After taking first-generation antihistamines, how long should a driver wait before operating a Commercial Motor Vehicle (CMV)?

First-generation antihistamines, such as diphenhydramine and chlorpheniramine, can cause significant drowsiness and impair cognitive and motor functions. These effects can last longer than the medication's peak effects, meaning that even after the last dose is taken, drivers may still be impaired.

The recommendation for a wait time of 12 hours after taking these antihistamines before operating a Commercial Motor Vehicle (CMV) is based on the understanding that this time frame allows the majority of sedative effects to diminish. It is critical for the safety of the driver and the public that those operating CMVs are fully alert and capable of responding to all driving conditions.

In certain circumstances, while some may suggest shorter time frames, it is vital to err on the side of caution given the potential risks involved. Various regulations emphasize that the driver should be completely free of any impairing effects before engaging in activities that require full attention and quick reflexes, such as driving a CMV. This ensures compliance with safety standards and regulations while minimizing the risk of accidents due to drowsiness.