Which specific types of adrenoceptors does ephedrine directly stimulate?

Ephedrine is a non-selective agent that interacts with both α- and β-adrenoceptors. Its action is mixed, with a predominance of the indirect component. The secondary mechanism involves a direct stimulatory effect on adrenoceptors, although it is less pronounced. The primary effect is mediated indirectly via the release of norepinephrine from presynaptic terminals.

How does ephedrine affect bronchial smooth muscle?

Ephedrine exhibits bronchodilating activity and induces bronchial relaxation. Due to this property, the drug has been used for managing bronchial asthma. Currently, ephedrine is rarely used as a single agent and is primarily included in combination formulations due to its potential to cause drug dependence.

Why does ephedrine have a longer duration of action than adrenaline?

Unlike catecholamines, ephedrine lacks hydroxyl groups on its aromatic ring. Consequently, it is virtually unaffected by monoamine oxidase (MAO), significantly prolonging its duration of action.

What is tachyphylaxis in the context of ephedrine?

It is the rapid attenuation of the hypertensive effect upon frequent drug administration (every 10–30 minutes). This is caused by the depletion of norepinephrine stores in presynaptic terminals.

How does ephedrine help treat nocturnal enuresis?

The drug operates on two levels: it stimulates the central nervous system to decrease sleep depth while simultaneously exerting a peripheral effect by increasing urinary sphincter tone.

Why should ephedrine not be combined with MAO inhibitors?

MAO inhibitors promote the accumulation of norepinephrine in nerve endings. Ephedrine triggers a sudden release of this massive neurotransmitter pool, leading to a dangerous rise in blood pressure.

Home › Pharmacology › Ephedrine Hydrochloride

Ephedrine Hydrochloride

Ephedrini hydrochloridum

For medical students2 min readUpdated 2026-10-10

Ephedrine hydrochloride is an alkaloid derived from the plant Ephedra L. and a classic representative of sympathomimetics (indirect-acting adrenoceptor agonists). The drug stimulates the release of neurotransmitters into the synaptic cleft, exerting a powerful effect on both the peripheral nervous system and the central nervous system.

Drug ClassSympathomimetics (indirect-acting adrenoceptor agonists)

Chemical StructureSimilar to adrenaline, but lacks OH groups on the phenyl ring

PharmacokineticsHalf-life ($t_{1/2}$) is 3–6 hours; eliminated via the kidneys

Regulatory StatusClassed as a doping agent; prohibited in competitive sports

Mechanism of Action

The action of ephedrine is mixed, but the indirect component dominates, which classifies it as an indirect-acting adrenoceptor agonist (sympathomimetic).

Primary (indirect) mechanism: Ephedrine penetrates presynaptic terminals (varicosities of sympathetic nerve fibers) and promotes the massive release of the neurotransmitter norepinephrine into the synaptic cleft.
Secondary (direct) mechanism: Direct, yet weakly expressed, stimulation of adrenoceptors.

Unlike plant-derived ephedrine (the levorotatory isomer), the synthetic drug is a racemic mixture. In medicine, it is used as a salt — Ephedrini hydrochloridum.

Pharmacokinetics and Metabolism

The drug is rapidly and completely absorbed from the gastrointestinal tract when taken orally (administered before meals).

The main difference between ephedrine and catecholamines (such as adrenaline) is the absence of hydroxyl groups on the aromatic ring. Due to this, it is practically not degraded by the enzyme monoamine oxidase (MAO). It is metabolized in the liver via microsomal oxidation (deamination mediated by cytochrome P450). The half-life ($t_{1/2}$) is 3–6 hours, and elimination occurs via the kidneys.

Comparison with Adrenaline and Tachyphylaxis

In terms of its pressor effect (ability to increase blood pressure), ephedrine is significantly inferior to adrenaline—achieving a comparable effect requires a dose 50 times higher. However, the duration of ephedrine's action is significantly longer (1–1.5 hours).

