Because of physiological differences, women become more easily intoxicated than men do. Women are more vulnerable to alcoholism. Physical changes associated with ageing can make older people easily intoxicated and more vulnerable to the effects alcohol. Some individuals report that they become more easily intoxicated on drinking alcohol when taking an SSRI. Since alcohol is a depressant, it is best to avoid it when being treated for depression.
Habitual drinkers acquire a tolerance to alcohol. This means that, to obtain the same, initial intoxicating effects, they gradually must increase the amount of alcoholic beverage that they drink. Their liver breaks down alcohol at a faster rate, necessitating a greater alcoholic intake to achieve the same level in the blood. At the same time, nerve cells in the brain become less and less responsive to a given amount of alcohol. If your ancestors drank heavily, it would take very little initial drinking on your part, to become tolerant to alcohol [or drugs].
About 25 years ago, Dr. Marc Schuckit measured responses to alcohol in young college students. None of the young men were alcoholics when they were tested. Many years later, however, he discovered that the young men who exhibited a low response to a drink of alcohol were more likely to become alcoholics in the future.
Therefore, it seems that a diminished response to alcohol appears to predict the development of alcoholism in some people. If you are easily intoxicated by small amounts of alcohol, it is unlikely that you will ever become an alcoholic. On the other hand, if you can 'hold your liquor' at an early age, you have a greater risk of becoming an alcoholic years later."