In addition to the thermogenic effect already discussed, caffeine, as the main active substance in guarana, also performs a function at the level of the b-adrenergic (read beta adrenergic) and α-2-adrenergic receptors. The latter, which we have already encountered, when active have the function of promoting adipocyte filling, while the former have the opposite effect. Now, caffeine, by reducing the density of the α-2-adrenergic and increasing that of the β-adrenergics can hinder the process of adipocyte filling. It should be noted that the effects of guarana on α-2-adrenergic and β-adrenergic receptors only take place if one undergoes some kind of training regime. It therefore does not take place in sedentary people. Regarding the side effects of guarana, the form in which it is commercially available and the dosage, please refer to the section on thermogenics dedicated to this supplement.