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Abuse of Medications That Theoretically Are Without Abuse Potential. Reeves RR et al. South Med J 2015 Mar;108:151-157.
Abstract
This review of noncontrolled prescription and over-the-counter drugs that can be and have been abused for non-medical or recreational purposes is rather sketchy and anecdotal (as the authors admit,) but nevertheless contains some useful information.
Classes of drugs discussed include:

Cold & Cough products: pseudoephedrine, ephedrine, oxymetazoline, dextromethorphan
Anticholinergics: diphenhydramine, benztropine, trihexyphenidyl (Artane)
Antipsychotics: quetiapine, olanzapine
Antidepressants: tricyclics, bupropion, fluoxetine, venlafaxine
Anitconvulsants: pregabalin, gabapentin
Muscle relaxants: carisoprodol, cyclobenaprine (Flexer…