Caffeine is a natural stimulant found in many plants, including coffee beans, tea leaves, cocoa pods, and kola nuts. It is the most widely consumed psychoactive substance in the world. As a methylxanthine, caffeine primarily acts on the central nervous system, affecting alertness, mood, and cognitive function. It is commonly consumed through beverages like coffee, tea, and soft drinks, as well as in chocolate and various dietary supplements. Its stimulating effects are well-documented, leading to its widespread use for improving wakefulness and combating fatigue. (MedlinePlus)
Upon ingestion, caffeine is rapidly absorbed into the bloodstream from the gastrointestinal tract, typically within 30 to 45 minutes, with peak concentrations observed around one hour after consumption. It readily crosses the blood-brain barrier. The liver metabolizes caffeine into several metabolites, mainly paraxanthine, theophylline, and theobromine, which also have psychoactive properties. The rate of caffeine metabolism can vary significantly among individuals due to genetic factors and other influences like smoking or liver disease. (NIH ODS)
Deep dive
Tap a section to expand.
Known interactions
Compound-pair rule
Synergy
L-theanine can smooth the stimulation from caffeine for calmer focus.
Commonly taken together.
Category rule: glp1 × supplement
Note
GLP-1 medications slow stomach emptying, changing how/when oral supplements absorb; rapid weight loss raises the importance of protein and micronutrients.
Time oral supplements when nausea is lowest; prioritize protein and micronutrients; discuss with your provider.
Category rule: supplement × medication
Note
Some supplements change how the body processes medications (absorption, liver enzymes, or additive effects).
Specific pairs are checked against a licensed drug database and shown with their own severity. Always confirm with your provider or pharmacist.
Compound-pair rule
Caution
Polyphenols in coffee/tea inhibit non-heme iron absorption by up to 60%.
Take iron away from coffee and tea by at least 2 hours.
Suggested separation: 2 h
Compound-pair rule
Caution
Polyphenols in coffee/tea inhibit non-heme iron absorption by up to 60%.
Take iron away from coffee and tea by at least 2 hours.
Limit caffeine when using prescription stimulants; monitor blood pressure.
Compound-pair rule
Note
High-dose caffeine may blunt some ergogenic effects of creatine in acute studies; long-term effect is minimal.
Space by 30–60 min if concerned; long-term creatine effects are unaffected.
Frequently asked
Sources referenced
["Centers for Disease Control and Prevention (CDC)", "Cochrane Library", "DrugBank", "European Medicines Agency (EMA) - Summary of Product Characteristics (SmPC) (General Reference)", "Mayo Clinic", "MedlinePlus (National Library of Medicine)", "National Institutes of Health (NIH) Office of Dietary Supplements (ODS)", "PubChem (National Library of Medicine)", "U.S. Food and Drug Administration (FDA) (General Reference for GRAS and product labels)"]
Stackwise compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician.
Related compounds
Others in the supplement category or studied for the same goals.
