Its a lot like alcohol. It affects the brain. Not in any way that would be deemed physically harmful but it exaggerates underlying medical conditions revolving around personality disorders and mental disorders.
Its the type of drug that requires sincere caution but is mostly harmless. Lulling a lot of people into a false sense of security.
I think it should be legalized and regulated by the government very carefully in the same way that alcohol is. But, again, you have to bear in mind how very, very young humanity is in the front of legalization of drugs.