The Medication Possession Ratio (MPR) is the ratio of a patient's drug supply based on pharmacy records to the amount needed for continuous therapy. This can help identify patients who may be nonadherent to drug therapy.


medication possession ratio =

= (number of days covered by drugs received) / (number of days that need to be covered for continuous drug therapy)




< 0.8

poor adherence

0.8 - 1.1

good adherence

> 1.1

excess drug refills


Some causes for poor adherence:

(1) free drug samples

(2) prescription filled at another pharmacy

(3) admitted to the hospital for a prolonged period


Some causes for excess drug refills:

(1) lost medication

(2) change in prescription with excess drug provided

(3) diverting medication (if abuse potential)



• This is a relatively crude screening tool. A person could have filled a prescription and not taken the medication.

• This could be useful for monitoring a patient on a long-term medication at stable dosing.

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