Adenosine is a nucleoside composed of Adenine and β-D Ribose (sugar). It is part of many important body-own substances (e.g. ATP, coenzyme A, NADH, RNA). Adenosine block the stimulating neurotransmitters (e.g. acetylcholine, dopamine, norepinephrine). This causes dilatation (widening of blood vessels), resulting in a lowering of blood pressure and a decrease in heart rate. It also acts on the A1 Adenosine receptors in the hypothalamus. This is where GABA (ɣ-Aminobutyric acid) is released, promoting sleep.