Impact of a household-level deductible on prescription drug use among lower-income adults: a quasi-experimental study.

backgroundSeveral Canadian public drug plans have income-based deductibles, but we have limited data on their impact, particularly for vulnerable populations. Therefore, we studied the impact of deductibles in British Columbia's Fair PharmaCare program on drug use among lower-income adults.

methodsWe used a quasi-experimental regression discontinuity design to study the impact of BC rules that impose no deductible before receiving public coverage on households with incomes less than $15 000, a deductible of 2% of household income on those with incomes between $15 000 and $30 000, and a deductible of 3% of household income on those with incomes above $30 000. We studied the impact of these thresholds on public and total drug expenditures between 2003 and 2015 using 24 million person-years of data.

resultsBoth thresholds decreased the proportion of beneficiaries receiving benefits, by 0.33 (95% confidence interval [CI] -0.34 to -0.30) and 0.05 (95% CI -0.064 to -0.032) respectively. There were also substantial reductions in the extent of public drug plan expenditures ($59.94 [95% CI -74.74 to -45.14] and $26.12 [95% CI -39.78 to -12.46], respectively). The change at the $15 000 threshold reduced patient drug expenditures by $26.00 (95% CI -45.48 to -6.51), or 7.2%. In contrast, we found no statistically significant change in total expenditures when households moved from a deductible of 2% to 3% at the $30 000 threshold.

interpretationIncome-based deductibles considerably affected the extent of public subsidy for prescription drugs. For lower-income households making around $15 000, the deductible led to a reduction of 7.2% in overall drug use and costs. Although deductibles are a useful tool to limit public expenditures, policy-makers should be cautious in their use among vulnerable populations.