What does "the substance issues" mean in this context?

Dear All,

I read a book and am not sure what is meant by "substance issues" in the context below:

"My life in
America is riddled with things I’d rather Mum didn’t know about.
I’ve literally had nightmares over whether she’s seen the tacky videos
on YouTube that people have occasionally posted of me performing
in some dead-end gig. But that’s just the tip of the iceberg. There’s
the fractured relationships, the substance issues, the frequent lack
of a permanent address’ that sums up my lifestyle. " (excerpt from Lauren Westwood "My mother's silence")

Does it mean "drug addiction" or searching for some "meaning of life"?

Thanks!