RxGuide
Condition Guide

Medications for Obesity

ICD-10: E66

Medically Reviewed by Dr. Sarah Chen, PharmD, BCPS

Clinical Pharmacist & Medical Reviewer

Last reviewed: March 19, 2026

Key Takeaways

  • GLP-1 receptor agonists (semaglutide, tirzepatide) represent a paradigm shift in obesity pharmacotherapy — achieving 15–22% body weight loss, approaching bariatric surgery outcomes.
  • FDA-approved weight loss medications are indicated for BMI ≥30, or BMI ≥27 with a weight-related comorbidity (diabetes, hypertension, sleep apnea).
  • All pharmacological treatments for obesity should be combined with lifestyle intervention (caloric restriction, increased physical activity) for maximum benefit.
  • Weight regain is common after stopping anti-obesity medications — many patients require long-term or indefinite treatment.
  • Orlistat is the only FDA-approved weight loss medication available over the counter (Alli 60 mg); prescription strength is 120 mg (Xenical).

Overview

Obesity affects 42% of American adults and is a major risk factor for type 2 diabetes, cardiovascular disease, sleep apnea, and certain cancers. It is now recognized as a chronic disease requiring long-term management.

Treatment Overview

Treatment includes intensive lifestyle intervention, behavioral therapy, pharmacotherapy, and bariatric surgery for severe cases. GLP-1 receptor agonists represent a major advance in pharmacological treatment.

7

Total Medications

3

Drug Classes

1

Off-Label Uses

Drug Classes for Obesity

Pharmacist-reviewed overview of each medication class, how it works, and when it's used.

GLP-1 Receptor Agonists

GLP-1 RAs

First-Line

Mechanism of Action

Activate glucagon-like peptide-1 receptors in the hypothalamus, reducing appetite and food intake. Also slow gastric emptying, increasing satiety. At higher doses used for obesity (vs. diabetes), the weight loss effect is more pronounced.

Common Examples

Semaglutide 2.4 mg (Wegovy)Liraglutide 3.0 mg (Saxenda)

Clinical Notes

Semaglutide (Wegovy) achieves ~15% body weight loss at 68 weeks (STEP 1 trial). The SELECT trial showed semaglutide reduced major cardiovascular events by 20% in obese patients with established CVD. Liraglutide achieves ~8% weight loss.

Common Side Effects

  • Nausea and vomiting (dose-dependent, usually transient)
  • Diarrhea
  • Constipation
  • Pancreatitis (rare)
  • Thyroid C-cell tumors (rodent data; avoid in personal/family history of MEN2 or medullary thyroid cancer)

GIP/GLP-1 Dual Receptor Agonists

Twincretins

First-Line

Mechanism of Action

Activate both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors simultaneously. The dual mechanism produces greater appetite suppression and weight loss than GLP-1 agonism alone.

Common Examples

Tirzepatide 15 mg (Zepbound)

Clinical Notes

Tirzepatide (Zepbound) achieves ~22% body weight loss at 72 weeks (SURMOUNT-1 trial) — the greatest weight loss of any approved pharmacotherapy. FDA-approved for obesity in 2023. Also approved as Mounjaro for type 2 diabetes.

Common Side Effects

  • Nausea and vomiting
  • Diarrhea
  • Constipation
  • Pancreatitis (rare)
  • Thyroid C-cell tumors (same caution as GLP-1 RAs)

Combination Phentermine/Topiramate

Qsymia

First-Line

Mechanism of Action

Phentermine is a sympathomimetic that suppresses appetite by releasing norepinephrine. Topiramate reduces appetite through multiple mechanisms including GABA modulation and carbonic anhydrase inhibition.

Common Examples

Phentermine/topiramate ER (Qsymia)

Clinical Notes

Achieves ~10% body weight loss. Lower cost than GLP-1 agonists. Contraindicated in pregnancy (topiramate is teratogenic — oral contraception required). Schedule IV controlled substance due to phentermine component.

Common Side Effects

  • Dry mouth
  • Constipation
  • Insomnia
  • Cognitive slowing (topiramate)
  • Elevated heart rate
  • Teratogenic — contraindicated in pregnancy

Naltrexone/Bupropion

Contrave

Second-Line

Mechanism of Action

Bupropion activates pro-opiomelanocortin (POMC) neurons in the hypothalamus, reducing appetite. Naltrexone blocks the autoinhibitory feedback on POMC neurons, enhancing bupropion's effect.

