Drugs that are classified as stimulants typically increase nervous system activity, particularly activity associated with the central nervous system. The consequences of such effects include increased energy, decreased perception of fatigue and an improved sense of performance. The effects are most dramatic in individuals who are tired or bored. These changes are perceived as pleasant by most stimulant users and can lead to continual use and even dependence.
CAFFEINE
Caffeine is the only drug classified as a safe and effective stimulant by the FDA and allowed to be included in OTC stimulant products. Caffeine belongs to the group of drugs classified as xanthines. The xanthines also include the agents theophylline and theobromine; however, caffeine is the only compound of this group that is administered routinely as a therapeutic central nervous system stimulant. Caffeine is the most widely used psychoactive medication in this country. It is consumed regularly by adults and children (more than 7 million kilograms consumed yearly in the United States) and is found in many popular beverages (see Table below) and OTC drug products.
PHARMACOLOGICAL EFFECTS
Caffeine affects the functioning of systems throughout the body. The following is a summary of some of those effects.
CENTRAL NERVOUS SYSTEM (CNS)
CNS stimulation resulting from caffeine consumption is significant and results in the following:
- increased sense of well-being and elevated mood
- decreased perception of fatigue and drowsiness; increased alertness
- increased flow of thoughts (however, this does not mean one's intelligence has increased )
- reduced boredom
- increased mental endurance (able to continue with intellectual activity for longer periods of time)
- increased physical endurance
Because of these pharmacological actions on brain activity, caffeine is consumed regularly by millions in order to induce wakefulness when arising from sleep or to prevent falling asleep, relieve the boredom of daily routines, and decrease the fatigue associated with tedious, long periods of work (e.g., studying for exams or long-distance driving). It should be remembered that caffeine only masks the sense of fatigue, it does not replenish energy that has been exhausted through physical and mental work. Interestingly, the CNS stimulation from caffeine consumption is much less in the alert, highly motivated individual engaged in stimulating tasks.
CARDIOVASCULAR SYSTEM
Many studies have been conducted in order to determine the influence of caffeine on the heart and blood vessels. The following effects have been reported:
- stimulates the heart and often increases contraction rate (pulse)
- has little effect on most blood vessels; an exception are the cerebral vessels (associated with the brain and possibly responsible for some types of headaches), which are significantly constricted by caffeine
It is not entirely clear whether effects caused by intermediate doses of caffeine contribute to cardiovascular disease. While it had been thought that moderate caffeine consumption has little influence on the development of cardiovascular disorders, a recent study on patients in northern California, demonstrated persons consuming 4 or more cups of coffee a day experienced a 40 percent greater incidence of heart attacks than those drinking less amounts. Obviously additional studies need to be conducted to verify these findings, but they suggest that high caffeine consumption may lead to coronary problems.
GASTROINTESTINAL TRACT
Caffeine doses greater than 100 mg enhance the production of gastric acid secretions and cause gastric irritation. Interestingly, decaffeinated coffee also stimulates gastric acid production, suggesting that caffeine is not the only compound in coffee that influences gastric juice flow.
RENAL SYSTEM (KIDNEY)
Caffeine is classified as a mild diuretic (increases urine output). In doses commonly found in OTC products (30-100 mg) this effect is slight, but detectable.
ADVERSE EFFECTS
Although caffeine was found to be safe and effective for use in OTC products by the Food and Drug Administration, this does not mean caffeine is an innocuous compound. Some undesirable side effects of caffeine administration are:
- insomnia, restlessness, and agitation
- headaches
- tremors
In individuals who consume large amounts of caffeine daily (in excess of 1000 mg/day: 10 cups of coffee), a syndrome referred to as caffeinism may develop. The associated symptoms resemble those of extreme anxiety. Sufferers of caffeinism are highly agitated over trivial matters; nervous twitches punctuate their muscle movement; their breathing is short and rapid; in severe cases, they experience visual hallucinations. It is impossible to determine accurately the incidence of caffeinism. Some experts claim this syndrome is extremely rare, while others speculate that as many as 10% of the adults in this country consume over 1000 mg of caffeine daily and experience some form of caffeinism.
Consumption of caffeine has also been linked to an increased frequency and severity of premenstrual syndrome (PMS). This interaction is dose-dependent with the PMS incidence increasing by as much as 5-fold for those women consuming 8 to 10 cups of coffee daily. The source of the caffeine (i.e., coffee, tea or cola drinks) does not appear to make a difference.
As already mentioned, there may exist a relationship between high caffeine consumption and heart attacks. Studies in the early 1970s claimed no association between the use of caffeine and heart attacks. However, the study cited above suggests that there exists 40% greater likelihood of heart attacks in people who drink four or more cups of coffee as day. Because of such results, it is recommended that especially patients with a history of cardiovascular disease avoid high caffeine use.
