Vitamin D as a Therapeutic Adjunct in the Stimulant Treatment of ADHD

Inclusion Criteria: * Age 18-50 years * Voluntary, written, informed consent * Physically healthy by medical history, physical, neurological, ECG, and laboratory examinations * For females, non-lactating, with a negative serum or urine pregnancy test * Lab results without clinically relevant findings (e.g. renal function, electrolytes, and vitamin D levels) * English speaking Exclusion Criteria: * Medical contraindication to Dexedrine administration (e.g., history of cardiac problems, seizures, glaucoma, hypertension, hyperthyroidism, etc.) * Medical contraindication to calcitriol administration (e.g., history of hypersensitivity to calcitriol or any component of the formulation, hypercalcemia or vitamin D toxicity) * History of substance dependence (e.g., alcohol, opiates, sedative hypnotics), except for nicotine * A primary major DSM-5 psychiatric disorder (e.g., schizophrenia, bipolar disorder, major depression, etc.) as determined by the Structured Clinical Interview for DSM-5 (SCID) * A history of significant medical (e.g., cardiovascular, diabetic/metabolic) or neurological (e.g., cerebrovascular accidents, seizure, traumatic brain injury) illness * Positive answers on the cardiac history questionnaire that may place the subject at higher risk, as determined by an internal medicine specialist or cardiologist's review of both the questionnaire responses and screening ECG * Current use of psychotropic and/or potentially psychoactive prescription medications * For femal…