Caffeine

Caffeine is a naturally occurring stimulant alkaloid found in coffee, tea, and other plants. It acts primarily by blocking adenosine receptors, reducing sleepiness and increasing alertness.

Adenosine receptor antagonist: A substance that blocks receptors activated by adenosine, reducing or preventing adenosine’s effects. Caffeine’s main action is antagonizing adenosine receptors, especially A1 and A2A.
Coffee: A brewed beverage made from roasted seeds of Coffea plants. Coffee is a major dietary source of caffeine worldwide.
Alkaloid: A naturally occurring nitrogen-containing organic compound, often with pronounced effects on animals. Caffeine belongs to this broad class of nitrogen-containing plant compounds.
Theophylline: A methylxanthine drug used mainly to treat airway diseases such as asthma. Like caffeine, it blocks adenosine receptors, but its clinical use and toxicity profile differ.
Adenosine: A nucleoside involved in cellular energy transfer and signaling, including regulation of sleep pressure. Caffeine blocks receptors through which adenosine promotes sleepiness.
Tea: A beverage made by steeping processed leaves of Camellia sinensis in water. Tea supplies caffeine alongside other compounds, including L-theanine.
Purine: A nitrogen-containing heterocyclic compound whose derivatives include nucleic-acid bases and signaling molecules. Caffeine’s molecular structure is based on a purine ring system.
Nicotine: An addictive alkaloid that activates nicotinic acetylcholine receptors and occurs naturally in tobacco. It is another widely used stimulant, but works through a different receptor system.
A1 adenosine receptor: A G-protein-coupled receptor that mediates several effects of adenosine in the brain and body. Caffeine’s blockade of A1 receptors contributes to reduced neural inhibition and sleepiness.
Energy drink: A beverage marketed to increase alertness, commonly containing caffeine and other ingredients. Caffeine is the principal stimulant in many energy drinks.

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