In my limited knowledge, if a person who, relative to another person, weighs more, it takes longer and more alcohol consumption for the heavier person to reach a certain BAC (blood alcohol content) than the lighter.  But, when they reach the same BAC, they are similarly impaired.  Unless, of course, one has become "accustomed" to alcohol consumption, and has developed tolerance to alcohol, then either one would be able to  reach the same level of inebriation with the same BAC.  However, even if one were able to show a level of sobriety, their BAC would be the same, and be subjected to the same laws as one showing more inebriation.