not applicable (purified compound) · supplement
Evidence tier: moderate
Caffeine is a natural stimulant found in coffee, tea, cola and chocolate. Taken late in the day, it can shorten that night's sleep.
Caffeine is a central nervous system stimulant; its receptor level mechanism (adenosine blocking is the usual textbook account) was not re verified against a named authority in this pass. It is absorbed rapidly and completely, effects begin about 15 to 30 minutes after intake and the average half life is about 4 hours, ranging from 2 to 8 hours (EFSA explainer). Its clearance depends on the liver enzyme CYP1A2: fluvoxamine prolongs caffeine's half life by inhibiting CYP1A2 (PMID 16236038), and ciprofloxacin also slows its clearance (PMID 2729942).
Caffeine is one of the most studied compounds people take. A review of 45 publications found it an effective countermeasure to the drop in thinking performance after sleep loss (PMID 31837359). A Cochrane review of shift workers found it may improve performance, but the 13 trials carried a high risk of bias and none measured injuries (PMID 20464765). Graded moderate rather than strong because most trials are short and lab based. At the 50 mg in one PlantRx strip, no benefit claim is supported: the PlantRx claims register allows only a quantity statement. The safety picture is well defined by EFSA: up to 400 mg a day and single doses up to 200 mg raise no concern for healthy adults, 200 mg a day in pregnancy and while breastfeeding, and 3 mg per kg a day for children and teenagers. Sleep is the commonest cost: a meta analysis of 24 studies found total sleep about 45 minutes shorter (PMID 36870101).
Healthy adults: single doses up to 200 mg and up to 400 mg across the day (EFSA). Pregnancy and breastfeeding: no more than 200 mg a day (NHS, EFSA). Children and teenagers: up to 3 mg per kg body weight a day (EFSA). One PlantRx Energy and Alertness strip contains 50 mg.
Effects start in about 15 to 30 minutes and the half life averages about 4 hours (2 to 8) [EFSA]. 100 mg close to bedtime can disturb sleep in some adults [EFSA]. A meta analysis suggests a cup of coffee (about 107 mg) at least 8.8 hours before bed, and a large pre workout dose (about 217 mg) at least 13.2 hours before [PMID 36870101]. Fluvoxamine and ciprofloxacin make caffeine last much longer [PMIDs 16236038, 2729942]. Keep intake steady if you take lithium [PMID 38621222].
Pregnancy: caution
Breastfeeding: caution
Active compounds: caffeine
Remedies using Caffeine · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.