A patient exhibits euphoria, glassy red eyes, loud talking, dry mouth, excessive hunger, and sleepiness. What substance are they likely intoxicated with?

The symptoms described—euphoria, glassy red eyes, loud talking, dry mouth, excessive hunger, and sleepiness—are characteristic of marijuana intoxication.

Euphoria is a common effect of marijuana use, often accompanied by alterations in mood and perception. The glassy red eyes are a distinctive physical sign of marijuana use due to the dilation of blood vessels in the conjunctiva. Loud talking can stem from the disinhibitory effects of the substance, leading users to exhibit increased sociability and a reduction in social anxiety.

Additionally, dry mouth, often referred to as "cottonmouth," arises from the effects of cannabinoids on salivary gland function. Excessive hunger, commonly referred to as "the munchies," is a well-known effect of marijuana, as it can significantly enhance appetite. Sleepiness can occur as well, particularly if the user is consuming high-THC strains that are more sedative in nature.

Given all these aspects, the combination of symptoms strongly points to marijuana intoxication as the most fitting answer.