There are concerns about use of caffeine during pregnancy. It is known that caffeine consumed by the mother does cross through the placenta into the fetus. Studies have found that women who consume moderate or large amounts of caffeine (2-3 cups or more of coffee daily) during pregnancy are more likely to experience spontaneous abortions of the fetus than those who consume lower amounts or none. Other studies have suggested that caffeine use can also increase the likelihood of birth defects and decrease birth weight. However, these results have been criticized and were not confirmed by subsequent research. Finally, some studies have suggested that use of caffeine by females can interfere with fertility. A 1993 Yale study concluded that the more caffeine consumed, the longer it took women to conceive. Obviously, the exact effect of caffeine use during pregnancy is not well understood. Consequently, moderate use or abstinence from caffeine consumption is recommended during pregnancy by the FDA.
As little as 200 mg of caffeine (2 cups of coffee) each day may result in significant bone loss in postmenopausal women who do not consume adequate calcium. Thus, older women prone to osteoporosis may want to reduce or eliminate coffee consumption.
ABUSE POTENTIAL
Psychological and physical dependence develop in many individuals who consume caffeine regularly, over a long period of time. There is no doubt that the stimulation associated with caffeine consumption is viewed by most persons as enjoyable and partially accounts for the immense popularity of caffeine-containing beverages. Tolerance to some of the stimulant effects often develops. This is due to a compensatory adjustment the body makes in response to the continual presence of the drug. For example, there is a decrease in the insomnia and mental alertness produced by caffeine following chronic use.
A related phenomenon is that of withdrawal which occurs when regular caffeine users abruptly discontinue their habit. The withdrawal syndrome is largely subjective and begins 12-24 hours after the last caffeine dose and can persist for up to one week. Symptoms that have been associated with caffeine withdrawal include extreme nervousness, headaches, sweating, tremors, irritability, and lethargy. Occurrence of these unpleasant symptoms can discourage quitting the caffeine habit. Usually, the withdrawal phenomena are of little long-term consequence; however, occasionally they are moderately severe and can be very disruptive to one's daily activities. Even so, compared to other stimulants that encourage abuse, caffeine is considered to have low abuse potential.
THERAPEUTIC USES
Caffeine containing products are promoted for the following purposes:
o To stay awake and prevent drowsiness. Stay-awake products contain 100-300 mg caffeine/tablet and effectively reduce perception of mild to moderate fatigue; however, because of tolerance effectiveness diminishes with continual use.
o Eliminate highway fatigue. Stay-awake products are unpredictable in their effectiveness against this type of fatigue. It should be remembered that caffeine only masks, but does not eliminate, fatigue. Because of the potentially serious consequences of fatigue while driving a motor vehicle, the use of caffeine for this purpose is discouraged.
o Reverse the effects of alcohol. The stimulant effects of caffeine do not perfectly antagonize all of the depressive effects of alcohol. Consequently, the inebriated person feels more alert after the use of caffeine, but his/her coordination, reflexes, and reaction time are still greatly impaired by the presence of alcohol in the body. This drug combination could have dangerous consequences if the affected persons perceive themselves as competent to operate motor vehicles.
o Treat headaches. Caffeine alone (100-200 mg), and in combination with OTC analgesics, such as aspirin and ibuprofen, has been found to be effective in relieving mild to moderate tension and vascular headaches.
CAFFEINE-CONTAINING PRODUCTS
Because caffeine-related effects are usually viewed as pleasant and tend to reinforce the use of products that include this stimulant, some OTC analgesics and cold medicines (see Chapter 9) include caffeine as an ingredient. Recent studies have suggested that the presence of caffeine might give some therapeutic advantage to these products because moderate doses (>100mg) also appears to have analgesic effects for some types of pain.
Caffeine (100-250 mg) is also contained in all OTC medicines promoted as stimulants or stay awake products. These products are often given ridiculous brand names that imply they have some special energy properties. A recent review of a corner gas station found caffeine-containing products called "Mega Start Energy Boosters," "Megablast: High Energy Formula" and "Rich's Super Power Pak." Some of the more popular brands of these stimulant products are listed in the following table.
PRODUCTS CAFFEINE/UNIT
Caffedrine 200 mg
No Doz Tablets 100 mg
Vivarin tablets 200 mg
High Gear Gum 25 mg
Enerjets Lozenges 75 mg
CAUTIONS
Individuals with the following disorders should probably avoid the use of products that contain caffeine:
- ulcers
- severe cardiovascular diseases
- insomnia
- nervous tension
- osteoporosis
SUMMARY
There is no current scientific evidence that demonstrates the occasional use of moderate doses of caffeine (100-200 mg) adversely affects the overall health of most individuals. This drug can be effective in reducing drowsiness and prompting mental alertness in the mild-to-moderately fatigued person. However, frequent use of caffeine should be avoided. The only way to deal effectively with fatigue is to rest. Masking the fatigue with caffeine only postpones the inevitable and should not be viewed as a solution to the problem. In addition, if used excessively, tolerance develops to the stimulant action of the caffeine causing the desired effects to be diminished. If OTC stimulant products are used, consumption of caffeine-containing beverages should be reduced to avoid ingesting toxic doses of caffeine.
The combination of caffeine with other types of OTC medicines likely reinforces their use by causing a pleasant sense of general well-being in the user. If that effect is important, for most healthy people there is probably little danger in using products that contain caffeine. As mentioned above, the presence of this mild stimulant might also contribute to the pain-relieving action of some OTC analgesics especially related to tension and vascular headaches.