I'm surprised the meds aren't helping, at least a little.
He is still very little, though, and with ADHD, his impulse control is more like a 3 year olds, so remember that. Put dangerous or breakable stuff away. And practice replacement. Give him stuff that he can hold and touch. Tell him what he can touch, rather than just what he can't touch. Or when/how he can touch it, rather than simply no. You need to find the appropriate "yes's". (Like if he touches a stranger's hair, you can say something like "You can touch Mommy's hair if you want to touch hair. " or "If you want to touch hair, pet your Teddy Bear's hair. See how soft it is!" Some kids have things like velcro under their desk so that they can touch the velcro if they need to touch something with some texture. Many ADHD kids have fidgets or squeezy balls that they can hold or squeeze during class.

Use behavioral methods like the 1,2,3 Magic method. Also praise him when you know he wants to touch something but doesn't. If it's a dangerous item, like medicine, put it under lock and key.

He grabs everything, it's driving me mad. I can't stop him, he lacks the ability to regulate himself. Does his improve? Meds really arent helping with this.