An individual who is overzealous, over involved, or too on to some shit nobody else cares about or wants to be concerned with at the time. Much like how a pill that you consume has the capability to over influence of your mind/mental state.
"It's been over 2 months and Dylan still won't shut up about The Wire. What a pill."
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"Quit being a pill, Will, we all f***ing know Lil Nas X slaps okay!"