Caffeine After 4 to 5 days of daily consumption, a tolerance to the stimulating effects of caffeine may appear. addiction and withdrawal syndrome in case of abrupt cessation of consumption. Signs of withdrawal with irritability, somnolence, asthenia, headache and sometimes rhinorrhea may persist for 18 to 24 hours after the last dose. In a large number of subjects, a single dose of caffeine above 1000 mg may cause signs of acute intoxication with major insomnia, confusion, skin flushes, dyspnea, and cardiac arrhythmia. Caffeine exceeding 5000 mg can be fatal.
pharmacokinetics
Caffeine is absorbed by the digestive tract very quickly and completely and reaches the brain as early as 5 minutes after ingestion. Its half-life is 4 to 6 hours. Decreased in the smoker (3 1/2 hours), it is increased in hepatic affections and in case of use of oral contraceptives.
Effects on sleep
Ingestion of caffeine 30 to 60 minutes before bedtime prolongs sleep latency, shortens total sleep time and gives a poor impression of sleep quality. It is also responsible for an increase in the duration of stage 2 sleep and a decrease in that of stages 3 and 4. The duration of REM sleep is normal or longer. The number of spontaneous awakenings from stage 2 is increased. The intensity and the duration of these effects vary according to the subjects, according to their capacity of elimination more or less fast of the caffeine. In chronic coffee drinkers, sleep disturbances may disappear over time. However, over 500 mg / day of caffeine, subjects should be encouraged to reduce or stop their consumption.