In almost all instances that would not be correct.
Propanalol, just as the classic example of a beta blocker, might slow metabolism a little, but only in some people, and the mechanisms is not known as to how it does this. In addition, a slightly slower metabolism in general does not indicate any direct effect on alcohol degradation, in fact, it might speed up independently.
The direct interaction of the two drugs is to lower blood pressure
, but not to affect the catabolism of propanalol.
So, you can not argue that your alcohol level would not reflect the amount you actually drank because you are on propanalol. There are too many factors involved.
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