Common Examples

Naltrexone/bupropion ER (Contrave)

Clinical Notes

Achieves ~5–8% body weight loss. Useful in patients with comorbid depression or tobacco use disorder (bupropion treats both). Contraindicated in patients with seizure disorders, bulimia, or taking opioids.

Common Side Effects

  • Nausea
  • Constipation
  • Headache
  • Elevated blood pressure and heart rate
  • Seizure risk (bupropion)

Orlistat

Orlistat

Second-LineGeneric Available

Mechanism of Action

Inhibits pancreatic and gastric lipases, preventing absorption of approximately 30% of dietary fat. The unabsorbed fat is excreted in the stool.

Common Examples

Orlistat 120 mg (Xenical)Orlistat 60 mg OTC (Alli)

Clinical Notes

Achieves ~3–5% body weight loss — modest compared to newer agents. The only FDA-approved weight loss medication available OTC. Also reduces LDL cholesterol and may reduce risk of type 2 diabetes.

Common Side Effects

  • Oily or fatty stools
  • Fecal urgency and incontinence
  • Oily spotting
  • Flatulence with discharge
  • Fat-soluble vitamin malabsorption (supplement A, D, E, K)

All Medications

FDA-approved and commonly used medications for Obesity in our database.

How to Choose the Right Medication

Clinical decision factors used by prescribers when selecting a treatment.

  1. 1For patients with obesity and type 2 diabetes: tirzepatide (Zepbound/Mounjaro) or semaglutide (Wegovy/Ozempic) — treat both conditions simultaneously.
  2. 2For patients with obesity and established cardiovascular disease: semaglutide (Wegovy) — the SELECT trial showed 20% reduction in MACE.
  3. 3For patients with obesity and depression or tobacco use disorder: naltrexone/bupropion (Contrave) addresses multiple conditions.
  4. 4For patients seeking an oral option: phentermine/topiramate (Qsymia) or naltrexone/bupropion (Contrave) — both are oral; GLP-1 agonists are injectable.
  5. 5For patients with cost constraints: phentermine alone (generic, very inexpensive) is FDA-approved for short-term use; orlistat OTC (Alli) is available without a prescription.
  6. 6Always combine pharmacotherapy with a caloric deficit of 500–750 kcal/day and at least 150 minutes of moderate-intensity physical activity per week.

Monitoring & Follow-Up

  • Weigh monthly; assess response at 16 weeks — if <5% weight loss, consider switching or adding another agent.
  • Monitor blood pressure and heart rate (phentermine/topiramate and naltrexone/bupropion can increase both).
  • For GLP-1 agonists: monitor for GI side effects; titrate dose slowly to improve tolerability.
  • Reassess cardiovascular risk factors (lipids, blood pressure, HbA1c) every 3–6 months.
  • Screen for eating disorders before initiating pharmacotherapy.

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Frequently Asked Questions

What BMI is considered obese?

A BMI of 30 or higher is classified as obese. Class I obesity: BMI 30–34.9. Class II: BMI 35–39.9. Class III (severe): BMI ≥ 40.

Will I regain weight when I stop GLP-1 medications?

Yes — weight regain is common after stopping GLP-1 receptor agonists. The STEP 4 trial showed that patients who stopped semaglutide after 20 weeks regained approximately two-thirds of their lost weight within 1 year. This is because obesity is a chronic condition driven by biological factors (hormones, genetics, metabolism) that persist after stopping medication. Many patients require long-term or indefinite treatment, similar to how hypertension requires ongoing antihypertensive therapy.

Is bariatric surgery better than GLP-1 medications for weight loss?

Bariatric surgery (Roux-en-Y gastric bypass, sleeve gastrectomy) typically achieves 25–35% total body weight loss — more than any medication. However, surgery carries perioperative risks and requires lifelong dietary changes. Tirzepatide (Zepbound) now achieves ~22% weight loss, approaching sleeve gastrectomy outcomes in clinical trials. For patients who are not surgical candidates or prefer to avoid surgery, tirzepatide represents a compelling alternative. The choice depends on individual risk factors, preferences, and access.

References & Clinical Sources

  1. 1.Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002.
  2. 2.Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216.
  3. 3.Lincoff AM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med. 2023;389(24):2221-2232.
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Medical Disclaimer

The information on RxGuide is intended for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician, pharmacist, or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.