Alcohol abuse is a term generally taken to mean drinking so much that it interferes with your ability to have a normal, productive life.

The short-term effects of excessive drinking are well-known to one and all, especially to men who may find that drinking too much decreases sexual desire and makes it impossible to . . . well . . . perform. (No evidence suggests that excessive drinking interferes with female orgasm.)

Excessive drinking can also make you feel terrible the next day. The morning after is not fiction. A hangover is a miserable physical fact:

• You’re thirsty because you lost excess water through copious urination.

• Your stomach hurts and you’re queasy because even small amounts of alcohol irritate your stomach lining, causing it to secrete extra acid and lots of histamine, the same immune system chemical that makes the skin around a mosquito bite red and itchy.

• Your muscles ache and your head pounds because processing alcohol through your liver requires an enzyme — nicotinamide adenine dinucleotide (NAD) — normally used to convert lactic acid, a byproduct of muscle activity, to other chemicals that can be used for energy. The extra, unprocessed lactic acid piles up painfully in your muscles.

Alcoholics are people who can’t control their drinking. Untreated alcoholism is a life-threatening disease that can lead to death either from an accident or suicide (both are more common among heavy drinkers) or from a toxic reaction (acute alcohol poisoning that paralyzes body organs, including the heart and lungs) or malnutrition or liver damage (cirrhosis).

Alcoholism makes it extremely difficult for the body to get essential nutrients. Here’s why:

• Alcohol depresses appetite.

• An alcoholic may substitute alcohol for food, getting calories but no nutrients.

• Even when the alcoholic eats, the alcohol in his or her tissues can prevent the proper absorption of vitamins (notably the B vitamins), minerals, and other nutrients. Alcohol may also reduce the alcoholic’s ability to synthesize proteins.

No one knows exactly why some people are able to have a drink once a day or once a month or once a year, enjoy it, and move on, while others become addicted to alcohol. In the past, alcoholism has been blamed on heredity (bad genes), lack of willpower, or even a bad upbringing.

But as science continues to unravel the mysteries of body chemistry, it’s reasonable to expect that researchers will eventually come up with a rational scientific explanation for the differences between social drinkers and people who can’t safely use alcohol. It just hasn’t happened yet.