A critical pharmacological feature of the drug is tachyphylaxis, which is the rapid development of tolerance upon repeated administration at short intervals (10–30 minutes). Mechanism of tachyphylaxis: Frequent administration depletes norepinephrine stores in sympathetic nerve endings. Neurotransmitter release decreases, and the hypertensive effect of the drug rapidly diminishes.

Indications for Use

The clinical use of ephedrine stems from its central nervous system stimulation and peripheral effects:

Antidote therapy: Management of poisoning with central nervous system depressants (sedatives, narcotic analgesics).
Neurology: Treatment of narcolepsy (pathological excessive sleepiness).
Urology: Nocturnal enuresis. The therapeutic effect is achieved through a dual mechanism: decreasing sleep depth (CNS effect) and increasing bladder sphincter tone (peripheral effect).

Side Effects and Contraindications

Adverse reactions are associated with excessive sympathetic stimulation:

Cardiovascular system: Tachycardia, elevated blood pressure, circulatory disturbances, risk of ventricular fibrillation.
Central nervous system: Agitation, insomnia, limb tremor.
Autonomic manifestations: Anorexia, vomiting, hyperhidrosis (sweating), urinary retention.

Contraindications: Insomnia, uncompensated hypertension, atherosclerosis, ventricular fibrillation, pheochromocytoma, and hyperthyroidism.

Drug Interactions

Ephedrine requires strict monitoring during combination therapy:

MAO inhibitors (e.g., nialamide): Enhance the pressor effect of ephedrine. When MAO is blocked in nerve terminals, norepinephrine accumulates, and ephedrine triggers its massive release, which can lead to a hypertensive crisis.
Tricyclic antidepressants: Co-administration is strictly prohibited. A washout period of 2–3 weeks is required between courses.
Functional antagonism: Drugs that prevent the release of norepinephrine attenuate the action of ephedrine.

Mnemonic

Ephedrine acts like a strict boss: it does little work itself (weak direct receptor action), but forces its subordinates (norepinephrine) to work at full capacity until they are completely exhausted (depletion of stores and tachyphylaxis).

Frequently asked questions

Which specific types of adrenoceptors does ephedrine directly stimulate?: Ephedrine is a non-selective agent that interacts with both α- and β-adrenoceptors. Its action is mixed, with a predominance of the indirect component. The secondary mechanism involves a direct stimulatory effect on adrenoceptors, although it is less pronounced. The primary effect is mediated indirectly via the release of norepinephrine from presynaptic terminals.
How does ephedrine affect bronchial smooth muscle?: Ephedrine exhibits bronchodilating activity and induces bronchial relaxation. Due to this property, the drug has been used for managing bronchial asthma. Currently, ephedrine is rarely used as a single agent and is primarily included in combination formulations due to its potential to cause drug dependence.
Why does ephedrine have a longer duration of action than adrenaline?: Unlike catecholamines, ephedrine lacks hydroxyl groups on its aromatic ring. Consequently, it is virtually unaffected by monoamine oxidase (MAO), significantly prolonging its duration of action.
What is tachyphylaxis in the context of ephedrine?: It is the rapid attenuation of the hypertensive effect upon frequent drug administration (every 10–30 minutes). This is caused by the depletion of norepinephrine stores in presynaptic terminals.
How does ephedrine help treat nocturnal enuresis?: The drug operates on two levels: it stimulates the central nervous system to decrease sleep depth while simultaneously exerting a peripheral effect by increasing urinary sphincter tone.
Why should ephedrine not be combined with MAO inhibitors?: MAO inhibitors promote the accumulation of norepinephrine in nerve endings. Ephedrine triggers a sudden release of this massive neurotransmitter pool, leading to a dangerous rise in blood pressure.

Go deeper

Differences between sympathomimetics and direct-acting adrenoceptor agonists
Mechanisms of microsomal oxidation and the role of cytochrome P450
Synaptic transmission: synthesis, storage, and release of norepinephrine
Prescription and regulatory control rules for potent controlled substances
Functional antagonism and synergism in pharmacodynamics