We thank Drs Kaufman and Malone for raising questions about the implication of our study on the use of methylphenidate in Michigan. We did not intend to represent our findings as indicative of the lifelong prevalence of ADHD. Rather what we present is the point prevalence of the use of methylphenidate. Because our database was all prescriptions written for methylphenidate and did not include any information about diagnosis, we can only speculate about the relation of the use of this medication to the disorder of ADHD.
The authors' letter provides the opportunity to extend the discussion of the implications, as well as to clarify specific questions about our method. We did not observe the single-prescription phenomenon found in the study of Sherman and Hertzig.1 In fact, the majority of recipients in our study received 2 sets of prescriptions during the 60-day study period. The time frame for the point