Obesity Pharmacotherapy: Semaglutide, Tirzepatide, and Combination Approaches
Sam Anderson
Semaglutide 2.4 mg: The STEP Program
The pharmacotherapy of obesity has entered a new era. Semaglutide and tirzepatide have achieved weight loss magnitudes previously associated only with bariatric surgery, fundamentally changing how clinicians think about obesity treatment. For the endocrinologist, primary care physician, or obesity medicine specialist, understanding the comparative efficacy data, practical prescribing considerations, and realistic expectations for weight loss maintenance is essential for integrating these agents into comprehensive obesity management.
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)[1]. The STEP 2 trial in patients with type 2 diabetes showed 9.6% weight loss[9]. 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[4], 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)[3] 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[2]. SURMOUNT-2 in patients with type 2 diabetes achieved 14.7% weight loss at the 15 mg dose[7]. SURMOUNT-3, combining tirzepatide with an intensive 12-week lead-in behavioral program, achieved total weight loss of 26.6% at 72 weeks[8]. The percentage of patients achieving 20% or more weight loss was 36% at 15 mg in SURMOUNT-1[2], 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.
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)[5]. 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[6], 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.
Setting Expectations and the Maintenance Challenge
The most important conversation to have with a patient starting anti-obesity pharmacotherapy is about what happens after the weight comes off. The clinical trial data demonstrate dramatic weight loss during the active treatment phase, but discontinuation studies consistently show that a substantial proportion of lost weight is regained within twelve to twenty-four months of stopping the medication. This is not a failure of willpower — it reflects the biological reality that obesity involves persistent alterations in appetite-regulating hormones and energy homeostasis that reassert themselves when pharmacologic suppression is removed. The practical implication is that anti-obesity medications, like antihypertensives, should be viewed as long-term or indefinite treatments rather than time-limited courses. Patients who achieve meaningful weight loss on semaglutide or tirzepatide should be counseled that the medication is maintaining their weight loss, not just producing it.
Limitations and the Access Crisis
The efficacy of modern anti-obesity pharmacotherapy is undeniable, but the gap between scientific capability and patient access is enormous. Cost remains the dominant barrier — these medications are among the most expensive chronic therapies in medicine, and insurance coverage is inconsistent, with many payers explicitly excluding anti-obesity medications. The supply constraints that have affected semaglutide availability compound the access problem. And the clinical workforce is not yet prepared for the scale of demand: if even a fraction of eligible patients sought treatment, the prescribing, monitoring, and follow-up burden would overwhelm existing capacity. Addressing obesity as a treatable chronic disease rather than a lifestyle choice is the necessary cultural shift, but the healthcare system infrastructure to support that shift at population scale does not yet exist.
References
- Once-Weekly Semaglutide in Adults with Overweight or Obesity PubMed 33567185
- Tirzepatide Once Weekly for the Treatment of Obesity PubMed 35658024
- Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes PubMed 37952131
- Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial PubMed 33752440
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial PubMed 37385275
- Orforglipron (LY3502970), a novel oral non-peptide glucagon-like peptide-1 receptor agonist: a phase 2, randomised, placebo-controlled trial for weight management PubMed 37385276
- Tirzepatide for the Treatment of Obesity in People with Type 2 Diabetes PubMed 37840095
- Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity: the SURMOUNT-3 phase 3 trial PubMed 38409593
- Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): a randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial PubMed 33670037
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