“Cotton mouth” is longstanding cannabis slang for an extremely dry mouth, such as the kind you only get from a medicated effect. Cotton mouth is a common condition in cannabis consumers, bringing with it a difficulty in swallowing, a rise in oral acidity, and a sensation of unquenchable thirst no matter how much liquid you drink.
It is important to avoid sugary drinks while experiencing cotton mouth, because your oral defenses are down already and sugar at this point just promotes faster tooth decay. Stick to sugarless drinks or chewing sugerfree gum to counteract cotton mouth.
There is a consistent set of side effects of THC (the main active ingredient in cannabis) which includes cotton mouth, and also red, bloodshot eyes and an increased appetite. Some individuals are more prone to it than others. The effects of both cotton mouth and bloodshot eyes are caused by THC binding to some receptors in the endocannabinoid system, temporarily shutting down the regulatory systems the body has to manage mucus membranes.