Does Therapeutic-Dose Lisdexamfetamine Lower the Seizure Threshold?
The proposition that stimulants lower the convulsive threshold has circulated in prescribing labels, clinical folklore, and specialist practice for decades. This appraisal asks whether it survives contact with the modern evidence base as applied to lisdexamfetamine (LDX) at therapeutic oral doses. It does not. Three large studies using orthogonal designs converge: a within-individual analysis of 801,838 patients with ADHD found odds ratios of 0.71 for seizure events during medicated months among patients both with (95% CI 0.60–0.85) and without (0.62–0.82) a prior seizure history; a matched Medicaid cohort of 18,166 stimulant users against 54,197 non-users, all children with epilepsy, found a hazard ratio of 0.95 (0.83–1.09); and a Swedish register study of 21,557 individuals with a seizure history found no increase following ADHD-medication initiation. Every adequately powered estimate lies at or below the null. None indicates harm. The warning's provenance has been independently traced to preclinical animal work and stimulant-overdose case reports rather than therapeutic-dose observation, and the U.S. Food and Drug Administration has since removed the seizure entry from the Warnings and Precautions section of the LDX label, retaining it only under Overdosage. Two qualifications are load-bearing and are frequently dropped in secondary summaries. First, the evidence is settled at the amphetamine-class level: LDX was inside the named exposure set of the largest study but has never been estimated as its own stratum, and no molecule-specific seizure estimate exists in the literature. Second, the finding is scoped to a defined exposure envelope — oral, intact prodrug, renally adjusted dose, and epilepsy controlled at initiation. We argue that the operationally correct framing is not a dose threshold but an exposure envelope, since renal impairment, urinary alkalinization, and CYP2D6 inhibition can each produce supratherapeutic exposure at a nominally therapeutic milligram count. We conclude with an explicit map of where the negative finding holds, where it thins, and where no data exist at all — a distinction the secondary literature routinely collapses. Keywords — `lisdexamfetamine` `seizure threshold` `ADHD pharmacotherapy` `epilepsy comorbidity` `within-individual design` `pharmacovigilance` `evidence appraisal`