Final answer:
Combining a sedative-hypnotic with amitriptyline (Elavil) can result in additive CNS depression due to their synergistic effects on inhibitory neurotransmitters in the brain.
Step-by-step explanation:
When it comes to the central nervous system (CNS) depressants, co-administration with other drugs that have CNS depressant activity can lead to additive CNS depression. Among the options provided, combining a sedative-hypnotic with amitriptyline (Elavil), an antidepressant with anxiolytic and sedative properties, would be most likely to result in additive CNS depression. This occurs because both sedative-hypnotics and amitriptyline enhance the inhibitory effects of neurotransmitters that slow down brain activity, which could lead to enhanced sedation, respiratory depression, and potentially dangerous side effects.
Other substances listed, such as methylphenidate (Ritalin), cocaine, and amphetamine (Adderall), are CNS stimulants and generally increase brain activity. However, they do not commonly produce additive CNS depressant effects when taken with sedative-hypnotics.