FDA-approved anti-obesity medications now produce 5 to 21 percent body weight loss at one year. The major classes are GLP-1 agonists, GIP/GLP-1 agonists, sympathomimetics, naltrexone-bupropion, lipase inhibitors, MC4R agonists, and a hydrogel device. Most require BMI 30 or higher, or 27 or higher with a weight-related condition. Choice depends on effectiveness, side effects, cost, route, and medical history.
Why Obesity Pharmacotherapy
Lifestyle change alone produces 3 to 8 percent weight loss for most adults but is difficult to sustain — most participants in intensive lifestyle trials regain 30 to 50 percent of lost weight within 2 years. Anti-obesity medications can roughly double the weight loss achievable with lifestyle alone and help sustain it long-term. AACE and ACE recognize obesity as a chronic disease deserving chronic treatment.
Treatment is justified by the link between obesity and major comorbidities — type 2 diabetes, hypertension, dyslipidemia, sleep apnea, fatty liver disease, joint disease, certain cancers, and cardiovascular events. Modest weight loss (5 to 10 percent) reliably improves blood pressure, lipids, A1C, and quality of life.
FDA-Approved Anti-Obesity Medications
| Drug | Brand | Class | Route | Year Approved |
|---|---|---|---|---|
| Tirzepatide | Zepbound | GIP/GLP-1 dual agonist | Weekly injection | 2023 |
| Semaglutide | Wegovy | GLP-1 receptor agonist | Weekly injection | 2021 |
| Liraglutide | Saxenda | GLP-1 receptor agonist | Daily injection | 2014 |
| Phentermine + topiramate | Qsymia | Sympathomimetic + anticonvulsant | Daily pill | 2012 |
| Naltrexone + bupropion | Contrave | Opioid antagonist + antidepressant | Twice-daily pill | 2014 |
| Phentermine | Adipex-P, Lomaira | Sympathomimetic | Daily pill | 1959 |
| Orlistat | Xenical (Rx), Alli (OTC) | Lipase inhibitor | With each fat-containing meal | 1999 |
| Setmelanotide | Imcivree | MC4R agonist | Daily injection | 2020 |
| Plenity (device) | Plenity | Hydrogel medical device | Capsules with water before meals | 2019 (FDA cleared) |
Class 1 — GLP-1 and Dual GIP/GLP-1 Agonists
The most effective anti-obesity drugs available. They mimic gut hormones that signal satiety to the brain and slow gastric emptying. Weight loss in trials:
- Tirzepatide (Zepbound) — ~21% at 72 weeks (SURMOUNT-1)
- Semaglutide (Wegovy) — ~15% at 68 weeks (STEP-1)
- Liraglutide (Saxenda) — ~8% at 56 weeks (SCALE)
Common side effects: nausea, vomiting, diarrhea, constipation, abdominal pain (usually early and tapering); rare pancreatitis, gallbladder events, and thyroid C-cell concerns (boxed warning). Cost is substantial — roughly $1,000 to $1,350 per month at cash list price.
Class 2 — Sympathomimetics
Older central nervous system stimulants that suppress appetite by releasing norepinephrine.
- Phentermine (Adipex-P, Lomaira) — 5 to 8 percent at 12 weeks; Schedule IV
- Qsymia (phentermine + topiramate) — 8 to 10 percent at 1 year
Common side effects: dry mouth, insomnia, palpitations, anxiety, modest BP and HR rise. Qsymia adds paresthesia, altered taste, cognitive slowing, and topiramate teratogenicity (contraindicated in pregnancy). Phentermine is inexpensive (under $30 per month generic); Qsymia runs about $98 to $200 per month with manufacturer programs.
Class 3 — Naltrexone + Bupropion (Contrave)
Targets both appetite (POMC neurons) and food reward (mesolimbic dopamine). Weight loss of 5 to 9 percent at 1 year (COR trials).
Common side effects: nausea (most common), constipation, headache, insomnia. Carries a boxed warning for suicidality (bupropion class warning, mostly for younger adults). Contraindicated in seizure disorder, uncontrolled hypertension, current opioid use, MAOI use, and eating disorders.
Class 4 — Lipase Inhibitor (Orlistat)
Blocks about 30 percent of dietary fat absorption. Weight loss 3 to 4 percent at 1 year (net of placebo). The only anti-obesity drug with OTC availability (Alli 60 mg). XENDOS trial showed 37 percent reduction in T2D progression in prediabetes.
Side effects are GI: oily stools, fecal urgency, flatulence with discharge. Daily multivitamin recommended. Drug interactions with cyclosporine, levothyroxine, warfarin.
Class 5 — MC4R Agonist (Imcivree)
Only for specific genetic obesity disorders (POMC, PCSK1, LEPR deficiency, Bardet-Biedl syndrome). Daily subcutaneous injection. Weight loss 8 to 25 percent depending on the specific genetic diagnosis. Side effects: injection-site reactions, skin hyperpigmentation, spontaneous penile erections, mood changes. List price about $300,000 per year.
Class 6 — Medical Device (Plenity)
Cellulose hydrogel that absorbs water and expands in the stomach. Approved for BMI 25 to 40. Weight loss about 6 percent at 6 months. Side effects are mild — bloating, gas, mild abdominal discomfort. Not absorbed systemically. About $98 per month through manufacturer telehealth.
