Caffeine

Caffeine is a stimulant found in coffee, tea and many energy drinks. It is also sold in tablets and included in some medicines. People use it to feel more awake, study or get through work when they are tired.

Its familiar packaging makes it easy to overlook how much of your routine involves it: coffee at home, another at work, an energy drink later. You can become accustomed to regular use before considering whether it suits you.

By questionnaire

You may feel more awake or more wired. Some people notice a clear sensation; others notice little, especially with regular use. Responses vary.

Jitters, shaking or palpitations can accompany that alert feeling. Sleep can still be affected after the obvious stimulation has faded. Being able to keep going is not the same as having had enough rest.

Physical dependence can develop. Abruptly stopping regular use may bring headache, fatigue, irritability and trouble concentrating. Caffeine can worsen anxiety and sleep problems and interact with medicines; a pharmacist can check your combination.

Concentrated powders and liquids can cause severe, even fatal poisoning. Everyday availability does not make those products safe. Caffeine also does not reverse alcohol impairment, even if the combination makes you feel more awake.