The concentration of alcohol in blood and ther person's tolerance level determines how intoxicated the person will become. The BAL determined primarily by the number of drinks and the person's weight. However, there is no way to tell for certain how a given blood alcohol level will affect a person's behavior.
Heavy drinkers have a higher tolerance to alcohol.
This means they can experience higher blood alcohol levels before appearing intoxicated. Gilman AG, Rall TW, Nies AS, Taylor P, eds. The pharmacological basis of therapeutics, 8th ed. Pergamon Press, 1990. Ray O, Ksir C. Drugs, society and human behavior.