The most notable behavioral effects of caffeine occur after consumption of low to moderate doses (50-300 mg) and include increased alertness, energy, and ability to concentrate. Five ounces of coffee may contain 71-220 mg of caffeine. Whereas moderate consumption rarely leads to health risks, higher doses induce negative effects such as anxiety, restlessness, insomnia, and tachycardia. After sudden caffeine cessation, withdrawal symptoms develop in a modest number of cases but are typically moderate and transient. The negative effects of high-dose caffeine consumption are seen primarily in a small group of individuals who are caffeine sensitive.

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Caffeine has a half-life in plasma of 3-7 hours; this increases approximately twofold in women who are in the later stages of pregnancy or are long-term users of oral contraceptive steroids.

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The most commonly reported symptoms of caffeine withdrawal are:

• Headaches

• Fatigue

• Weakness

• Drowsiness

• Impaired concentration

• Work difficulty

• Depression

• Anxiety

• Irritability

• Increased muscle tension

• Tremor, nausea, and vomiting (occasionally)

Withdrawal symptoms generally begin 12-24 hours after sudden cessation of caffeine consumption and reach a peak after 20-48 hours. In some individuals, however, these symptoms can appear within only 3-6 hours and can last for approximately 1 week.

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Withdrawal symptoms generally begin 12-24 hours after sudden cessation of caffeine consumption and reach a peak after 20-48 hours. In some individuals, however, these symptoms can appear within only 3-6 hours and can last for about 1 week. Withdrawal symptoms do not relate to the quantity of caffeine ingested daily. For example, Strain and colleagues showed that withdrawal symptoms occur in individuals who consume 129-2548 mg of caffeine per day. Some investigators have suggested that caffeine withdrawal symptoms (but not caffeine abuse or dependence) should be recognized as a diagnosis in the American health system. The DSM-5 does include caffeine-related disorders in the substance-related and addictive disorders chapter. Caffeine withdrawal symptoms disappear shortly after ingestion of caffeine.

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In humans, tolerance to some physiologic actions of caffeine can occur. This is the case for the effects of caffeine on blood pressure, heart rate, diuresis, plasma adrenaline and noradrenaline levels, and renin activity. Tolerance usually develops within a few days. Tolerance to some subjective effects of caffeine, such as tension and anxiety, jitteriness, nervousness, and the strength of drug effect, has been shown.

Conversely, although tolerance to the enhancement of arithmetic skills has been documented, evidence of tolerance to caffeine-induced alertness and wakefulness is limited. Cerebral energy metabolism has not been found to develop a tolerance to caffeine.

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Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.

Cite this article: Amy Kao. Quiz: Are You Aware of the Neurologic Effects of Caffeine? Medscape. Mar 03, 2016.