Context Many health plans have instituted more cost sharing to discourage use
of more expensive pharmaceuticals and to reduce drug spending.
Objective To determine how changes in cost sharing affect use of the most commonly
used drug classes among the privately insured and the chronically ill.
Design, Setting, and Participants Retrospective US study conducted from 1997 to 2000, examining linked
pharmacy claims data with health plan benefit designs from 30 employers and
52 health plans. Participants were 528 969 privately insured beneficiaries
aged 18 to 64 years and enrolled from 1 to 4 years (960 791 person-years).
Main Outcome Measure Relative change in drug days supplied (per member, per year) when co-payments
doubled in a prototypical drug benefit plan.
Results Doubling co-payments was associated with reductions in use of 8 therapeutic
classes. The largest decreases occurred for nonsteroidal anti-inflammatory
drugs (NSAIDs) (45%) and antihistamines (44%). Reductions in overall days
supplied of antihyperlipidemics (34%), antiulcerants (33%), antiasthmatics
(32%), antihypertensives (26%), antidepressants (26%), and antidiabetics (25%)
were also observed. Among patients diagnosed as having a chronic illness and
receiving ongoing care, use was less responsive to co-payment changes. Use
of antidepressants by depressed patients declined by 8%; use of antihypertensives
by hypertensive patients decreased by 10%. Larger reductions were observed
for arthritis patients taking NSAIDs (27%) and allergy patients taking antihistamines
(31%). Patients with diabetes reduced their use of antidiabetes drugs by 23%.
Conclusions The use of medications such as antihistamines and NSAIDs, which are
taken intermittently to treat symptoms, was sensitive to co-payment changes.
Other medications—antihypertensive, antiasthmatic, antidepressant, antihyperlipidemic,
antiulcerant, and antidiabetic agents—also demonstrated significant
price responsiveness. The reduction in use of medications for individuals
in ongoing care was more modest. Still, significant increases in co-payments
raise concern about adverse health consequences because of the large price
effects, especially among diabetic patients.