There have been some suggestions that caffeine use can cause increased risks of depression, insomnia and anxiety – even suicide has been linked to caffeine addiction. Caffeine withdrawal typically produces symptoms that are the opposite of the effects of intoxication. This effect can be extreme in those who are addicted to caffeine.
The symptom commonly noticed by people going through caffeine withdrawal is an intense headache. When reducing caffeine intake, people often feel very tired and even drowsy. There have been instances of difficulty concentrating, and feel depressed or irritable.
Very rarely, but often enough to note a mention, people withdrawing from caffeine also experience flu-like symptoms, such as nausea, vomiting, and muscle pain or stiffness.
This can overlap with work addiction, as some people use the stimulating effects of caffeine both to increase energy for and interest in the mental and physical activities associated with their jobs.