Origin and molecular targets
Caffeine is the most active CNS stimulant among the methylxanthine derivatives (which also include theophylline and theobromine). In nature, it is found in tea leaves, coffee beans, cacao, kola nuts, and certain other plants.
At the cellular level, the alkaloid acts through three main biochemical mechanisms:
- Blockade of adenosine receptors. This is the modern theory of the drug's action. Normally, endogenous adenosine performs a protective function: it accumulates during hypoxia and stimulates $\alpha$-receptors, causing hyperpolarization and cellular inhibition (protecting the brain and myocardium). Caffeine acts as a competitive antagonist—it blocks these receptors, eliminates the inhibitory effect of adenosine, and activates the cells.
- Inhibition of phosphodiesterase (PDE). The drug inhibits this enzyme, slowing down the degradation of cyclic adenosine monophosphate (cAMP). As a result, cAMP accumulates in large quantities in the tissues of the brain, heart, and other organs.
- Effect on calcium. It alters the intracellular concentration of the $Ca^{2+}$ ion.
Effects on the central nervous system and heart
The pharmacological action of caffeine often represents a balance between its central and peripheral effects.
- Central nervous system. It exerts a powerful psychostimulatory effect by stimulating the cerebral cortex. This is manifested by a reduction in the sense of fatigue, decreased need for sleep, and increased mental and physical performance. However, the outcome heavily depends on the individual type of higher nervous activity (HNA). In patients with a weak type of HNA, enhancement of inhibition and drowsiness may occur instead of excitation. In addition, caffeine possesses analeptic activity—it stimulates the vital centers of the medulla oblongata (respiratory and vasomotor centers).
- Cardiac activity. Here, two opposing influences collide. The direct (peripheral) action on the myocardium tends to cause tachycardia. The central action (stimulation of the vagus nerve centers, n. vagus) tends to cause bradycardia. The final outcome depends on which component prevails. With large doses, the peripheral effect usually dominates: tachycardia develops, myocardial oxygen demand increases, and the risk of triggering dangerous arrhythmias arises.
Effects on blood vessels, pressure, and other organs
Its effect on vascular tone is ambiguous and depends on the specific vascular bed. It results from the combination of central stimulation of the vasomotor center (constriction) and direct myotropic spasmodic/relaxant action on smooth muscle (dilation).
- Dilated: coronary arteries of the heart and renal arteries.
- Constricted: blood vessels of the abdominal cavity (except for the kidneys).
- Cerebral vessels: caffeine tonifies and constricts them, especially if they were pathologically dilated. This exact property determines the clinical efficacy of the drug in migraines—it relieves headaches of vascular origin.
- Blood pressure: in hypotension, the alkaloid increases blood pressure via direct stimulation of the vasomotor center, contributing to its normalization. In normal blood pressure, the drug practically does not change it or increases it extremely slightly.
- Other organs: it exerts a myotropic antispasmodic effect on smooth muscle (e.g., relaxes bronchi). In the kidneys, it causes a moderate increase in diuresis due to the dilation of renal vessels and the inhibition of electrolyte reabsorption in the tubules.
Clinical use and safety
In medical practice, caffeine is used as caffeine-sodium benzoate (tablets and parenteral solutions), as well as in numerous combined formulations.
Indications for use:
- As monotherapy: to increase performance, eliminate symptoms of fatigue and drowsiness, and correct hypotensive states.
- In combination therapy: for migraine, it is combined with ergot alkaloids (the drug "Cafetamine"). It also potentiates the action of non-narcotic analgesic-antipyretics and is a component of such popular drugs as "Citramon", "Sedalgin", "Coldrex", and "Pentalgin".
Safety profile:
- Side effects: insomnia, anxiety, and psychomotor agitation are possible from the CNS. Nausea and vomiting from the gastrointestinal tract. The cardiovascular system may react with tachycardia and arrhythmias. With prolonged use, tolerance and a specific drug dependence develop — caffeinism.
- Contraindications: pronounced arterial hypertension, atherosclerosis, glaucoma, and insomnia.
Briefly: answers to topical questions
How does caffeine affect the secretion of gastric glands?
