It is unlikely that governments will ever be able to completely stop people from using marijuana.  Nothing that they have done so far seems to have worked.

In theory, governments should be able to stop marijuana use with harsh penalties.  However, it is not clear that any government is willing to hand out punishments harsh enough to prevent people from using marijuana.  For example, it seems unlikely that any country will be willing to give a person 10 years in prison for simply smoking marijuana.

Governments might also be able to stop people through education.  If the government shows people that smoking marijuana is very bad for them, they should stop.  However, people do not really act in this way.  We do all sorts of things that are not good for us because we like their good aspects more than we fear their bad effects.

What this means is that governments can surely not completely end marijuana use.  They can hope to reduce it through harsh penalties on major dealers and through education, but they cannot completely prevent it.