What drug can kill you?

If it can be consumed it can kill you, for the most part. If you're talking about illegal drugs which I assume is true, then marijuana won't hurt you, and neither will psychedelics like LSD and mushrooms. Ecstasy is safe if you treat it with respect and don't go overboard.

Then there are the ones that will kill you, the ones you probably think of, mostly pills. Prescription painkillers, opiates, like Oxycotton, Morphine, etc. can be dangerous if you go too far or mix with alcohol, and are addictive. Heroin also falls into that group. Then there are Benzodiazepines which you can't overdose on alone very easily, you'd need to take bottles of them to, but as soon as you mix with alcohol or a different benzo you're in for blackouts or death.

Then there's stimulants like the obvious one, meth, which is obviously dangerous and addictive if you smoke it or shoot it up. If you were to eat it though it wouldn't be very addictive or harmful. Also prescription stimulants like Ritalin, Focalin, and Adderall. These are pretty safe if taken orally, or even nasally, and though they aren't perfect the LD50 is pretty high, so you won't overdose easily.

Hope that helps