Final answer:
Cold medicine taken by a driver who has been drinking can increase drowsiness and impair driving ability.
Step-by-step explanation:
The effect that a cold medicine might have on a driver who has been drinking is that it may increase drowsiness and impair driving ability.
Both alcohol and cold medicine are known to cause drowsiness. When these substances are combined, they can have an additive effect on the central nervous system, leading to increased drowsiness and impaired motor skills.
It's important for individuals who have been drinking to avoid driving, regardless of whether they have also taken cold medicine, as impairment from alcohol alone can be dangerous and illegal.