Used in the novel A Trivial High to describe a person who'll stop at nothing to get high.
"X, H, K... She'll do the entire alphabet. A true druggernaut." -A Trivial High
Someone who does copious ammounts of different drugs.
Mike: Shit did you hear about Tim? He did lsd, ecstasy, ketamine, cocaine, and 2c-e at that party last night, he ended up puking on the stereo.
Ryan: What a druggernaut.