Body mass index does not define this market. Coverage does, and the coverage rules turn on comorbidity and on indication rather than on weight.
Prevalence is enormous and largely irrelevant to sizing. Commercial payers require a body mass index threshold plus a comorbidity, or a higher threshold alone, with prior authorisation and step edits on the leading agents. The reimbursable population is therefore anchored on comorbidity-defined segments - obesity with established cardiovascular disease, obesity with type 2 diabetes - and sizing from prevalence rather than from those segments overstates the market by a wide margin.
Medicare is the sharper constraint. Part D excludes anti-obesity medicines prescribed for weight loss, which removes a large population at a stroke. The route in is an outcomes indication rather than a weight-loss one, which is why cardiovascular evidence carries commercial weight here disproportionate to its clinical novelty: it is what converts an excluded product into a covered one.
Negotiation now splits the class asymmetrically. One leading agent faces a negotiated Medicare price across its brand family; the other appears on no selected-drug list. Relative net economics in Medicare will therefore move independently of anything either manufacturer does commercially, and a competitive assessment that treats the two as facing the same pricing environment will be wrong from the date the negotiated price takes effect.
AXLRx obesity reports size the reimbursable comorbidity segments, read the weight-loss and outcomes positions across the class, and model the asymmetric negotiation exposure.
Tirzepatide 20.9% versus semaglutide 15.3% weight loss. The Medicare coverage gap and commercial step-edit reality.
US adult obesity at 41.9% (CDC NHANES). BMI-class distribution, severe-obesity burden, and the comorbidity segments that drive coverage.
Medicare covers Wegovy only for cardiovascular risk, not obesity alone. The IRA's IPAY 2027 semaglutide price applies across the franchise, and ICER returned a 2025 'high value' verdict.
Wegovy lists at roughly $1,349 a month, but CMS pays $274 for a 30-day semaglutide supply from 2027. That 71% cut applies to Ozempic, Rybelsus and Wegovy alike. Tirzepatide sits outside the negotiation entirely, for now.
Wegovy and Zepbound already occupy the injectable position. A new entrant must clear the 20.9% efficacy bar and price beneath the $274 IRA reset arriving in 2027.
Comorbidity, not body mass index alone. US adult obesity prevalence is 41.9%, about 100 million adults, with 9.2% at severe obesity of BMI 40 or above. But commercial payers require BMI of 30 or more plus a comorbidity, or 35 or more on its own, with prior authorisation and step edits on both leading agents. The segments that anchor a reimbursable population are therefore obesity with established cardiovascular disease and obesity with type 2 diabetes, and sizing from prevalence rather than from those segments overstates the market substantially.
Medicare Part D excludes anti-obesity medicines prescribed for weight loss, which removes a large population from the addressable base at a stroke. The exception is Wegovy, covered for cardiovascular-risk reduction following CMS guidance in March 2024; Ozempic, Rybelsus and Mounjaro are covered for type 2 diabetes only. The route into Medicare is therefore an outcomes indication rather than a weight-loss one, which is why the cardiovascular evidence matters commercially as much as the weight-loss data.
Tirzepatide delivers 20.9% weight loss in SURMOUNT-1 against semaglutide's 15.3% in STEP 1, while SELECT showed a 20% reduction in cardiovascular events for semaglutide. ICER's December 2025 review rated both agents high value at current pricing, which is an unusual verdict in a high-cost category and removes cost-effectiveness as the main line of payer attack. List prices run about $1,349 a month for Wegovy and $1,060 for Zepbound.
Asymmetrically, and that is the important structural fact. Semaglutide was selected for IPAY 2027, and its $274 thirty-day maximum fair price applies across Ozempic, Rybelsus and Wegovy from 1 January 2027. Tirzepatide appears on no selected-drug list. One agent in the class faces a negotiated price reset and the other does not, which changes relative net economics in Medicare independently of anything either manufacturer does commercially.
A sizing model built from the comorbidity-defined reimbursable segments rather than from BMI prevalence; competitive intelligence on the weight-loss and cardiovascular-outcomes positions of the leading agents; a payer read covering the Part D exclusion, the cardiovascular-risk route into Medicare, and the commercial prior-authorisation thresholds; and pricing work on the asymmetric IRA exposure across the class. Each is scoped to your asset.