This information is for educational purposes only. Off-label drug use carries risks. Always consult a qualified physician before using any drug outside its approved indication.
Cimetidine
Cimetidine
Brand names: Tagamet
ORIGINALLY APPROVED FOR
Gastric Ulcers, Acid Reflux (H2 blocker)
Cimetidine has demonstrated anti-cancer effects through a unique immune mechanism: it inhibits ICAM-1 and E-selectin expression on tumour blood vessels. These adhesion molecules are exploited by circulating tumour cells to 'grab' onto vessel walls and form metastases. By blocking this mechanism, cimetidine dramatically reduces metastatic spread in animal models and human studies. Japanese RCTs in colorectal cancer showed significantly improved 10-year survival in patients taking cimetidine perioperatively.
Molecular Pathways Targeted
Mechanism of Action in Cancer
Blocks H2 histamine receptors → reduces ICAM-1 and E-selectin on tumour vasculature → prevents circulating tumour cell adhesion → reduces metastasis. Independently reduces tumour-infiltrating regulatory T-cells (Tregs) and boosts NK cell tumouricidal activity. Also inhibits VEGF-mediated angiogenesis.
Cancers Studied
Typical Off-Label Dosing
800–1600 mg daily in divided doses (400 mg four times daily in Japanese RCTs). Often used perioperatively (around surgery). Over-the-counter in some countries at 200 mg. Take with meals.
* Dosing information from research literature only. Not a prescription. Requires physician supervision.
Cautions & Drug Interactions
- Multiple drug interactions — inhibits CYP1A2, CYP2C19, CYP2D6, CYP3A4
- Can elevate levels of warfarin, phenytoin, theophylline, many other drugs
- Gynecomastia with prolonged high-dose use (anti-androgenic effect)
- Mental status changes in elderly — use caution
- Not recommended in severe kidney/liver impairment without dose adjustment
- May mask symptoms of gastric cancer if used for acid suppression