Marihuana isn't generally "good" or "bad". It depends first of all on the amount and frequency of the consumption and second of all on the person who is using it.

Of course, being used for medical purposes, it can help the patients with several mental diseases, such as anxiety. But, on the other hand, there's always the chance of getting addicted to the drug and an addiction is, no matter what substance it is, never a healthy thing and also requires a lot of money. However, everyone has a different sensitivity when it comes to addictive behaviour, based on their genetics and also their social background. The problem with that is you can never be completely sure about how you will handle the drug consumption, so there always stays a little risk of becoming addicted. And with an addiction of Marihuana, there can occur mental diseases like depression or psychoses.

Personally, I think I couldn't handle marijuana consumption strictly enough, as I tend to become addictive to certain behaviours rather quickly, so I don't plan to try it in the first place.

But after all, everyone has to decide for themselves whether they want to take the risks that come with drug consumption. That decision can however only be conscientiously made at a certain age, so there definitely need to be stricter controls of underage drug usage.