Here’s a basic rundown of what to know about using heroin, including how long it stays in your system, side effects, and signs of an overdose. While not everyone who takes legal painkillers or recreational substances becomes addicted, some people won’t be able to stop taking them. People who overdose on heroin may seem like they’re asleep and snoring. If you’re not sure what’s happening to your friend or family member, try to wake them up to check if they’re OK. When people “cut” heroin, these extra substances can get into the bloodstream and block blood vessels.