Exercise has been shown to be effective in controlling attention deficit and hyperactivity disorder symptoms, and carries only positive side effects.
Other benefits of exercise include a strengthening of cancer defenses (see Exercise & Breast Cancer and Is It the Diet, the Exercise, or Both?), an improvement in cognition (see Reversing Cognitive Decline), and a longer lifespan (see What Women Should Eat to Live Longer).
This reminds me of other safe, natural, side effect-free solutions (like tap water gargling) to prevent the common cold (see Can Gargling Prevent the Common Cold?), and drinking water to improve scholastic performance in kids (see Does a Drink of Water Make Children Smarter?). The fact that they are cost-free is both an advantage (they’re free!), and disadvantage (no corporate budget driving their promotion, so we never hear about this kind of research). If only corporations could find a way to stuff exercise into a pill bottle for their stockholders…
For additional context, check out my associated blog post: How to Treat ADHD without Drugs.