An enthusiast, or person who has an obsession with, or extreme knowledge of, something.
A drug addict.
A person who is extremely abnormal in appearance due to a severe medical condition (originally, a freak of nature); later extended to meaning a person who is extremely abnormal in social behavior, sexual orientation, gender identity, and/or business practices; an oddball, especially in physiology (e.g., "circus freak"); a unique person, originally in a displeasing or alienating way.
A person whose physique has grown far beyond the normal limits of muscular development; often a bodybuilder weighing more than 260 pounds (117.934 kilos).
A very sexually perverse individual.
A man, particularly a bold, strong, vigorous man.
A fellow; a petulant young man.
A hippie.
Strange, weird, unexpected.
To react extremely or irrationally, usually under distress or discomposure.
To be placed or place someone under the influence of a psychedelic drug, (especially) to experience reality withdrawal, or hallucinations (nightmarish), to behave irrational or unconventional due to drug use.
That said to be possessed by someone who is obsessed with something or only able to think of one thing.