I have a granddaughter, now 16, that is ADHD. When elementary age, she was more ADD, impulsive but not hyperactive. Once puberty kicked in, she got more agressive and moody. Like puberty wasn't enough!
He sounds a bit more than ADD, more like ADHD. If his medication is the correct dose, I would concentrate on his diet. Cut out additives as much as possible; make sure sugar, lactose, and other things like dye are not triggers. He needs lots of exercise, and try to focus on his strengths. Observe what kinds of situations increase his symptoms and try to work on those. If he is not homeschooled, how do the schools deal with him? If they help, find out what methods they are using. If not, do the opposite :-) You are right about patience; nothing about this is easy.
As a grandparent, you can love him, be firm and consistent, help him to take responsibility for his actions. Encourage him, be patient with him. If others in the family come down on him, help him to understand what their issue is. And let the adults know that you expect them to help the kid, not just holler at him. God gave him to your family for a reason and they need to be a part of the solution, not an aggravation. As for the hurt, he is going to have to learn to control himself as much as possible. That, grandma, is a gift you can give him.