None of the herbal things work, they can be dangerous, and you really should not be trying these for a medical condition without the suggestion of your doctor. Many untreated people with ADHD use caffine and niccotine to self medicate. You could try caffine, but you will do much better with real medical care and support.
More questions for you: what does his play therapist or cognative behavioral therapist say about the aggression and what are you doing for it in therapy? What does his OT say about chewing in clothing? Are you doing the sensory homework, like brushing, carrying heavy objects, etc? If you do not know what I am talking about, then you need to back track and try a complete standard treatment program, which will include several hours per week with therapists and daily homework for you and your son to do at to help him. If you do not have a doctor who can see you as often as is needed to adjust the medication so that he can access his many weekly therapies and daily homework, then you should find a new doctor who can. ADHD is not a DIY condition, it really does take expert medical care and very frequent adjustments to get the full treatment right. If he is just taking pills, he is not getting good care for his condition.
A board certified child psychiatrist will be the best doctor for him, and our experience is that if you find an idependent psychiatrist (one who is not on any insurance plan) they will be able to see him as often as his condition requires it. It may be expensive, but it is worth it if your son has a difficult case to treat. It is possible to find the right combo and start benefiting from all the therapy he needs.