The body gets used to functioning with the drug present. Heavy and frequent use of cannabis can cause physical dependence. People can become psychologically dependent on any drug, including cannabis. This means that using cannabis becomes far more important than other activities in their life. The person craves the drug and will find it very difficult to stop using it.
People can develop a mild tolerance to cannabis.
This means they need to take more and more to get the same effect. It is unsafe to drive after using cannabis. Cannabis reduces concentration and co-ordination, impairs judgement and causes drowsiness. It is always dangerous to combine drugs. It is widely believed that using cannabis leads people on to other illegal drugs.