As with smoking, there are a number of negative side effects when consuming caffeine, especially in high quantities. Insomnia, nervousness, restlessness, irritability, an upset stomach, a fast heartbeat and even muscle tremors may occur. Besides that it can be quite addictive. In many respects it seems quite akin to smoking.
Yet, as far as I can tell, there have been no rulings on caffeine or caffeinated beverages. Is it simply that scholars have not investigated it yet?