Some hospitals and doctors are allowed to prescribe medicinal marijuana in some countries, but there aren’t hospitals that only do this. It’s use as a medicine is legal in some countries but not that many, they also don’t often prescribe weed, they give people tablets or vaporisers so that they don’t have to smoke, and it is often synthetic rather than naturally grown.
There are some cases where its use has been shown by scientists to be beneficial, and it can help reduce pain or things like involuntary muscle movement in patients with multiple sclerosis which can make their quality of life much better. And there is some very recent evidence that it could be used to fight breast cancer.
However these are very specific cases and the doses and type of drug used are very carefully controlled by the doctor in charge of the patient.
In some cases, smoking weed can be beneficial – for example for patients who are in constant pain may find some relief. I have never heard of it being prescribed in hospitals in the UK though, and as far as I know, it is still illegal. I know it is a controversial issue – some people claim that it is medicinal, and also not as bad for you as other drugs such as ecstasy, heroin etc. But long term use of it can lead to changes in a persons mental state – having impacts on concentration, motivation, depression and sex drive. It also increases chances of getting some sort of lung problem, similar to those who smoke normal cigarettes.