To use/abuse or pleasure oneself with drugs. Usually referring to narcotics or rather hard drugs such as opiates (heroin, morphine oxycodone, methadone, demorol, ect..) or the stronger stimulants such as cocaine, methamphetime or other amphetamine like compounds. And also usually doing so in high excess/abuse.
person a:Man, that cat used to be cool but went over the edge with chemical masterbation
person b: what do you mean?
person a: he went off the deep end shootin coke.
person b: oh yeah your right, he jacked some money from me the other day.