Heroin.
Cocaine
Speed is another name for amphetamines, not for cocaine.
speed keeps you high for hours, cocaine doesn't last long. so in my point of view I'd have to say that speed is better.
The experiment produced mixed results, with some participants showing improvement while others did not.
Well yes and no, i would assume you mean dangerous substances like talcum powder or glass or something like that but it is simply an urban myth that cocaine is mixed with substances like this after all its not in the dealers intentions to kill someone. But then cocaine its self is a dangerous substance and is often mixed with similar, cheaper analogue of cocaine. These could be research chemicals which can potentially be lethal.
Speed or Cocaine
The drug known as Ecstasy is called MDMA, but most Ecstasy pills are cut with (mixed with) different drugs, usually heroin, cocaine, ketamine (Special K), or speed (amphetamines or methamphetamines).
On cocaine they can run 100mph
Many people i know are dying from it who use cocaine, it is mixed with phenacetin a banned cancer causing painkiller and people are taking more of it to get a hit as it gets mixed more yes definitely the word needs to be spread.
It's a name for a combination of drugs. It generally consists of heroin and cocaine mixed together in a syringe. Then shot into the users veins for what becomes the most intense and deadliest drug combos known to exist.
Not that I'm aware of, but colchicine can kill you.