Users often appear successful and well adjusted.
High doses of caffeine may cause nausea, diarrhea, sleeplessness, headache, heart palpitations, trembling, and nervousness. Misuse of tablets can cause convulsions, breathing failure, and death. Individuals with livers damaged by use of alcohol can accumulate un-metabolized caffeine to toxic levels. Coffee is a source of cadmium, a toxic heavy metal related to heart disease. Sugar in foods as well as added to coffee can temporarily remove fatigue, mild depression, and cravings to drink, but it aggravates blood-sugar problems, and withdrawal can cause depression, mental confusion, irritability, and strong cravings to drink or use.