Should I tell that my brother is doing drugs?

I don’t believe it will make a difference one way or the other. Teenagers will do as they please regardless of how their parents feel, it’s just the rebellious age. The Chemicals awash in your brain at that age when your going through puberty cause you to take more risks and do stupid things. The accidental death rate of teenagers is higher than that of children and adults. You think you know it all and will live forever, you become more competitive in nature trying to attract the opposite sex. If you rat him out he may get into trouble and quit or he may not, but you can be sure he will no longer trust you leaving you in no position to help him in the future. So it’s entirely up to you if it is worth it. I would suggest that if he is using hard man made drugs such as cocaine or heroine that you report it to your parents, but if it’s just pot which is impossible to overdose on then just let it slide. It’s more than likely that Murphy’s law will eventually catch up and he will get busted by the police which will more likely deter him and to cause him to quit using it than just your parents telling him “No” which would likely just make him want to use more. Some people just have to learn the hard way. Tough love is a tricky thing to calculate, but the choice is your to make, and there really isn’t a definitive wrong answer. It’s all in how you perceive it.