Orexins/hypocretins (OX) and melanin-concentrating hormone (MCH) neurons located in the lateral hypothalamus seem to modulate different stages of the sleep–wake cycle. OX are necessary for wakefulness and MCH appears to regulate rapid eye movement sleep (REMS). Likewise, endocannabinoids, the endogenous ligands for cannabinoid receptors 1 and 2 (CB1R, CB2R), also modulate REMS in rats. Moreover, it has been shown that the activation of the CB1R in the lateral hypothalamus of rats excites MCH neurons while inhibiting OX neurons in in vitro preparations. Hence, we assessed the effects of 2-arachidonoylglicerol (2-AG, an endocannabinoid) in the lateral hypothalamus on the sleep–wake cycle of rats. We also utilized the CB1R inverse agonist AM251 to further support the involvement of this receptor, and we performed double immunofluorescence experiments to detect c-Fos, as a marker of neural activation, in OX and in MCH neurons to determine which neurons were activated. Our results indicate that 2-AG increases REMS through CB1R activation, and increases c-Fos expression in MCH neurons. These results suggest that endocannabinoid activation of the CB1R in the lateral hypothalamus, which activates MCH neurons, is one mechanism by which REMS is triggered.