The clinical features of individuals with caffeine depend-ence were described in a series of 16 cases described by Strain and colleagues (1994). Most of these individuals reported physical or psychological problems from caffeine use which had prompted multiple unsuccessful attempts to cut down or quit caffeine use, often in response to physicians’ recommendations. Most reported tolerance to caffeine and withdrawal when attempting to abstain completely. A double-blind withdrawal trial showed functional im-pairment in most cases. For the group, median daily caffeine intake was 357 mg with a wide range of 129 to 2548 mg. The preferred ve-hicle was almost equally divided between soft drinks and coffee.
It is known that the consumption of caffeine may be influenced by several different factors, which are summarized below.
Many studies have shown that caffeine in low to moderate doses (20–200 mg) produces mild positive subjective effects of increased feelings of well-being, alertness, energy, concentra- tion, self-confidence, motivation for work and desire to talk to people. The profile of positive effects with caffeine is qualita-tively similar to that produced by d-amphetamine and cocaine, which may reflect a common dopaminergic mechanism of action. High doses of caffeine (e.g., 800 mg) produce negative subjec-tive effects such as anxiety and nervousness, especially in people who are not tolerant to caffeine.
Consistent with its ability to produce mild positive subjective ef-fects, low to moderate doses of caffeine have also been shown to function as a reinforcer in humans, that is, when given the choice under experimental conditions, some people will consistently choose to consume caffeine rather than placebo.
Survey data indicate 17% of current caffeine users reported toler-ance (Hughes et al., 1998), whereas 75% of a group of caffeine dependent individuals reported tolerance (Strain et al., 1994). Although tolerance is one of the criteria for making a diagnosis of caffeine dependence (see DSM-IV-TR criteria for substance dependence), it is not clear what role the development of toler-ance may have in the development of clinical dependence upon caffeine.
Genetic studies suggest that caffeine use problems have an un-derlying biological basis, part of which may be shared with other commonly abused substances. Twin studies comparing monozy-gotic and dizygotic twins showed heritabilities of heavy caffeine use, caffeine tolerance and caffeine withdrawal which ranged be-tween 35 and 77% (Kendler and Prescott, 1999).
The conclusion suggested by the genetic studies described above is that a common genetic factor underlies joint use of caffeine, alcohol and cigarettes. This is consistent with findings of studies on the cooccurrence of use of these three substances (Kozlowski et al., 1993). A study of individuals whose pattern of caffeine use fulfilled DSM-IV diagnostic criteria for substance dependence on caffeine found that almost 60% had a past diagnosis of alcohol abuse or dependence (Strain et al., 1994).
Epidemiological studies have shown that cigarette smokers con-sume more caffeine than nonsmokers (Swanson et al., 1994).
Surveys of psychiatric patients (typically inpatients) have found high rates of caffeine consumption, particularly among patients with schizophrenia. Other groups at risk may include substance abusers (Russ et al., 1988; Hays et al., 1998) and patients with an-orexia nervosa (Sours, 1983). While preliminary work suggests there may be some factors (such as heritability) that contribute to the predisposition to use caffeine, there are no studies that have examined the possible etiologic role of such factors in the devel-opment of caffeine dependence as a specific diagnosis. Caffeine dependence, like other drug dependence syndromes, in all likeli-hood represents the interaction of social and cultural forces, and individual histories and predispositions, operating in the context of a psychoactive substance that produces pleasant subjective ef-fects and is reinforcing.
Caffeine dependence may be an unrecognized condition with a higher prevalence than is generally appreciated (see Figure 36.2). Clinicians do not typically think to inquire about caffeine use and about problematic use consistent with a diagnosis of caf-feine dependence. However, probing for evidence of caffeine dependence may be useful, and it would be reasonable to focus upon the DSM-IV criteria for dependence that are more appro-priate for a substance that is widely available and generally cul-turally accepted. Thus, the clinician should probe for evidence of tolerance, withdrawal, continued use despite a doctor’s rec-ommendation that the person cut down or stop using caffeine, use despite other problems associated with caffeine, often using larger amounts or over a longer period than intended, or per-sistent desires and/or difficulties in decreasing or discontinuing use.
The diagnosis of caffeine dependence includes symptoms that can also contribute to a diagnosis of caffeine intoxication and caffeine withdrawal, and both of these conditions should be included in the differential diagnosis of a patient with possible caffeine dependence. Since intoxication and withdrawal symp-toms can contribute to the diagnosis of dependence, conditions that overlap with these caffeine-related disorders should also be considered. When considering a patient for a possible diagnosis of caffeine dependence, the clinician should also consider other substance dependence syndromes – especially those related to stimulants – in the differential diagnosis
Caffeine is the most widely used mood-altering drug in the world. In North America, dietary surveys indicate that weekly or more frequent consumption of caffeine-containing foods occurs in 80 to 90% of children and adults (Gilbert, 1984; Hughes and Oliveto, 1997). In the USA, average daily caffeine consumption among caffeine consumers is 280 mg (Barone and Roberts, 1996). There is only one study of the prevalence of caffeine dependence in the general population based upon standardized diagnostic criteria (Hughes et al., 1998). In this random telephone survey of residents of Vermont, 162 out of the 202 surveyed participants reported current caffeine use. Employing the generic DSM-IV criteria for dependence, 30% of the 162 current caffeine users fulfilled criteria for a diagnosis of caffeine dependence by endorsing three or more dependence criteria, with 56% endorsing the diagnostic criterion of persistent desire or unsuccessful efforts to cut down or control caffeine use, 28% endorsing using more than intended, 14% endorsing caffeine use continued despite knowledge of a physical or psychological problem likely to have been caused or exacerbated by caffeine use, 18% endorsing withdrawal and 9% endorsing tolerance. These results suggest there may be a large number of people who demonstrate symptoms consistent with a DSM-defined diagnosis of caffeine dependence.
While there are no studies that have specifically examined the course and natural history of caffeine dependence, like other drug dependence syndromes caffeine dependence appears to be a chronic relapsing disorder. In the study described above by Strain and colleagues (1994), caffeine dependence participants reportedrecurrent efforts to discontinue caffeine use, with failures to dis-continue use or frequent relapses.
In a survey of physicians’ practices, it was found that over 75% of medical specialists recommend that patients reduce or elimi-nate caffeine for certain conditions including anxiety, insomnia, arrhythmias, palpitations and tachycardia, esophagitis/hiatal hernia and fibrocystic disease (Hughes et al., 1988). However, stopping caffeine use can be difficult for some people. For exam-ple, in the diagnostic study of caffeine dependence (Strain et al., 1994), subjects reported physical conditions such as acne rosa-cea, pregnancy, palpitations and gastrointestinal problems that led physicians to recommend that they reduce or eliminate caf-feine; all reported that they were unable to follow their doctors’ recommendations