Caffeine stimulates the secretion of the gastric glands. Drinking strong coffee provokes dyspepsia and enhances gastric secretion. Therefore, caffeine-containing beverages act as gastrointestinal irritants. In the treatment of peptic ulcer disease, mandatory abstinence from them is required as part of dietary therapy to reduce glandular stimulation.
What are the symptoms of acute caffeine poisoning and antidotal care measures?
Caffeine overdose leads to clonic seizures. The toxic dose of the drug is 5–10 g. Additionally, pronounced side effects from various body systems may be observed:
- Central nervous system — insomnia, anxiety, and psychomotor agitation.
- Cardiovascular system — tachycardia and arrhythmias.
- Gastrointestinal tract — nausea and vomiting.
Specific antidotal care measures for acute caffeine poisoning are not described in the sources.
How does caffeine affect carbohydrate and fat metabolism?
Caffeine activates the breakdown of carbohydrates and fats, causing hyperglycemia and energy release. The mechanism is associated with the inhibition of phosphodiesterase and the accumulation of cAMP, which activates protein kinase A. This leads to the following metabolic changes:
- Carbohydrate metabolism — glycogenolysis (the breakdown of liver glycogen into free glucose) is stimulated, and glycogen synthesis is halted due to the inactivation of glycogen synthase. Glucose enters the bloodstream, raising its blood level.
- Fat metabolism — lipolysis (fat breakdown) is activated, accompanied by energy release.
With which groups of medicinal products does caffeine enter into clinically significant interactions?
Caffeine interacts with hepatic microsomal enzyme inhibitors, analgesics, anticonvulsants, and ergot alkaloids.
- Liver enzyme inhibitors (verapamil, cimetidine, ciprofloxacin) — slow down caffeine metabolism, causing its accumulation and increasing the risk of toxic effects.
- Non-narcotic analgesics — caffeine potentiates their action (it is part of combination drugs).
- Ergot alkaloids — used together for migraine treatment.
- Anticonvulsants — the addition of caffeine reduces their sedative effect and enhances the anticonvulsant effect.
Caffeine-containing drugs also relieve headaches caused by the intake of organic nitrates.
What are the pharmacokinetic parameters of caffeine (absorption, metabolism, excretion)?
The pharmacokinetics of caffeine is partially described in the sources, covering only the metabolism and excretion stages.
- Metabolism — carried out with the participation of hepatic microsomal enzymes. The administration of inhibitor drugs (verapamil, cimetidine, ciprofloxacin) slows down the biotransformation of caffeine, leading to its accumulation in the body and a high risk of toxic effects.
- Excretion — caffeine is a weakly basic substance excreted by the kidneys. The rate of its excretion depends on urine reaction: an acidic environment (low pH) promotes ionization and accelerated elimination of the drug, which weakens and shortens its action.
Information regarding caffeine absorption parameters is absent.
To remember the vascular effects of caffeine, use the rule "Brain in tone, heart and kidneys open": the drug constricts cerebral blood vessels (which helps with migraines), but dilates coronary and renal arteries.
Class and exam questions
Why does caffeine help with migraine attacks?
It tones up and constricts pathologically dilated cerebral blood vessels, alleviating pain of vascular origin. Therefore, it is often combined with analgesics and ergot alkaloids.
Can caffeine cause drowsiness instead of alertness?
Yes, the psychostimulant effect strongly depends on the type of higher nervous activity. In individuals with a weak type of nervous system, stimulation can lead to enhanced inhibition and drowsiness.
How does the drug affect urine production?
Caffeine causes a moderate increase in diuresis. This occurs due to the dilation of renal blood vessels and the inhibition of electrolyte reabsorption in the renal tubules.
What else to study on this topic
- Comparative pharmacological activity of methylxanthines (caffeine, theobromine, theophylline)
- The role of endogenous adenosine in myocardial and CNS protection during hypoxia
- Mechanisms of drug dependence development (theism)
- Principles of synergy between caffeine and non-narcotic analgesics
- Effect of methylxanthine derivatives on bronchial smooth muscle
Master the entire topic in the «Pharmacology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Caffeine" and another 5,304 subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 116 video lessons on the subject
Other topics in the section "Agents Used in Psychiatry and Neurology"
Free video lessons: pharmacologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.