junkie:
(plural: ‘junkies‘; also ‘junky’ with plural form ‘junkies‘ — for the righty pronunciation, please click here)

a typical junkie injecting himself with heroin
a person who takes junk as a habit, i.e. a person who habitually injects illegal drugs, especially ‘heroin’, into him/herself (‘junk’, in this context, = an illegal drug that is very harmful, especially ‘heroin‘);
a drug addict;
a person who has too much interest in something, such as sport, art, etc.,

sports junkies painted all over to show their support to their favourite team at a football match
Matilda started using mild drugs to impress her peers and boyfriends but has now become a seasoned junkie who needs rehabilitation.
As more and more drugs, especially heroine, are very easily available, the number of junkies is on the rise, and using drugs in open public places has become a serious issue.
There are different kinds of junkies, apart from the drug junkies, with the basic meaning ‘too much interest in something’: food junkies, theatre junkies, sports junkies, music junkies, FaceBook junkies, political junkies, and so on.
Whatever be the nature of the junkies — drugs, music, sports, the internet, the police have tough time keeping those junkies under control because, though each type is different from the other, the basic problem of disrupting the peace and decency of the neighbourhoods stays the same!
