I also want to add that while it is important to find a way to discipline a child with a developmental disorder, it can be difficult to implement it. For instance, when my daughter (who has autism) was younger she could not handle time outs. She threw everything around her and pounded on her door. A child like this does not understand what you are trying to teach them during a melt down. Instead we showed her that there were direct consequences to tantrums. If she threw something she had to pick it up (even if we waited until she was calm), if she broke something we threw it away, etc. We didn't exactly punish her, but there were still repercussions. You really have to meet the child at their level and figure out how to connect to them. Even kids with disabilities need boundaries.
Talk to his doctor about ways to add fish oil to his diet. I buy it in liquid form and dump a little bit on my daughter's food. My daughter is 7 and has autism. I do not give her any sort of medication. She does take melatonin and fish oil supplements along with behavioral therapy. I'm all for no medication if possible!
And along with behavioral therapy seek advice on nutrition. An improper diet can worsen ADHD and a suitable one can modify it.
Glad to hear that you are not using meds at this age as the clinical guidelines recommend behavioral therapy first. I am kind of curious where you read about the meds being "hazards long term"? Haven't really seem much research on that. In fact, to some extent, the opposite might be true.
But anyway, here are two links which I think you will find helpful.
http://www.onhealth.com/tips_for_parenting_a_child_with_adhd/page3.htm
http://www.additudemag.com/channel/parenting-adhd-children/index.html
You might want to post over on the adhd forum where its members might have had more experience with this.
http://www.medhelp.org/forums/ADD---ADHD/show/175
Have you tried disciplining him? Timeouts work very well for a 4 year old.