The Mellanby Effect describes impairment being greater at a given BAC when BAC is increasing than when falling. Which option correctly states this?

• A. Impairment is greater at a given BAC when BAC is increasing than when BAC is falling
• B. Impairment is greater at a given BAC when BAC is decreasing than when rising
• C. Impairment is unrelated to the direction of BAC change
• D. Impairment is greater at a fixed time after drinking

Answer: (A)

The Mellanby Effect shows that impairment at a specific BAC depends on whether that BAC is rising or falling. When BAC is increasing, the brain is more sensitive to alcohol’s effects, so impairment is greater at that same BAC than it is later on when BAC is decreasing. As BAC climbs, acute tolerance hasn’t developed yet, leading to stronger impairment; once the level starts to fall, some acute tolerance has built up, and the same BAC produces less impairment. So the best statement is that impairment is greater at a given BAC when BAC is increasing than when falling.