Lennon denied that the song had anything to do with drugs.
IMO, the following lyrics in the song makes it clear that it's about drugs. "I need a fix cause I'm going down Down to the abyss that I've left up town I need a fix cause I'm going down"
The audience can always read anything they want into a song. Lennon denies that the song was about drugs.
"Happiness Is A Warm Gun was another one which was banned on the radio - they said it was about shooting up drugs. But they were advertising guns and I thought it was so crazy that I made a song out of it. It wasn't about 'H' at all."
Here's the magazine cover.
A lot has been read into this song but most of the lyrics and images were bits and pieces of things that were heard in conversations or read about in the papers. Lennon put all those pieces together in a bit of a collage and voila!
"She's well acquainted with the touch of a velvet hand" -- Refers to a woman who's husband was into fetishes and used a moleskin glove
"The man in the crowd with muticolored mirrors"-- about a soccer fan who put mirrors on his shoes to see up women's skirts
"While his hands are busy working overtime" --about a man who used false hands as a shoplifting technique
"A soap impression...donated to the National Trust" -- about people defecating on public land owned by the National Trust.
"Mother Supeior" -- a term of endearment John used for Yoko.
This guy got his guns via a neighbor who purchased them for him. Although this guy was clearly a psychopath, he fooled everyone he came across in prison for 17 years, including the parole board. He was the model prisoner. I can imagine he also fooled the neighbor, a young girl who didn't know any better. All the time, he was plotting his plan to kill as many people as possible.