A man has been drinking a liter of beer every Saturday for two years now. Is he an alcoholic? Is this habit harmful to health?

In general, different countries have different criteria for what alcoholism is. In America, addiction is considered a "drink". If you drink a certain amount a month, then you are an alcoholic. Moreover, the figures are ridiculous by Russian standards.

In Russia, the criteria for alcoholism are also clearly formulated, google it. One of the symptoms is the need to drink to bring yourself back to normal.

In your case, it is too early to talk about alcoholism (once a week, one hundred grams of vodka). But it's worth checking if there is a dependency. Are you able to take a break? 5-6 weeks? From my life experience - such a test produces a revolution in the mind of a drinking person. He really begins to understand the problem. He can't explain it on the fingers. But when he tries to abstain and cannot ...

If a person drinks a liter of beer exclusively on Saturdays, and on other days, no, no, then even though I am not a doctor, I dare say that this is never alcoholism. Pathological dependence is not visible here. And a liter of beer is two cans. Also clearly not a large number. So everything is fine.

Whether a person is an alcoholic cannot be determined only by the amount of alcohol consumed.

Such diagnoses are based on a large number of factors.
For example: How much does alcohol use harm the loved ones of this person? How strongly does it affect its performance? Mood? How does he behave when drunk?