Medicare Advantage organizations (MAOs) and standalone prescription drug plans (PDPs) largely opted for stability in their formulary designs for 2026, but mounting pressures may force sharper tradeoffs in the years ahead. The first year of Medicare price negotiation under the Inflation Reduction Act (IRA),accelerating GLP-1 utilization, and increasing biosimilar adoption are reshaping formulary economics, even as most plan sponsors limited change amid lingering uncertainty.
Our review of 2026 formularies indicates that large national carriers made modest, targeted adjustments, while smaller and regional plans showed more variability. Across the market, three themes stood out: incremental refinement by large carriers, widening variation in biosimilar strategies, and expansion of coverage for GLP-1s.
Large carriers favor stability with selective recalibration
Large national MAPD sponsors — Centene, CVS/Aetna, Healthcare Services Corp., Humana, and UnitedHealthcare — kept more than 80% of drugs on the same tier as in 2025 and are covering a larger share of drugs in 2026. PDP products mirrored this approach, with roughly 90% of drugs retaining their prior-year tiering. The biggest changes were concentrated in GLP-1 agents, biosimilars, and IRA price-negotiated drugs.
We saw greater variability among smaller and mid-size plans due to differences in custom versus template formularies, total beneficiary cost considerations, prior formulary richness, and the level of focus on tailored Part D strategies.
Biosimilars: broader coverage, divergent playbooks
Coverage for biosimilars is increasing but strategies vary across carriers, most visibly for Humira (adalimumab) and Stelara (ustekinumab).
The Humira market has shifted rapidly as multiple biosimilars and unbranded options entered following the expiration of patent exclusivity three years ago. While all the large national carriers covered Humira in 2025, only Humana and CVS/Aetna are in 2026 with all of the nationals covering at least one biosimilar or unbranded version. When covered, both Humira and its biosimilars are typically placed on specialty tiers. Coverage patterns are largely consistent across MAPD and PDP products, with limited exceptions.
Stelara faces different dynamics. Selected for IRA price negotiation in 2026, it must be covered; however, Part D rules allow substitution with an interchangeable biosimilar. Most carriers added at least one biosimilar, often placing it on a non-specialty tier to improve access relative to the reference product. Stelara’s negotiated status is expected to be temporary, as biosimilar competition will remove it from negotiation eligibility beginning in 2027.
GLP-1s remain a large source of uncertainty GLP-1 agents are among the fastest moving drivers of utilization and cost pressure. Plans are balancing access while managing expanding indications and evolving federal initiatives like the Better Approaches to Lifestyle and Nutrition for Comprehensive Health (BALANCE) Model, a five-year demonstration model aimed at increasing access to GLP-1s in Medicare. Because formularies were set at bid submission in June 2025, ongoing uncertainly will require plans to be vigilant.
Our review of plan formularies revealed some key observations:
- Ozempic and Mounjaro are broadly covered across MAPD and PDP plans. Rybelsus is widely covered in MAPD but less so in PDPs, while Wegovy and Zepbound remain largely excluded.
- Covered GLP-1s are generally placed on preferred brand tiers
- Centene has taken a slightly different path by offering several GLP-1s on enhanced PDPs with low fixed copays.
Looking ahead, Ozempic, Wegovy, and Rybelsus were selected for 2027 price negotiation, requiring coverage next year. Combined with manufacturer negotiations, the voluntary BALANCE model, and a separate GLP-1 demonstration expected to launch in July, access to GLP-1s for weight management is likely to grow through 2026 and 2027, introducing opportunity and financial risk.
Price negotiation reshapes formularies
The 10 drugs selected for the first round of Medicare price negotiations must be covered at a maximum fair price, though plan sponsors retain flexibility over tier placement as long as negotiated drugs are not disadvantaged relative to competitors. We observed that coverage of the 2026 negotiation drugs is broadly consistent across plans.
A few trends stood out in our review of plan formularies:
- Seven negotiated drugs are predominantly placed on tier 3, while three — Enbrel, Imbruvica, and Stelara — remain largely on tier 5. Since manufacturers pulled back on rebates for these drugs, negotiated drugs were much less likely to be positioned on generic or preferred tiers compared to 2025.
- Variation in pre-IRA coverage means negotiated pricing affects plans unevenly, depending on baseline coverage and utilization.
- Drugs selected for 2027 negotiation, such as Wegovy, remain largely excluded today, signaling required coverage expansion ahead.
- Plans are increasingly using coinsurance on tier 3, rising from roughly 38% of general enrollment MAPD plans in 2025 to nearly 59% in 2026, reflecting a shift away from flat copays.
What this means for plan strategy going forward
Change and uncertainty continue to dominate the narrative for Part D. Rising drug costs have become a persistent challenge for Medicare Advantage prescription drug plans and PDPs, requiring carriers and their pharmacy benefit manager partners to reconsider how formularies are structured when bids are developed.
Utilization management through prior authorizations, quantity limits, and step therapies are additional key considerations to managing costs while providing critical care to members, along with net price impacts driven by manufacturer rebates. Similarly, policymakers have a keen focus on initiatives that aim to relieve cost pressures for members, carriers, and the federal government.
For leadership teams, the imperative is clear: success in the next phase of Part D will depend on continuous reassessment, tighter alignment between formulary and financial strategy, and early engagement with partners who can help anticipate policy shifts, model downside risk, and identify sustainable paths forward in an increasingly constrained environment.