Medicines work better if taken, which must be true of migraine prophyl
axis. There is evidence that compliance with regular medication can be
badly deficient. To assess how serious the problem might be in routin
e migraine management, we undertook a covert observational 2-month sur
vey in a specialist headache clinic using objective measures of compli
ance. Subjects were 38 patients needing prophylaxis with medication pr
escribed once (ed), twice (bd), or three times daily (tds). Medication
was dispensed, unknown to them, in Medication Event Monitoring System
s (MEMS) to record openings in real time. Number, timing, and pattern
of actual openings were compared with what was expected. Compliance ra
tes averaged 66%, although returned pill counts indicated 91%. A subst
antial and significant difference was shown between od and bd or tds r
egimens. Measures of dosing interval-used-on-schedule rate and therape
utic coverage-averaged between 44% and 71%. Once-daily treatment was a
ssociated with a used-on-schedule rate more than double those of multi
ple daily dosing, but still only 66%. We conclude that routine use of
drug prophylaxis in migraine may be so seriously undermined by poor co
mpliance that it has little chance of efficacy. Returned-pill counting
is inadequate for compliance assessment.