What is the exact mechanism of the antiandrogenic effect of cimetidine?

The antiandrogenic effect of cimetidine, a first-generation H2-receptor blocker, is accompanied by hyperprolactinemia. In women, this may manifest as galactorrhea; in men, as gynecomastia and impotence. The precise molecular mechanism of cimetidine's antiandrogenic action is not specified in the provided sources.

What is the difference between cimetidine and ranitidine regarding drug interactions?

Cimetidine inhibits cytochrome P450 and microsomal oxidation, slowing down the metabolism of other drugs, whereas ranitidine does not affect the metabolism of concomitant medications.

What happens upon abrupt discontinuation of cimetidine?

A withdrawal or rebound syndrome occurs, manifested by a relapse of peptic ulcer disease.

What additional mechanism do nizatidine and roxatidine possess?

In addition to H2-receptor blockade, they stimulate protective mucus production and normalize gastrointestinal motility.

What are the specific contraindications for famotidine?

Famotidine is contraindicated in hypersensitivity, acute porphyria, as well as in children, pregnancy, and lactation.

Home › Pharmacology › H2-Receptor Blockers: Pharmacology and Clinical Use

H2-Receptor Blockers

H2-receptor blockers

For medical students2 min readUpdated 2026-10-10

H2-receptor blockers belong to the class of antisecretory drugs that inhibit hydrochloric acid production by gastric parietal cells. They decrease basal and nocturnal acid secretion and suppress pepsin output.

GenerationsFrom cimetidine (1st) to nizatidine and roxatidine (4th–5th)

MechanismHistamine blockade, reduction of hydrochloric acid and pepsin

IndicationsPeptic ulcer disease, Zollinger-Ellison syndrome

Key featuresCimetidine inhibits cytochrome P450 and causes withdrawal syndrome

Classification and Generations of Drugs

This pharmacological group is part of the antisecretory drugs, alongside proton pump inhibitors and muscarinic receptor antagonists (M-anticholinergics). H2-receptor blockers are categorized into several generations:

Cimetidine — first-generation representative.
Ranitidine — second-generation, active for up to 10–12 hours and more potent than its predecessor.
Famotidine — third-generation with a favorable tolerability profile.
Nizatidine and Roxatidine — fourth and fifth generations possessing a dual mechanism of action.

Pharmacodynamics and Mechanism of Action

These drugs block the effects of histamine released by enterochromaffin-like cells. This produces the following effects:

Inhibition of hydrochloric acid secretion by parietal cells.
Reduction of basal acid secretion at rest and during the day.
Decrease in nocturnal acid output.
Suppression of pepsin synthesis.

Later generations (nizatidine and roxatidine) additionally stimulate protective mucus production and normalize gastrointestinal motility.

Clinical Application and Dosing

These agents are used for gastric and duodenal peptic ulcer disease, hyperacid states, as well as Zollinger-Ellison syndrome and NSAID-induced ulcers.

Cimetidine: prescribed 3 times a day plus at bedtime for a course of 4–8 weeks. Abrupt discontinuation causes rebound syndrome with ulcer recurrence.
Ranitidine: taken twice daily.
Famotidine: used for acute ulcer exacerbation at a dose of 40 mg once daily at bedtime.

Side Effects and Interactions

The safety profile varies depending on the generation and specific active substance:

Cimetidine: causes antiandrogenic effects (hyperprolactinemia, galactorrhea, gynecomastia, impotence), diarrhea, and renal and hepatic impairment. It acts as a microsomal oxidation inhibitor, suppressing cytochrome P450 and slowing the metabolism of tricyclic antidepressants and anticoagulants.
Ranitidine: rarely produces adverse reactions (occasional constipation or headaches) and does not affect the metabolism of other medications.
Famotidine: is generally well tolerated, but has limitations: contraindicated during pregnancy, lactation, and in pediatric patients.

Mnemonic

Cimetidine "cramps" the endocrine system (causes antiandrogenic effects and inhibits cytochrome P450), while ranitidine and famotidine behave more calmly.

Frequently asked questions

What is the exact mechanism of the antiandrogenic effect of cimetidine?: The antiandrogenic effect of cimetidine, a first-generation H2-receptor blocker, is accompanied by hyperprolactinemia. In women, this may manifest as galactorrhea; in men, as gynecomastia and impotence. The precise molecular mechanism of cimetidine's antiandrogenic action is not specified in the provided sources.
What is the difference between cimetidine and ranitidine regarding drug interactions?: Cimetidine inhibits cytochrome P450 and microsomal oxidation, slowing down the metabolism of other drugs, whereas ranitidine does not affect the metabolism of concomitant medications.
What happens upon abrupt discontinuation of cimetidine?: A withdrawal or rebound syndrome occurs, manifested by a relapse of peptic ulcer disease.
What additional mechanism do nizatidine and roxatidine possess?: In addition to H2-receptor blockade, they stimulate protective mucus production and normalize gastrointestinal motility.
What are the specific contraindications for famotidine?: Famotidine is contraindicated in hypersensitivity, acute porphyria, as well as in children, pregnancy, and lactation.

Go deeper

Complete classification of antisecretory drugs and the role of M-anticholinergics
Comparison of proton pump inhibitors and H2-receptor blockers
Detailed analysis of Zollinger-Ellison syndrome
Impact of cytochrome P450 on the pharmacokinetics of other drug classes
Specifics of managing NSAID-associated ulcers