- A CDC-led study published in the American Journal of Preventive Medicine used linked electronic health records and pharmacy dispensing data from Truveta to analyze 4,027,607 antihypertensive prescriptions among 936,502 US adults with hypertension.
- Compared with 7 am visits, 5 pm visits were associated with 8.8% lower odds of prescription filling and 10.6% lower odds of 90-day medication adherence.
- Later visits were also associated with shorter visits, slightly shorter medication supplies, and lower use of combination pills.
- The findings suggest that time-of-day variation in routine care processes may influence medication management, though the study is observational and does not establish causation.
A new CDC-led study published in the American Journal of Preventive Medicine used linked electronic health records and pharmacy dispensing data from Truveta to examine whether the timing of a primary care visit is associated with antihypertensive prescription filling and short-term adherence. The study found that patients seen later in the clinic day were modestly but consistently less likely to fill their prescriptions and maintain antihypertensive adherence over the following 90 days. Together, the findings suggest that some variation in medication adherence may begin within routine care delivery itself.
How the CDC team studied visit timing and adherence
Researchers from the Centers for Disease Control and Prevention (CDC) studied US adults with hypertension who had an outpatient primary care visit between 2016 and 2024, received an oral antihypertensive prescription, and had a hypertension diagnosis recorded the same day. The analysis included 936,502 patients with 4,027,607 antihypertensive prescription orders written by 14,186 primary care clinicians.
The primary outcomes were prescription filling before the next clinic visit and 90-day medication adherence, measured using linked pharmacy dispensing data. The study also examined visit duration, days’ supply per fill, and use of fixed-dose combination therapy to explore how routine care processes may help explain the relationship between visit timing and adherence.
Later visits linked to lower filling and adherence
The study found a consistent decline in both prescription filling and antihypertensive adherence as visits occurred later in the day. Compared with 7 am visits, 5 pm visits were associated with 10.6% lower odds of 90-day adherence and 8.8% lower odds of prescription filling. Each hour later in the clinic day was associated with 1.0% lower odds of adherence and 0.9% lower odds of filling.
Later visits were also associated with shorter visits, slightly shorter medication supplies, and lower use of combination pills. Together, these patterns suggest that routine care processes may vary as the clinic day progresses.
The researchers also conducted a falsification test to better understand the pattern. The hour-of-visit effect appeared among prescriptions that were filled, but not among those that were not filled. This suggests the difference may be tied more to prescribing and dispensing processes than to patient characteristics alone.
What this signal could mean for public health and evidence teams
Medication adherence is often framed as a patient-level challenge. This study suggests that routine care workflows may also shape what happens after an antihypertensive prescription is written. The per-visit effect is modest, but the authors note that in high-volume primary care, modest differences repeated across millions of visits can add up. For patients who consistently rely on later appointments because of work, caregiving, or transportation constraints, those small gaps may accumulate over time.
For public health leaders and healthcare organizations, the findings point to a practical opportunity to evaluate whether medication management is equally consistent across the clinic day. For life science and evidence teams, the study also highlights the value of linked longitudinal data. Connecting routine clinical encounters with downstream pharmacy behavior makes it possible to study not only what was prescribed, but whether it was filled and sustained afterward.
Read the full study
Clinic Visit Timing, Prescribing Patterns, and Antihypertensive Medication Adherence: Evidence from Linked U.S. Electronic Health Records and Pharmacy Data, American Journal of Preventive Medicine
