A common classification of drugs into Hard drugs and Soft drugs. Some drugs cannot be clearly classified that way, they are at the intersection of both circles.
Certain kinds of drugs that act on the nervous system are sometimes loosely classified. Usually there are the following categories:
Hard drugs are drugs that lead to severe physical addiction. Many countries do not allow people to make, sell or use some of them, other than for medical purposes. Examples of such drugs are heroin, methamphetamine (meth), alcohol and nicotine. If it is legal to sell them, like with alcohol or nicotine, there are often taxes that need to be paid for them.
Soft drugs do not cause physical addiction. Examples of soft drugs are cannabis, mescaline, psilocybin and LSD. While they do not cause physical addiction, some of them may still lead to psychological dependency. Psychological dependency is a dependency of the mind. This means that people feel better when they have the drug. When they do not have the drug, they may be in a bad mood, for example.
Some drugs cannot be classified that way, as they have characteristics of both hard and soft drugs. Examples for such drugs are MDMA (known as Ecstasy), ketamine and caffeine.
In the Netherlands, there is a situation where the use of some "soft drugs" is tolerated.