This study was done on 62 normal adults that were recruited through newspaper advertisement and notices on boards in the community. It was done using adults who had low to moderate daily caffeine consumption, on an average of 235 milligrams a day, or the equivalent I'm about 2 cups of coffee. This is a double-blind study, which is basically that the researcher nor this subject knew who was receiving caffeine and if so in what quantities. More than 50% of the participants who did not receive caffeine experienced moderate to severe headaches, about 10% had symptoms associated with anxiety and depression, and another 10% had significantly high readings of fatigue. Nearly 15% had symptoms associated with aches and pains.

• This study was done to determine whether the abrupt cessation of daily caffeine consumption results in a withdrawal syndrome in the general population. We therefore determined the effects of abruptly ending dietary caffeine consumption in adults with a mean daily caffeine intake (235 mg per day) similar to that in the general U.S. population. Withdrawal was evaluated with tests designed to assess psychiatric and somatic symptoms and performance.

Methods

• Subjects were included in the study if they were 18 to 50 years old; had at least a high-school diploma or equivalent; had no history of psychiatric disorder; had a normal blood pressure, heart rate, and electrocardiogram; had no physical condition contraindicating the consumption of caffeine; had not used illicit drugs in the past six months; were not currently taking medication; and consumed caffeine every day, but an average of no more than 600 mg per day, based on a seven-day food diary. 
• The mean (±SD) age of the subjects was 30±8 years, their weight was 65±9 kg, and their daily intake of caffeine was 235±126 mg.

Study Design

• The subjects completed a series of tests while consuming their normal diet (base-line period) and then again at the end of each of two two-day study periods, during which they consumed a caffeine-free diet and received capsules containing in random order either caffeine in an amount equal to their individual average daily caffeine consumption or placebo. 
• Before each study period, the subjects consumed their usual diet for at least five days. Among the women, the study periods began 5 to 19 days after the last menstrual period.