Caffeine is a naturally occurring alkaloid and a central nervous system stimulant found in coffee, tea, cocoa, and several other plants. Chemically, it belongs to the xanthine class and acts by blocking adenosine receptors, which promotes alertness and reduces fatigue. The use of caffeine-containing beverages dates back thousands of years: tea was consumed in China around 2737 BCE, and coffee use became popular in the Arab world in the 15th century, eventually spreading to Europe by the 17th century. Isolated for the first time in 1819 by the German chemist Friedrich Ferdinand Runge, caffeine has since become one of the most widely consumed psychoactive substances in the world, used not only in beverages but also in medicines, energy drinks, and food products. Its historical and cultural significance, along with its physiological effects, has made caffeine a subject of both scientific research and daily human consumption.
BRAND NAMES
- NoDoz – over-the-counter caffeine tablets
- Vivarin – caffeine tablets for alertness
- Jet-Alert – caffeine pills and gum
- Cafcit – liquid caffeine, often used in hospitals
- Excedrin – pain reliever that contains caffeine (combined with acetaminophen and aspirin)
MECHANISM OF ACTION
Caffeine works by blocking adenosine receptors in the brain, which normally promote sleep and relaxation. This increases alertness and reduces fatigue. It also boosts the release of neurotransmitters like dopamine and norepinephrine, improving mood, focus, and physical performance.
PHARMACOKINETICS
Absorption
Caffeine is rapidly absorbed from the gastrointestinal tract, usually within 30–60 minutes after ingestion. It is highly bioavailable, meaning most of the consumed caffeine enters the bloodstream. Peak plasma levels are typically reached within 1 hour, allowing it to quickly exert its stimulating effects.
Distribution
Caffeine is widely distributed throughout body tissues, including the brain, heart, lungs, liver, and kidneys. Its volume of distribution (Vd) is approximately 0.6 L/kg in adults. Caffeine readily crosses the blood-brain barrier and the placenta, which allows it to exert central nervous system effects.
Metabolism
Caffeine is primarily metabolized in the liver by the enzyme cytochrome P450 1A2 (CYP1A2). It is broken down into three main metabolites: paraxanthine (about 84%), theobromine(about 12%), and theophylline (about 4%). These metabolites contribute to caffeine’s stimulating and physiological effects. The rate of metabolism can vary depending on genetics, age, liver function, and concurrent drug use.
Excretion
Caffeine is mainly excreted through the urine as its metabolites, including paraxanthine, theobromine, and theophylline. Only a small portion of unchanged caffeine is eliminated. The half-life of caffeine in healthy adults is typically 3–5 hours, but it can be longer in newborns, pregnant women, or individuals with liver impairment.
PHARMACODYNAMICS
Caffeine stimulates the central nervous system by blocking adenosine receptors, which reduces fatigue and increases alertness. It also boosts neurotransmitters like dopamine and norepinephrine, enhancing mood, focus, and physical performance, while mildly stimulating the heart and metabolism.
ADMINISTRATION
Caffeine is given orally, intravenously, or rectally. Adults usually take 100–200 mg orally, while neonates receive 20 mg/kg IV followed by 5–10 mg/kg/day. It’s used for alertness, headaches, or neonatal apnea, with caution in heart or anxiety disorders.
DOSAGE AND STRENGTH
Caffeine dosage varies depending on the form and purpose. For adults, oral caffeine tablets or beverages are typically 100–200 mg every 3–4 hours as needed, not exceeding 400 mg per day. In clinical settings, intravenous caffeine citrate may be used for neonatal apnea, with doses usually 5–10 mg/kg once daily. Dosage should be adjusted in children, pregnant women, and individuals with liver impairment.
DRUG INTERACTIONS
Caffeine can interact with stimulants, certain antibiotics, and oralcontraceptives, which may increase its effects. CNS depressants may be less effective, while liver enzyme inducers or inhibitors can speed up or slow down caffeine metabolism.
FOOD INTERACTIONS
Foods like grapefruit juice can slow caffeine metabolism, increasing its effects, while high-fat or sugary meals may delay absorption. Consuming multiple caffeinated products together can cause overstimulation.
CONTRAINDICATIONS
Caffeine should be avoided in people with hypersensitivity, uncontrolled heart conditions, severe anxiety, or hypertension. Caution is also needed during pregnancy, breastfeeding, hyperthyroidism, or peptic ulcers, as it may worsen these conditions
SIDE EFFECTS
OVERDOSE
Caffeine overdose can cause restlessness, rapid heartbeat, nausea, tremors, and confusion, and in severe cases, seizures or heart rhythm problems. Treatment is mainly supportive care and monitoring.
TOXICITY
Caffeine toxicity results from excessive consumption, typically over 1 gram per day in adults. It can lead to agitation, rapid heartbeat, high blood pressure, nausea, vomiting, and in severe cases, seizures or cardiac arrest. Treatment is primarily supportive care and monitoring.
