Semaglutide & Tirzepatide
Last reviewed: May 2026
GLP-1 receptor agonists (semaglutide, tirzepatide) represent a breakthrough in medical weight management. They work by mimicking the GLP-1 hormone, which reduces appetite, slows gastric emptying, and improves insulin sensitivity.[1] Combined with lifestyle changes, these medications produce significantly more weight loss than diet and exercise alone. This calculator helps estimate your potential weight loss trajectory based on published clinical trial data and your starting weight.
| Time Period | Semaglutide (avg) | Tirzepatide (avg) | Phase |
|---|---|---|---|
| Month 1–2 | 2–4% | 3–5% | Dose titration |
| Month 3–6 | 5–10% | 7–12% | Active loss |
| Month 6–12 | 10–15% | 13–20% | Peak loss phase |
| Month 12–18 | 15–17% | 20–22% | Plateau/maintenance |
GLP-1 (glucagon-like peptide-1) receptor agonists mimic a natural hormone produced in the gut after eating. The natural GLP-1 hormone has a half-life of only 2 to 3 minutes, making it impractical as a medication. Pharmaceutical versions like semaglutide and tirzepatide are engineered with structural modifications that extend their half-life to approximately one week, allowing once-weekly dosing. These medications work through multiple mechanisms simultaneously: they stimulate insulin secretion from the pancreas (lowering blood sugar), suppress glucagon release (reducing liver glucose production), slow gastric emptying (extending feelings of fullness after meals), and act on appetite centers in the brain (reducing hunger and food cravings).
The brain effects are particularly significant for weight loss. GLP-1 receptors in the hypothalamus and brainstem regulate appetite and reward pathways associated with food. Patients consistently report not just reduced hunger but a fundamental shift in their relationship with food: reduced cravings, less preoccupation with meals, and an ability to feel satisfied with smaller portions. Some patients also report reduced interest in alcohol, which is being studied as a potential additional benefit. These neurological effects distinguish GLP-1 medications from previous weight loss drugs that primarily worked through metabolism or fat absorption. For tracking your progress, see our BMI Calculator and Body Fat Calculator.
| Feature | Semaglutide (Wegovy) | Tirzepatide (Zepbound) | Liraglutide (Saxenda) |
|---|---|---|---|
| Mechanism | GLP-1 agonist | GLP-1 + GIP dual agonist | GLP-1 agonist |
| Dosing | Weekly injection | Weekly injection | Daily injection |
| Avg weight loss | 15-17% | 20-22% | 5-8% |
| Titration period | 16-20 weeks | 20 weeks | 5 weeks |
| Max dose | 2.4 mg/week | 15 mg/week | 3.0 mg/day |
| Monthly cost (no insurance) | $900-1,300 | $800-1,100 | $1,200-1,500 |
The most common side effects of GLP-1 medications are gastrointestinal: nausea (affecting 40 to 50 percent of patients), vomiting, diarrhea, and constipation. These effects are most pronounced during dose titration and typically diminish after 4 to 8 weeks at each dose level. Eating smaller meals, avoiding high-fat and greasy foods, staying hydrated, and eating slowly all help manage nausea. Some clinicians prescribe ondansetron (Zofran) for patients experiencing significant nausea during titration.
Maximizing weight loss results while on GLP-1 medications requires attention to protein intake and resistance training. Rapid weight loss from any cause results in loss of both fat and lean muscle mass. Without intervention, approximately 25 to 40 percent of weight lost can come from muscle, which reduces metabolic rate and functional capacity. Consuming 1.2 to 1.6 grams of protein per kilogram of goal body weight daily and performing resistance training two to three times per week preserves muscle mass and ensures that the majority of weight lost is fat. Track your nutritional targets with our Protein Calculator and Calorie Calculator.
The question of duration is central to GLP-1 therapy. Clinical trials show that approximately two-thirds of weight lost is regained within 12 to 18 months of discontinuation, suggesting these medications may require long-term use for sustained results. This raises cost considerations: at $900 to $1,300 per month without insurance, annual expenses can exceed $12,000. Insurance coverage has expanded significantly since 2023, with Medicare Part D beginning to cover semaglutide for obesity in some cases and many commercial plans adding weight management coverage. Employer-sponsored plans increasingly cover anti-obesity medications because the downstream healthcare savings from treating obesity-related conditions (diabetes, heart disease, joint replacement) exceed the medication costs. Compounding pharmacies offer semaglutide at lower prices ($200 to $400 per month) using compounded formulations, though the FDA has raised concerns about quality and consistency of compounded versions. Compare the financial impact using our GLP-1 Savings Calculator.
GLP-1 medications produce the best outcomes when combined with structured lifestyle changes. Clinical trials showing 15 to 22 percent weight loss included dietary counseling and encouraged physical activity as part of the treatment protocol. Patients who exercise regularly while on GLP-1 therapy lose a higher percentage of fat relative to muscle compared to sedentary patients. The reduced appetite from GLP-1 medications creates a natural caloric deficit, but the quality of food consumed still matters: prioritizing protein (1.2 to 1.6 grams per kilogram daily), vegetables, and whole grains over processed foods optimizes body composition outcomes.
Resistance training is particularly important because rapid weight loss from any intervention causes muscle loss alongside fat loss. Studies show that patients performing strength training two to three times per week while on semaglutide preserved 60 to 70 percent more lean mass than those who relied on the medication alone. Cardiovascular exercise improves the metabolic benefits beyond weight loss: insulin sensitivity, blood pressure, lipid profiles, and cardiovascular fitness all improve independently of weight change. A practical weekly exercise plan while on GLP-1 therapy includes three sessions of resistance training, two to three sessions of moderate cardio (walking, cycling, swimming), and daily steps of 7,000 to 10,000 for baseline activity. Monitor caloric needs as weight decreases using our TDEE Calculator and Macro Calculator.
GLP-1 receptor agonists are contraindicated in several populations. Patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 should not use these medications due to thyroid tumor findings in rodent studies. Patients with a history of pancreatitis should use GLP-1 medications with caution because these drugs have been associated with rare cases of acute pancreatitis. Pregnancy is an absolute contraindication; women should discontinue GLP-1 medications at least two months before attempting conception. Patients with severe gastroparesis (delayed stomach emptying) may find symptoms worsened by GLP-1 medications, which further slow gastric emptying. Eating disorders present complex considerations: while GLP-1 medications reduce appetite, they may not address the psychological components of binge eating disorder and should only be prescribed alongside appropriate mental health support. Always discuss your complete medical history with a healthcare provider before starting any weight loss medication. For general health assessment tools, try our Waist-to-Hip Ratio Calculator and Healthy Weight Calculator.
Compounding pharmacies have emerged as a lower-cost alternative to branded GLP-1 medications, offering semaglutide formulations at $200 to $400 per month compared to $900 to $1,300 for brand-name Wegovy. However, compounded medications are not FDA-approved products and quality varies between pharmacies. The FDA has issued warnings about certain compounding pharmacies selling impure or incorrectly dosed semaglutide. Patients considering compounded alternatives should verify that the pharmacy holds state licensure, follows current Good Manufacturing Practices, and provides certificates of analysis for each batch.
→ Combine with protein and exercise. GLP-1 weight loss includes muscle. Resistance training and adequate protein (0.7-1.0g/lb) minimize lean mass loss.[2]
→ Start at the lowest dose. Titrate gradually to manage GI side effects.[1]
→ Track your TDEE. Recalculate with the TDEE Calculator as you lose weight.
→ This is not medical advice. Always work with your prescribing physician for dosing and monitoring.
See also: BMI Calculator · Calorie Deficit · TDEE · Ideal Weight