Caffeine is a mild stimulant that has been consumed by humans in various forms possibly as far back as 4,700 years ago. According to a 2003 study conducted by the Johns Hopkins Bayview Medical Center, caffeine is the most widely used mood-altering substance in the world. In moderation, caffeine can produce a pleasant change in mood and a heightened alertness, but it can also lead to anxiety and nervousness. In sensitive individuals, it might only take a small amount to produce a change in mood. Caffeine can be found in coffee, soft drinks, diet supplements and energy drinks. It also comes in tablet form, usually with the purpose of keeping you awake or to suppress your appetite.
Positive Effects on Mood
As anybody who consumes coffee in the morning knows, caffeine produces a feeling of alertness and alleviates fatigue. Users also report improved concentration and focus and a boost in energy. In a 2007 study conducted at the The University of Western Australia, students were divided into two groups. 60 minutes prior to a 75-minute class, one group was given a low dose of caffeine and the other group was given a placebo. The group who received the caffeine felt more awake, clear-minded, energetic and alert than the placebo group, and they also reported a greater ability to concentrate. For the majority of healthy adults, low to moderate doses of caffeine --- about 200 to 300 milligrams, or two to four cups of brewed coffee a day --- is a safe amount and should be enough to produce the positive effects of caffeine, according to the Mayo Clinic.
Negative Effects on Mood
While the 2007 Australian study did show an enhanced, positive effect on mood in students ingesting caffeine, even at the lower dose that was administered students reported increased anxiety. If taken in amounts over 500 to 600 mg a day, caffeine can cause increased nervousness, irritability, restlessness and sleeplessness. It might also cause an upset stomach, rapid heartbeat or muscle tremors. The physical effects can further add to feelings of anxiety and nervousness. If you are particularly sensitive to caffeine, you may experience the changes in mood with even lower doses.
Withdrawal and Tolerance
Caffeine affects the central nervous system and is considered a psychoactive drug. As with similar drugs, you can develop a tolerance to caffeine, meaning you will need more and more caffeine over time to achieve the same effects. Complete tolerance to the mood-changing effects of caffeine can happen in as little as 18 days when consuming amounts of 900 mg a day, according to Roland R. Griffiths and Geoffrey K. Mumford in their article "Caffeine: A Drug of Abuse?" Complete tolerance means a substance will no longer have a specific effect, no matter how much you take. Because of this effect on the body, if you are a habitual user of caffeine and you stop taking it, withdrawal symptoms can occur. Symptoms can include irritability, headache, lack of concentration, fatigue and drowsiness. Insomnia may develop and you may experience stomach pain, upper body pain and painful joints. Withdrawal symptoms typically kick in about 12 to 24 hours after you stop ingesting caffeine and may last one to five days.
Considerations
Two hundred to 300 mg of caffeine -- one to two cups of coffee -- is usually a safe amount for healthy adults. Consume any more than that, and your mood may start to be negatively affected. If you don't consume caffeine regularly or are sensitive to caffeine, you may experience changes in mood after consuming an amount below 100 mg. Caffeine can interact with certain medications and with certain medical disorders. To avoid interactions, read all labels carefully, as many products contain caffeine. Consult with your doctor before consuming caffeine if you have medical issues such as heart disease or thyroid problems.
References
- MayoClinic.com; Caffeine: How Much is Too Much?; March 2011
- American College of Neuropsychpharmacology; Caffeine : A Drug of Abuse?; Roland R. Griffiths and Geoffrey K. Mumford; 2000
- Johns Hopkins Bayview Medical Center; Use and Common Sources of Caffeine; Griffiths et al.; July 2003
- "Advances in Physiology Education"; Influence of Caffeine Ingestion on Perceived Mood States, Concentration, and Arousal Levels During a 75-min University Lecture; Peter Peeling and Brian Dawson; 2007
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