Such as? From what I've seen it's no where near the effects of alcohol, but yes there are some small side effects that don't make it "100% safe" but the same thing goes with basically everything, including Tylenol.
Marijuan causes mania http://www.sciencedaily.com/releases/2015/02/150210160101.htm
It changes the structure of the brain http://www.sciencedaily.com/releases/2014/04/140415181156.htm
It causes permanent loss of memory http://www.sciencedaily.com/releases/2015/03/150312082906.htm
Marijuana is addictive http://www.sciencedaily.com/releases/2014/07/140716090846.htm
Marijuana can also increase impulsive behaviors which could trigger use of other drugs http://www.sciencedaily.com/releases/2014/07/140716090846.htm
That isn't a good enough reason to ban it.
Mania is a side effect to many prescription drugs. Not really a huge problem anyway.
Alcohol changes your brain structure even more so, should that be illegal also in your opinion?
It CAN cause permanent memory loss by users who use it daily... So back to the alcohol question.
Caffeine is addictive.
Again, alcohol does the same, but the true argument is so what? It's someone's personal choice to start using a worse drug, not the drug's fault. We don't blame alcohol for drunk drivers do we?
So like I said no it's not "100% safe." But nothing is. You can find problems with virtually everything.
"Alcohol changes your brain structure even more so, should that be illegal also in your opinion?" If you could feasibly keep alcohol illegal then yes I do think alcohol should be illegals. But guess what, we couldn't keep alcohol illegal longer than 15 years if we wanted to. Marijuana has been illegal for 45 years without the problems. If we wanted to keep marijuana illegal for 45 more years, we could.
There's so much money currently being spent on law enforcement to bust people who use marijuana all for what? The cartel is making bank off a law that isn't followed by many. And besides if marijuana was legalized, it would be more safe since it would not have a chance of being laced with something, and the taxes we could make from it would be well worth it.