Why does coffee affects peoples mood?

Coffee usually contains a chemical called caffeine, which is a stimulant and mildly addictive. People who are used to drinking coffee may suffer withdrawal symptoms (headaches, jitters) if they don't get their regular fix.

For those who take sugar in their coffee, sugar is also an energy boost which can help people to get on with what they need to be doing.

Apart from the medical side, many people see coffee as an important part of their daily ritual, and may get irritated if they can't have it because of that