Obesity Pharmacotherapy: Semaglutide, Tirzepatide, and Combination Approaches
Semaglutide 2.4 mg: The STEP Program
Semaglutide 2.4 mg weekly (Wegovy) achieved mean weight loss of 14.9% versus 2.4% for placebo at 68 weeks in the STEP 1 trial (n=1,961). The STEP 2 trial in patients with type 2 diabetes showed 9.6% weight loss. STEP 3 combined semaglutide with intensive behavioral therapy, achieving 16.0% weight loss. Importantly, the STEP 4 withdrawal trial demonstrated weight regain of two-thirds of lost weight within 1 year of discontinuation, establishing the chronic nature of obesity pharmacotherapy. The SELECT cardiovascular outcomes trial (n=17,604) showed semaglutide reduced major adverse cardiovascular events (MACE) by 20% (HR 0.80, 95% CI 0.72-0.90) in overweight/obese patients with established CVD but without diabetes.
Tirzepatide: The SURMOUNT Program
Tirzepatide (Zepbound), a dual GLP-1/GIP receptor agonist, demonstrated superior weight loss across the SURMOUNT program. SURMOUNT-1 (n=2,539) showed dose-dependent weight loss: 15.0% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg versus 3.1% for placebo at 72 weeks. SURMOUNT-2 in patients with type 2 diabetes achieved 14.7% weight loss at the 15 mg dose. SURMOUNT-3, combining tirzepatide with an intensive 12-week lead-in behavioral program, achieved total weight loss of 26.6% at 72 weeks. The percentage of patients achieving 20% or more weight loss was 36% at 15 mg in SURMOUNT-1, approaching outcomes previously achievable only with bariatric surgery.
Other Approved Agents
Phentermine-topiramate ER (Qsymia) at the maximum dose (15/92 mg) achieves 9.8% weight loss at 56 weeks (EQUIP trial) and remains cost-effective for patients without insurance coverage for injectable agents. Naltrexone-bupropion (Contrave, 32/360 mg daily) provides 5-6% weight loss and may be particularly beneficial for patients with food craving-driven eating behavior. Orlistat 120 mg TID achieves modest weight loss (3-4% over placebo) but is limited by gastrointestinal side effects. Liraglutide 3.0 mg daily (Saxenda) achieves 8% weight loss but has been largely supplanted by semaglutide given the latter's superior efficacy and weekly dosing convenience.
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Emerging Combination and Next-Generation Therapies
Retatrutide, a triple GLP-1/GIP/glucagon receptor agonist, achieved unprecedented weight loss of 24.2% at 48 weeks at the highest dose (12 mg) in the phase 2 trial (n=338). The glucagon component adds energy expenditure stimulation to the appetite suppression of GLP-1/GIP agonism. Orforglipron, an oral non-peptide GLP-1 receptor agonist, demonstrated 14.7% weight loss at 36 weeks in the phase 2 ACHIEVE trial, potentially addressing injection aversion. CagriSema (cagrilintide plus semaglutide) combines amylin and GLP-1 agonism, with phase 2 data showing 15.6% weight loss at the 2.4 mg/2.4 mg dose at 32 weeks, and the phase 3 REDEFINE program is ongoing.
Patient Selection and Practical Management
Anti-obesity medications are indicated for BMI at or above 30, or BMI at or above 27 with at least one weight-related comorbidity. GLP-1 RA and dual agonists are preferred first-line agents given superior efficacy and cardiovascular benefit data. Dose titration should follow label-recommended schedules to minimize GI adverse effects: nausea (40-44%), diarrhea (30%), and vomiting (24%) are generally transient, resolving within 4-8 weeks of stable dosing. Contraindications include personal or family history of medullary thyroid carcinoma or MEN2. Monitor for gallbladder disease (cholelithiasis risk increases with rapid weight loss) and ensure adequate protein intake (1.2 g/kg/day) with resistance training to preserve lean mass during pharmacotherapy-induced weight loss.
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