Ozempic, Wegovy, Mounjaro: How BMI Determines Eligibility

Every time another celebrity opens up about Ozempic, Wegovy, or Mounjaro, search volume for "GLP-1 weight loss" surges. The headlines are about people; the medical reality is about a number — body mass index. BMI is the first column on the prescribing flowchart for every one of these drugs. If you are considering them, the BMI Calculator is the first measurement you and your doctor will use.

What GLP-1 medications actually are

GLP-1 receptor agonists mimic glucagon-like peptide-1, a hormone your body releases after meals. They reduce appetite by signaling fullness to the brain, slow stomach emptying so you stay full longer, and improve insulin response. Four names dominate the US conversation:

• Ozempic (semaglutide) — FDA-approved for type 2 diabetes, by Novo Nordisk.
• Wegovy (semaglutide, higher dose) — FDA-approved for chronic weight management, by Novo Nordisk.
• Mounjaro (tirzepatide) — FDA-approved for type 2 diabetes, by Eli Lilly.
• Zepbound (tirzepatide) — FDA-approved for chronic weight management, by Eli Lilly.

Same molecule under two brand names per maker — the difference is dosing protocol and FDA indication.

BMI thresholds that determine eligibility

FDA labeling for the chronic weight management indication (Wegovy, Zepbound) is explicit. To qualify on-label, an adult patient needs:

• BMI 30 or higher (the obesity threshold), OR
• BMI 27 or higher with at least one weight-related comorbidity — type 2 diabetes, hypertension, dyslipidemia, or obstructive sleep apnea.

That is the entire eligibility gate at the labeling level. Insurance coverage and physician judgment add layers, but BMI is the first hurdle every time. Calculate yours in 30 seconds with our free BMI Calculator.

What realistic results look like

Social media versions of GLP-1 results are extreme outliers. Peer-reviewed clinical trial numbers are more sober:

• Wegovy (semaglutide 2.4 mg) — STEP-1: ~15% mean body weight loss at 68 weeks vs 2.4% on placebo.
• Zepbound (tirzepatide 15 mg) — SURMOUNT-1: ~21% at 72 weeks vs 3.1%.
• Ozempic (semaglutide 1.0 mg) — typically 6 to 8% at 68 weeks.

A 100 kg adult at BMI 35 dropping 15% lands at 85 kg and BMI ~29.7 — out of obese into overweight. Plan for trial averages; treat anything beyond as upside.

The tracking workflow during treatment

If you start a GLP-1, here is the BMI-related monitoring most clinicians use:

• Baseline: BMI, waist circumference, blood pressure, fasting glucose, HbA1c.
• Weekly: weigh in same day, same time, same conditions. Calculate BMI; track the trend.
• Monthly: waist circumference. Visceral fat reduction drives much of the metabolic benefit.
• Quarterly: bloodwork.
• Annually: review with your doctor.

BMI normalizes for height and is comparable across months — easier to reason about than raw kilograms. See our companion piece Why You Should Track Your BMI: What the CDC Recommends.

Side effects and the realistic downside

GLP-1s are not free of trade-offs:

• Nausea — 30-45% of patients, peaks at dose increases.
• Vomiting and diarrhea — 15-25%.
• Constipation — 10-20%.

Less common but serious: pancreatitis, gallbladder issues, kidney problems from severe dehydration. Black-box warning for thyroid C-cell tumors based on rodent studies — contraindication in patients with personal/family history of medullary thyroid carcinoma or MEN 2.

What happens if you stop the medication

Most patients regain a substantial portion of lost weight within 12 months of stopping. STEP-4 measured roughly two-thirds regain over a year off semaglutide. This is why guidelines have shifted toward treating GLP-1s as long-term medications — similar to blood pressure or cholesterol drugs — rather than short courses with a clean exit.

If long-term medication is not what you want, structured dietary change, strength training, sleep, and (for some) bariatric surgery remain real paths. The 5-10% body weight loss that produces measurable health improvements is achievable without medication; it just takes 6-12 months and a sustained habit shift.

Whether GLP-1s are right for you or not, BMI tracking belongs in the conversation either way. The number is free, fast, and the universal common language across every clinic, every guideline, every research paper.