Don't put the pussy on a pedastool, I mean the weed on a weed-a-stool. Weed, that ain't a big deal, people usually don't freak out on weed. I wouldn't worry too much, its just weed. If you wanted to introduce him to acid, or PCP, then that'd be completely different.

Just keep an eye on him, he should be fine. Maybe let him smoke alone his first time and kinda babysit him till hes used to it.