Caffeine is perhaps the most commonly consumed, unregulated psychoactive compound in the world. Caffeine is consumed daily by an estimated 90 percent of Americans, often within coffee, tea and soda pop, but also in chocolate, dietary supplements and some prescription drugs. Caffeine can lead to physical dependence and withdrawal symptoms, the most debilitating of which are severe, migraine-like headaches.
Biochemistry of Caffeine
Caffeine enters the bloodstream quickly and passes through the blood-brain barrier to cause effects in less than 30 minutes. Once in the brain, caffeine blocks the action of adenosine, a naturally occurring neurotransmitter. The actions of adenosine include suppressing neuronal activity, dilating blood vessels and increasing blood flow throughout the body and contributing to energy production, according to "Biochemical, Physiological and Molecular Aspects of Human Nutrition." Caffeine has addictive properties that can lead to physical dependence in users. The half-life of caffeine within the body is between five and six hours, causing symptoms of withdrawal to surface within 12 to 24 hours after last intake, depending on dosages.
Main Effects of Caffeine
By being an antagonist to adenosine, caffeine increases neural activity in the brain, which leads to temporarily increased mental alertness and reduced tiredness, which are the main effects that most people desire. However, caffeine also reduces blood flow to the head, by as much as 30 percent, which can lead to dizziness, confusion, reduced fine-motor skills and dull, achy headaches, as cited in "Human Biochemistry and Disease." However, it is the vasoconstriction properties of caffeine that can alleviate some types of migraine headaches, which are caused by over-dilation of arteries and too much blood flow into the head.
Mechanisms of Headache From Withdrawal
Once a person stops ingesting caffeine, the effects start to wear off within 24 hours. Within this time frame, the arteries supplying the brain react by temporarily overcompensating for the suppression of blood flow caused by caffeine. As a result, the blood vessels over-dilate, causing too much blood to enter the skull, leading to pounding, migraine-like headaches that are often described as severe. Other mechanisms that contribute to the headache include reduced blood pressure and the breakdown of an enzyme in caffeine that acts as a pain blocker. According to "The Mechanism and Management of Headache," headaches are the most common symptom associated with caffeine withdrawal, and it is estimated that one in eight people will experience severe enough pain that it interferes with their ability to work or function for at least a few days.
Other Withdrawal Symptoms
Although caffeine withdrawal is rarely considered a medical concern, it can make a person uncomfortable for at least few days and maybe as long as a week. In addition to headaches, other symptoms of caffeine withdrawal include mild depression, fatigue, sleepiness, mood instability, reduced concentration and muscle pain or stiffness, as cited in "PDR Guide to Drug Interactions, Side Effects, and Indications."
References
- "Nutritional Sciences"; Michelle McGuire; 2007
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "The Mechanism and Management of Headache"; J.W. Lance M.D. et al.; 2000
- "PDR Guide to Drug Interactions, Side Effects, and Indications"; PDR Staff; 2009
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