Effectiveness Comparison
| Medication | Average Weight Loss | Route | Typical Cash Cost |
|---|---|---|---|
| Tirzepatide (Zepbound) | ~21% | Weekly injection | ~$1,000/mo |
| Semaglutide (Wegovy) | ~15% | Weekly injection | ~$1,350/mo |
| Qsymia | ~8-10% | Daily pill | ~$98-200/mo |
| Liraglutide (Saxenda) | ~8% | Daily injection | ~$1,300/mo |
| Contrave | ~5-9% | 2x daily pill | ~$99-700/mo |
| Phentermine | ~5-8% (12 wk) | Daily pill | ~$10-30/mo |
| Plenity (device) | ~6% | Capsules before meals | ~$98/mo |
| Orlistat (Xenical) | ~6-10% | With fat meals | ~$200-700/mo |
| Orlistat (Alli OTC) | ~5% | With fat meals | ~$50/mo |
| Imcivree | ~8-25% (genetic) | Daily injection | ~$25,000/mo |
How Clinicians Choose
The 2016 AACE/ACE clinical practice guidelines (and ongoing updates) suggest individualizing choice based on:
- Target weight loss — patients needing more than 10 percent typically benefit from GLP-1-based therapy
- Comorbidities — type 2 diabetes favors GLP-1 RAs or tirzepatide; CV disease favors Wegovy (SELECT trial showed CV benefit)
- Side-effect tolerance — GI sensitivity vs CNS effects guides choice
- Route preference — pill vs injection
- Cost and insurance — generic phentermine vs brand-name injectables
- Pregnancy planning — Qsymia teratogenic; all anti-obesity drugs avoided in pregnancy
- Drug interactions — opioid use rules out Contrave; cardiovascular disease limits sympathomimetics
- Mental health history — Contrave suicidality warning, Qsymia mood/cognitive effects
Choosing Among Newer GLP-1 Agents
For deeper comparisons, see our pillar pieces on Wegovy vs Ozempic, Zepbound vs Wegovy, tirzepatide vs semaglutide, and Saxenda vs Wegovy.
Reassessment Milestones
| Time on Medication | Assessment | Decision |
|---|---|---|
| 4 weeks | Tolerance, side effects, initial weight change | Adjust dose, manage side effects |
| 12-16 weeks | Weight loss of 4-5%? | Continue if yes; reconsider if no |
| 1 year | Comorbidity outcomes, sustained weight loss | Long-term plan, dose maintenance |
| Ongoing | Annual review of risks, benefits, alternatives | Continue, switch, or step down |
Insurance Coverage Landscape
Commercial insurance increasingly covers anti-obesity medications with prior authorization documenting BMI, comorbidities, prior diet attempts, and sometimes a documented period of supervised lifestyle change. Medicare Part D historically excludes anti-obesity drugs (a holdover from a 2003 law); legislative efforts (the Treat and Reduce Obesity Act) have been proposed for many years to change this. State Medicaid programs vary widely. Manufacturer assistance programs and direct-to-consumer telehealth options (Contrave $99/month, Qsymia $98/month, Plenity $98/month, Eli Lilly Direct Zepbound program) have expanded access for cash-paying patients.
The Pipeline
Several next-generation drugs are in late-stage development:
- Retatrutide — triple agonist (GIP, GLP-1, glucagon); phase 2 weight loss approaching 24%
- Orforglipron — oral non-peptide GLP-1; potentially first oral with injection-level efficacy
- CagriSema — cagrilintide (amylin) plus semaglutide; phase 3 weight loss in 15-20% range
- Bimagrumab — myostatin pathway, focus on fat loss with muscle preservation
- Survodutide — GLP-1/glucagon dual agonist
Anti-Obesity Medication and Prediabetes
For patients with prediabetes, the goal of anti-obesity treatment includes preventing progression to type 2 diabetes. Evidence supports:
- Lifestyle change as foundational — DPP showed 58 percent reduction in T2D incidence
- Metformin — DPP showed 31 percent reduction
- Orlistat — XENDOS showed 37 percent reduction over 4 years
- Liraglutide — SCALE-Prevention showed 79 percent reduction over 3 years
- Semaglutide — STEP-5 and STEP-Diabetes Prevention data emerging
- Bariatric surgery — most powerful intervention for diabetes prevention and remission
Five to ten percent weight loss reliably improves insulin sensitivity, lowers fasting glucose, and shifts many people out of the prediabetes A1C range.
Practical Considerations
- Medication is most effective combined with structured lifestyle change.
- Plan for side-effect management, especially early.
- Reassess at 12 to 16 weeks; switch or stop if response is inadequate.
- Address pregnancy plans and contraception before starting teratogenic options (Qsymia).
- Document baseline labs (CBC, CMP, lipids, A1C, TSH where relevant) and follow.
- Long-term treatment is increasingly the standard — obesity is chronic.
Related Reading
For agent-specific detail, see our pieces on Qsymia, Contrave, phentermine, orlistat, Plenity, and Imcivree. Also see our pillar on treatment options and our explanation of whether prediabetes is reversible.
The Bottom Line
FDA-approved anti-obesity medications now span six classes and produce 5 to 21 percent body weight loss at one year. GLP-1 and dual GIP/GLP-1 agonists (tirzepatide, semaglutide, liraglutide) lead in effectiveness; oral combinations (Qsymia, Contrave) reach 5 to 10 percent at lower cost; older agents (phentermine, orlistat) remain useful niches; Imcivree treats specific rare genetic obesity; Plenity is a device option for milder cases. Choice depends on effectiveness goals, comorbidities, side-effect tolerance, route, and cost. Long-term continuation is increasingly standard because obesity is chronic. Pair any medication with sustained lifestyle change for the best results, and talk to your doctor about which option fits your medical history and goals.
