What drug, when taken with Seconal, will lead to a potentiation effect?

The correct answer is alcohol, which when taken with Seconal, can lead to a potentiation effect. Seconal is a barbiturate that depresses the central nervous system, and the combination of alcohol, another central nervous system depressant, can enhance the sedative effects of both substances. This results in an increased level of drowsiness, respiratory depression, and potentially dangerous side effects that can be life-threatening. The synergistic effect between the two substances heightens their individual effects, making the user significantly more sedated than if either substance were taken alone.

In contrast, substances like caffeine act as stimulants, which would counteract the depressant effects of Seconal rather than potentiating them. Nicotine, while it has some mild stimulant effects, does not significantly enhance the depressant effects of Seconal in the same manner as alcohol. Heroin, also a depressant similar to Seconal, could potentially cause dangerous effects, but in the context of this question, alcohol is more widely recognized for its pronounced synergistic effects with barbiturates.