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Stars Navigator · Measure Reference

Medication Adherence for Diabetes Medications, Hypertension (RAS Antagonists), and Cholesterol (Statins)

Three Part D measures that report the percentage of members whose proportion of days covered (PDC) is 80% or higher for the target drug class during the measurement year. Each is calculated by CMS from prescription drug event (PDE) data.

Measure steward

PQA

Data source

Part D PDE

Weighting category

Intermediate outcome

2027 Star weight

3 each

Direction

Higher is better

Period

Calendar year

Specification

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	Diabetes medications	RAS antagonists	Statins
Target drugs	Biguanides, sulfonylureas, thiazolidinediones, DPP-4 inhibitors, GLP-1 receptor agonists, meglitinides, SGLT2 inhibitors	ACE inhibitors, ARBs, the direct renin inhibitor aliskiren, and combination products	All statins, including combination products such as ezetimibe/simvastatin and amlodipine/atorvastatin
Denominator	Members 18 and older with at least two fills of a target drug in the class on different dates of service during the measurement year.
Numerator	Members in the denominator with PDC ≥ 80% for the class across the treatment period.
Measure-specific exclusion	One or more insulin claims	One or more sacubitril/valsartan claims	None beyond shared exclusions
Shared exclusions	Hospice enrollment during the measurement year; end-stage renal disease (ESRD) or dialysis.

Drug lists are summarized by class. Operational work should use the PQA value sets for the applicable measurement year.

Calculation

PDC is days covered divided by days in the treatment period, which runs from the index prescription start date (IPSD) to December 31. Overlapping fills of the same drug are shifted forward, and a day counts as covered when any drug in the class is on hand.

Medication on hand

Jan 1 (IPSD)

Apr

Jul

Oct

Dec 31

Days covered

Uncovered days (18% of period)

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Index prescription start date	Days in treatment period	Covered days required (PDC ≥ 80%)	Allowable uncovered days
January 1	365	292	73
April 1	275	220	55
July 1	184	148	36
October 1	92	74	18

Figure 1. Illustrative member and allowable-gap arithmetic for a non-leap measurement year. Once uncovered days exceed 20% of the treatment period, the member cannot reach PDC ≥ 80% for the year.

Clinical and operational considerations

Insulin initiation removes the member from the diabetes measure for the year. A single insulin claim is sufficient, so members intensifying therapy leave the denominator rather than counting as adherent.
Within-class switches preserve coverage. Moving from an ACE inhibitor to an ARB for cough, or between statins for tolerability, keeps days covered continuous because PDC is calculated at the class level.
Days' supply accuracy matters for injectables. Understated days' supply on GLP-1 pens creates artificial gaps between fills.
Off-benefit fills are invisible. Cash, discount card, and sample supplies are not captured in PDE and present as nonadherence.
Statin-associated muscle symptoms drive discontinuation. Dose reduction, alternate-day dosing, or a hydrophilic statin such as rosuvastatin or pravastatin often allows rechallenge.
The measure misses primary nonadherence. Members who never fill, or fill only once, never enter the denominator, so reported rates overstate population adherence.

Where performance is lost

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Driver	Effect on the measure
Late refills early in the year	Consumes the allowable-gap buffer for every remaining month
Late IPSD	Smaller absolute buffer, as low as 18 days for an October start
30-day supplies	Twelve refill events a year instead of four with 90-day fills
Claims latency	Outreach triggered after the member can no longer reach 80%
Fragmented pharmacy use	No single pharmacy sees the full fill history

Policy watch

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	Change
2027 Star Ratings (MY2025)	Weight 3 for each adherence measure.
2028 Star Ratings (MY2026)	Sociodemographic status (SDS) risk adjustment begins. The update also adds a continuous enrollment requirement and removes the inpatient and SNF stay adjustment. As substantively updated measures, adherence is expected to carry a weight of 1 for this year.
2029 Star Ratings (MY2027)	Expected return to weight 3, within a smaller measure set.
Measure set	Eleven administrative measures are removed across the 2028 and 2029 Star Ratings. Weights are unchanged, so each remaining measure carries a larger share of the summary and overall ratings.
Litigation	Clover v. HHS (S.D. Ga., May 2026). CMS excluded Part D measures from its recalculated 2027 QBP ratings and has appealed to the 11th Circuit. Part D measures remain in the 2027 Star Ratings measure set.

References

CMS. 2027 Star Ratings Measures and Weights.
Pharmacy Quality Alliance. Medication Adherence measure specifications (PDC): Diabetes, RAS Antagonists, Statins.
CMS. Contract Year 2027 Medicare Advantage and Part D Final Rule (CMS-4208-F3), April 2, 2026.
Clover Insurance Co. v. HHS (S.D. Ga., May 27, 2026); CMS memorandum on 2027 Quality Bonus Payment recalculation, June 17, 2026.

Specifications are summarized for education. Consult the PQA measure specifications and CMS Star Ratings Technical Notes for the measurement year in question. Prepared by the MedWatchers clinical pharmacy team, October 2026.