It's from Sci Fi Channel's late, great Invisible Man series. A thief, Darien Fawkes, is sent to prison for life under California's three strikes law. His brother Kevin is a scientist working on a top secret project, and he pulls some strings to get Darien's sentence commuted in exchange for Darien's being the guinea pig for this gland that can secrete a substance called Quicksilver, which bends light. Darien agrees and the gland is implanted into his head, but a terrorist who infiltrated Kevin's project engineered a genetic mutation in the gland so that it would keep pumping Quicksilver into the bloodstream. If too much Quicksilver builds up, it turns Darien into a totally uninhibited lunatic. So, after Kevin is killed by the same terrorist, Darien goes on the run until he's contacted by a government unit known simply as "the Agency." They offer him a counteragent that can flush the Quicksilver out of his system and keep him sane, and in return they want him to work for them and use the gland in spy missions.
The premise sounds a lot more serious and sinister than it really is, though. The most entertaining aspect about it was Darien and his Agency partner Hobbes' (a chronically paranoid pill-popper who keeps a book called "Lithium and You" in his car) weird, random banter.
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