Disclosed is a composition that includes a tetrahydrobiopterin in a controlled-release pharmaceutical preparation. Also disclosed is a method of treating a patient with phenylketonuria that includes administering, to the patient, a composition that contains tetrahydrobiopterin in a controlled-release pharmaceutical preparation. Also disclosed is a method of treating a patient with ADHD that includes administering a tetrahydropterin to the patient. Compositions for the treatment of ADHD are also described.
