Heroin is a bad mixer and will only make the chances of unconsciousness, vomiting and choking greater. Only 21% of fatal overdoses in a recent Australian survey came about through using heroin on its own.

Please note: there have been very few scientific studies into the effects of combining psychoactive drugs. The information presented here is anecdotal. It is based on the subjective reports of experienced users. Different people will respond differently to different drugs and drug combination. Know your body.

alcohol don't; alcohol and heroin both depress the central nervous system. The combination has proven fatal

amphetamines mixing uppers and downers is not good; speed's stimulant effects may mask the opiate effects of heroin and make overdoses more likely

cocaine don't; mixing the two (known as a 'speedball') is especially dangerous; the two drugs potentiate each other, increasingly their effectiveness twofold. The cocaine acts as a powerful stimulant raising the heartbeat but its effects wear off quickers than heroin which in turn slows the heart. As a result, the heart can lose rhythm entirely. John Belushi and River Pheonix both died after taking speedballs.

ecstasy MDMA's effects may mask opiate effects of heroin and make overdose easier

ghb don't; GHB is a liquid sedative anaesthetic; mixing it with heroin could fatally depress the central nervous system

ketamine doesn't work

LSD psychedelic drugs mess with the effects of opiates, making them unpredictable and usually unpleasant

mushrooms as above

tobacco no harmful effects