The drug
Drugs are not all the same. Different drugs have different dangers associated with them.
Some drugs (such as alcohol, heroin and tranquillisers) have a sedative effect which slow down the way the body and brain function. They can have a numbing effect that produces drowsiness if a lot is taken. Other drugs (such as amphetamine, cocaine, crack and ecstasy) have a stimulant effect giving a rush of energy and making people more alert. A third group of drugs (such as LSD and magic mushrooms and to a lesser extent cannabis and ecstasy) have a hallucinogenic effect. This means they tend to alter the way the user feels, sees, hears, tastes or smells.
Sedative drugs like alcohol and heroin can lead to fatal overdose if a lot is taken. They can also affect co-ordination making accidents more likely. Use of sedatives can also lead to physical dependence and withdrawal symptoms while others drugs like cannabis cannot.
Stimulant drugs can produce anxiety or panic attacks particularly if taken in large quantities. They can also be particularly dangerous for people who have heart or blood pressure problems.
Hallucinogenic drugs sometimes produce very disturbing experiences and may lead to erratic or dangerous behaviour by the user, especially if they are already unstable. And of course some drugs are legal to use and others are not. Being arrested and getting a conviction can lead to all sorts of problems.