15 things you should know about caffeine / coffee. "Caffeine is a stimulant which works by increasing your dopamine level, which makes you happier. It also blocks your adenosine receptors, which stops you from getting drowsy. 5mg of caffeine per kg of body weight can improve endurance by reducing glucose burning and increasing fat burning. So it does benefits athletes. However like many stimulants, it can cause physical dependence." They forgot it can trigger heart arrhythmias.