Answer:
To [sibiling's name]
Hi! Remember when you were interested in drugs and wanted to try them? I just wanted to remind you that drugs are not good for you in any way. I do understand your curiosity about drugs. I also am curious! Because of the fact we never tried them before and if people around you keep saying that "Oh, you should not use drugs!" it's likely for you to be more interested and curious about them.
Drugs are not good for you. They are disadvantages, and they have negative impacts on you. Recently, in South Korea, there were two individuals that convinced students to drink drugs. They persuaded them that if they drank this they would be able to focus more. But it was not the case. It was just a bunch of drugs. This only would make you stressed and go through numerous health problems, which is why it would be a negative impact on you.
I hope you acknowledge the impacts and circumstances you receive when you try drugs. Drugs do not have any benefit! Remind yourself about that! They are seriously dangerous liquid resources we have in our society. Rember to stay safe!
From & with love [your name]