks opioid painkillers, so tell every prescriber if you take it, especially before surgery.
• Orlistat can lower absorption of vitamins A, D, E and K; a multivitamin is often taken separately from the dose.
• Seek urgent care for a seizure, severe abdominal pain, or a new lump or swelling in the neck.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.