Caffeine
Overview
Caffeine (1,3,7-trimethylxanthine) is the world's most widely consumed psychoactive substance. It acts primarily as an adenosine receptor antagonist, blocking fatigue signaling and increasing alertness. Multiple meta-analyses confirm significant improvements in attention, reaction time, and performance under sleep deprivation. EFSA considers 400 mg/day safe for healthy adults. Tolerance develops with regular use; abrupt cessation causes withdrawal headaches.
Dosage
100 mg · Morning · Can take on empty stomach
Key Interactions
8 verified interactions found
Caffeine and synephrine (bitter orange) are both sympathomimetics. Their combination produces additive cardiovascular effects: increased heart rate, blood pressure, and risk of arrhythmia. Multiple adverse event reports exist, including deaths in the context of high-dose weight-loss supplements.
Avoid combination, especially at high doses. Contraindicated in cardiovascular disease, hypertension, or arrhythmia.
View details →Caffeine suppresses melatonin secretion and delays circadian phase. Even moderate afternoon caffeine consumption can reduce melatonin levels by up to 50% at bedtime. Taking both simultaneously is counterproductive.
Do not combine. Take melatonin only after caffeine has cleared your system (half-life ~5 hours). Avoid caffeine after 2 pm if using melatonin for sleep.
View details →Both caffeine and modafinil promote wakefulness via different mechanisms. Their combination may produce excessive stimulation, anxiety, elevated heart rate, and severe sleep disruption. Clinical benefit of combining is not established.
Avoid or use only at low doses of each. Monitor cardiovascular symptoms. Do not use after midday.
View details →Caffeine inhibits non-heme iron absorption. Studies show a 30–80% reduction in iron absorption when consumed simultaneously. The effect is primarily due to polyphenols and tannins that co-occur with caffeine in tea and coffee, but caffeine itself also contributes.
Take iron supplements at least 1–2 hours apart from caffeine intake.
View details →Green tea extract contains significant amounts of caffeine (depending on standardization). Combining with additional caffeine supplements risks exceeding the safe daily limit of 400 mg/day and may cause jitteriness, insomnia, and elevated heart rate.
Check the caffeine content of your green tea extract product and account for it in total daily caffeine intake.
View details →Scientific Sources
Frequently Asked Questions
What is Caffeine used for?
Caffeine (1,3,7-trimethylxanthine) is the world's most widely consumed psychoactive substance.
What is the recommended dosage for Caffeine?
100 mg. Morning. Can take on empty stomach.
Does Caffeine interact with other supplements?
Caffeine has 8 verified interactions. Top: Synephrine (Bitter Orange), Melatonin.
When is the best time to take Caffeine?
Morning. Can take on empty stomach.
Is Caffeine safe to combine with other supplements?
Always check interactions before combining supplements. Use VitalStack to verify your full stack for free.
Check how Caffeine fits your full stack
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Check Your Stack →Not medical advice. VitalStack is not a medical device. For personalized health recommendations, consult a healthcare provider.