The three measures

Part D includes three medication-adherence measures, each tied to a chronic-disease drug class where staying on therapy clearly drives outcomes:

A member is included in a measure once they fill two or more prescriptions in that therapeutic class during the year. The cohort is built from pharmacy fill data, which means the measure reflects real fill behavior, not what was prescribed on paper. That distinction matters operationally: a member can be perfectly counseled and handed a prescription and still register as non-adherent if they never picked up the second fill. The measure does not see intent. It sees days covered.

How PDC works and why 80% is the line

Each measure is calculated with the proportion of days covered, or PDC. PDC is the share of days in the member's treatment period during which they had the medication on hand, derived from fill dates and days-supply. If a member's PDC is 80% or higher, they count as adherent. The measure score is simply the percentage of eligible members at or above that 80% threshold.

The 80% line is what makes adherence an operations problem rather than a reporting one. Because the denominator is days and the threshold is a hard cutoff, a member can drift from adherent to non-adherent through a few missed refill windows, and once enough days are gone, the 80% mark is mathematically out of reach for the rest of the year. We walk through that arithmetic in detail in our PDC math guide.

80%
PDC threshold: at or above counts a member as adherent
3
Triple-weighted adherence measures: diabetes, RAS antagonists, statins
96%
Medication adherence achieved at our flagship customer

Why they are triple-weighted, and how much they matter

CMS weights intermediate-outcome and outcome measures more heavily than process measures, because they reflect health results rather than activity. The three adherence measures are triple-weighted, which puts them at the top of the weighting scale and makes them roughly a quarter of the Part D summary score in a typical year.

Because Part D has relatively few measures, three triple-weighted measures dominate it. Moving them moves the Part D rating. Missing on them is very hard to offset elsewhere.

The concentration cuts both ways. It means a plan that runs adherence well has a durable advantage that is hard for competitors to copy quickly, because the result is built from months of member behavior rather than a quarter of effort. It also means a plan that lets adherence slip cannot buy its way back with a strong showing on lighter-weight process measures. The arithmetic does not allow it. This is why adherence is usually the first place a serious Stars program invests, and the last place it cuts.

The 2026 single-weight detour, and why it does not change the work

For measurement year 2026, which feeds the 2028 Star Ratings, the three adherence measures are temporarily single-weighted while CMS phases in sociodemographic status (SDS) risk adjustment, which adjusts adherence scoring for factors such as low-income subsidy and dual-eligibility status. They are expected to return to triple-weighting for measurement year 2027, feeding the 2029 Star Ratings. Confirm the exact weight for your measurement year against the current CMS technical notes.

The temptation is to ease off in the single-weight year. That is a mistake. Adherence is built over months of refill behavior, and a member you lose in 2026 does not return on their own when the weight goes back up. Treat the single-weight year as the year you build the capacity, so the team is operating at full effectiveness when triple weighting returns.

There is a second reason not to ease off. The SDS risk adjustment being phased in changes how scores are interpreted for plans with high shares of low-income and dual-eligible members, populations that have historically scored lower on adherence for reasons that have little to do with clinical quality. Building a strong, equitable adherence operation now positions a plan well for the adjusted methodology, not just for the return of the triple weight. The work you do in the build year is the same work that pays off under either weighting.

The operational levers that actually move PDC

Adherence does not respond to a year-end report. It responds to timing. The levers, in order of impact:

  1. Identify members trending below 80% before they fall. Watch fill patterns continuously. A member who is one missed refill from dropping below the line in week 8 is recoverable; the same member in week 40 often is not. Early identification is the whole game.
  2. Refill synchronization. Align a member's chronic-medication refills to the same date so they make one pharmacy trip instead of three. Synchronization is one of the most reliable ways to lift PDC across all three classes at once.
  3. Multi-channel outreach. Reach members on the channel they respond to: SMS reminders, an outbound voice call, or email. A single channel misses the members who do not use it.
  4. Pharmacy coordination. Loop in the dispensing pharmacy for auto-refill enrollment, 90-day supplies where appropriate, and barrier resolution such as cost or transportation.

Notice what these levers have in common: they are all continuous and they all depend on seeing fill data quickly. A 90-day supply only helps if you move the member onto it before they lapse. Refill synchronization only works if you catch the misalignment while there is still runway in the year. None of this is served by a monthly report that arrives weeks after the fill data it summarizes. The teams that move adherence are looking at fill behavior in close to real time and acting on it the same week, not reading about last month's PDC at the next quarterly review.

Where a medication-adherence agent fits

This is repetitive, time-sensitive work that scales badly with headcount and scales well with automation. A medication-adherence agent watches fill data across the panel continuously, flags members trending below 80% while there is still time to recover, and runs the refill reminders and pharmacy coordination across channels. Pharmacists and coordinators then spend their time on the members with real barriers, the ones who need judgment. Our flagship customer reached 96% medication adherence operating this way. The mechanics of what an agent does, step by step, are covered in our breakdown of an AI agent closing a gap.

Adherence is won in the weeks, not at year-end. The measure rewards whoever catches the slip before the 80% line becomes unreachable.

Sources and further reading