What symptom may indicate that a medicine affects your driving ability?

Slight drowsiness is a significant symptom that can indicate a medication's impact on driving ability. Many medications, particularly those prescribed for anxiety, depression, and some pain relief, can induce drowsiness as a side effect. This state can impair concentration, reaction times, and overall alertness, which are critical for safe driving.

In contrast, increased focus, clear vision, and rapid heartbeat are not commonly associated with the impairments that affect driving. Increased focus is generally a desirable outcome, suggesting heightened awareness rather than a detriment. Clear vision would positively impact driving and is not a symptom of impairment. A rapid heartbeat can occur due to various reasons, including anxiety or certain medications, but it doesn't directly suggest drowsiness or a reduced capacity to drive safely. Thus, slight drowsiness remains the most pertinent symptom here regarding driving ability.