Final answer:
The half-life of caffeine is shorter in smokers because nicotine stimulates the liver to produce more cytochrome P450 enzymes, which rapidly metabolize caffeine.
Step-by-step explanation:
The half-life of caffeine is shorter in smokers due to the increased metabolism of caffeine by the liver enzymes that are induced by substances in tobacco smoke, primarily nicotine. Nicotine stimulates the liver to produce more cytochrome P450 enzymes, which are responsible for metabolizing many substances, including caffeine. Thus, when a smoker consumes caffeine, it is broken down more rapidly, leading to a shorter half-life. These enzymes are particularly efficient, causing drugs and other substances, such as antidepressants, anticonvulsants, and even the caffeine in coffee or other sources, to be metabolized more quickly, making them less effective or reducing their presence in the body sooner.