- Unable to undergo an 18F-DOPA PET scan (e.g. Parkinson's disease, taking anti-dopaminergic, or dopamine agonist medication or less than 6 half-lives from discontinuance of dopamine agonists; NOTE: other potentially interfering drugs: amoxapine, amphetamine, benztropine, buproprion, buspirone, cocaine, mazindol, methamphetamine, methylphenidate, norephedrine, phentermine, phenylpropanolamine, selegiline, paroxetine, citalopram, and sertraline; if a patient is on any of these drugs, list which ones on the on-study form