I don't think for any song there is a right or wrong answer, unless it comes straight from the songwriter.
But personally, I think, based on the lyrics "Under your covers more torture than pleasure" and "I'll break you my habit" that it's about a girl, but not a girl who changed his life for the better. I think maybe it's a girl who he was really into and then she got hooked on drugs and tried to get him on it too, and the "sense I never knew I had" was how he felt when he was on Heroine.
I think that the song is, like SheepShirts said, supposed to be both about the drugs and the girl, hence "My Heroine." But since he talks like he's talking to a person and talks about "the drugs begin to peak" that it is most definitely about both.
I don't think for any song there is a right or wrong answer, unless it comes straight from the songwriter.
But personally, I think, based on the lyrics "Under your covers more torture than pleasure" and "I'll break you my habit" that it's about a girl, but not a girl who changed his life for the better. I think maybe it's a girl who he was really into and then she got hooked on drugs and tried to get him on it too, and the "sense I never knew I had" was how he felt when he was on Heroine.
I think that the song is, like SheepShirts said, supposed to be both about the drugs and the girl, hence "My Heroine." But since he talks like he's talking to a person and talks about "the drugs begin to peak" that it is most definitely about both.