EXCLUSIVE — House Republicans are escalating their investigation into the Drug Enforcement Administration’s handling of the shortage of stimulant medications used to treat attention-deficit/hyperactivity disorder, or ADHD, hinting at a subpoena should the agency not respond.

On Friday, House Oversight Committee Chairman James Comer (R-KY) and Healthcare and Financial Services Subcommittee Chairwoman Lisa McClain (R-MI) sent a letter obtained by the Washington Examiner to DEA Administrator Anne Milgram requesting information regarding the agency’s lack of action to increase the manufacturing limit on amphetamines necessary to treat ADHD, including Adderall, Vyvanse, Concerta, and Ritalin.