A patient presents with slurred speech and mydriasis. What substance is most likely involved?

In this scenario, the combination of slurred speech and mydriasis (dilated pupils) points towards a substance that affects the central nervous system in a specific way. Slurred speech typically indicates an impairment in motor function or coordination, which can be associated with depressants like alcohol. Mydriasis occurs due to the stimulation of the sympathetic nervous system, and while various substances can cause this effect, it's important to consider the overall clinical picture.

Alcohol is a depressant that can lead to slurred speech due to its effects on cognitive and motor functioning. Mydriasis may occur in some cases but is more commonly noted with stimulants. However, when evaluating both symptoms with alcohol in mind—the impairments in speech and motor coordination, along with the potential for mild mydriasis in higher doses—alcohol remains a strong candidate.

Other substances like cocaine and MDMA may also cause mydriasis, but they typically lead to increased energy, euphoria, and potentially more ranges of abnormal vital signs rather than pronounced slurred speech. Heroin, being an opioid, would generally present with pinpoint pupils and would not commonly cause mydriasis. Thus, the combination of slurred speech and mydriasis,