Caffeine and Habituation

Is caffeine addictive?

Caffeine's mild stimulant effects on the central nervous system have been well documented, with studies clearly demonstrating that this mild stimulation can be of benefit at different times during the day and night. Many road accidents occur as a result of driver fatigue (1) and a marked time of day effect is seen in relation to such accidents, peaking at around 04.00-06.00 when the circadian rhythm of sleepiness is typically at its daily maximum. Research has evaluated the effectiveness of a range of 'in-car' countermeasures, such as opening the window or increasing the volume on the radio, and these were found to be of marginal and transient benefit. (2) A fifteen minute nap and ingestion of about 150 mg caffeine, approximately 2 cups of coffee' proved to be the most effective method of alleviating driver fatigue.(3)

Later in the day, for example after lunch, a couple of cups of caffeinated coffee have been shown to alleviate the 'post lunch dip' when levels of alertness are reduced.(4) Further research has also suggested that caffeine may remove the malaise (reduced alertness, slower psychomotor performance) associated with having a common cold(5), and that night-shift workers are more alert after drinking a couple of cups of coffee during their shift.

The pleasant taste and smell of coffee, together with the beneficial effects mentioned above contribute to the popularity of coffee as a beverage.

Although many people drink caffeine-containing coffee on a regular basis, and coffee drinking may well be a habit, this does not amount to addiction but is simply a part of everyday life. Research by reputable scientists states that caffeine (7) in moderate amounts does not act on the areas of the brain related to reward, motivation and addiction. Regular consumers do not exhibit the need for compulsive self-administration in ever-increasing amounts, nor any neglect of or decline in social behaviour observed with classical symptoms of dependence.

Unlike 'illegal' drugs such as cocaine and amphetamines, The American Psychiatric Association does not recognise caffeine dependence or abuse as diagnostic categories of Psychoactive Substance Use Disorder in its Diagnostic and Statistical Manual of Mental Disorders (8), nor does the International Classification of Diseases (ICD) include caffeine in the Drug Dependence nor Non-dependent Abuse categories (9). Of course, as with all foods and drinks, it is sensible to be moderate in one's intake. Pharmacological thresholds and metabolic clearance rates for caffeine vary considerably between individuals. People generally find a level of caffeine consumption that suits them and that has no adverse effect.

The World Health Organization has stated, 'There is no evidence whatsoever that caffeine use has even remotely comparable physical and social consequences which are associated with serious drugs of abuse.

WITHDRAWAL SYMPTOMS

Normal variations in daily caffeine consumption by regular consumers, or gradual reduction in daily intake, produce no symptoms or adverse effect. However, sudden reduction or abstention by regular consumers may, in a small percentage of individuals who are sensitive to caffeine, lead to mild symptoms of withdrawal. These are commonly experienced as headache or lethargy, which last for a few days only and disappear completely, leaving no prolonged effects. One paper (10) found that about half the number of study participants suffered withdrawal headache on sudden caffeine abstention, however, these symptoms abated after a couple of days, though six percent suffered headache during periods of caffeine intake. A study conducted in 1999 (11) collected information on the prevalence and severity of caffeine withdrawal in the general population, and to determine the incidence and type of symptoms reported on sudden, or gradual cessation of caffeine consumption. Those who reduced their intake gradually reported minimal, if any, caffeine withdrawal symptoms.

The authors of the study above (11) concluded that, 'When participants are unaware of the caffeine-withdrawal focus of the study, these results suggest that both the frequency and severity of caffeine-withdrawal symptoms are much lower than found in some previous reports and that clinically significant symptoms may be uncommon events among the general population'.

A number of studies have investigated withdrawal syndrome and many people who suddenly abstain from caffeine suffer no effects whatsoever.