NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-.

Cover of Drugs and Lactation Database (LactMed)

Drugs and Lactation Database (LactMed) [Internet].

Show details


Last Revision: October 31, 2018.

Estimated reading time: 1 minute

CASRN: 51481-61-9

Chemical structure

Drug Levels and Effects

Summary of Use during Lactation

Limited information indicates that maternal cimetidine results in infant dosages much less than those given directly to neonates. Cimetidine would not be expected to cause any adverse effects in breastfed infants, especially if the infant is older than 2 months. However, because of its potential for causing hepatic enzyme inhibition, other drugs might be preferred.

Drug Levels

Maternal Levels. After a single oral dose of 400 mg of cimetidine, the peak milk level of 5 mg/L occurred about 3 hours after the dose and was about equal to the peak serum level in a woman who had been breastfeeding for 6 months. Milk levels remained higher than serum levels for the duration of the dosing interval. With a multiple-dose regimen of 200 mg 3 times daily and 400 mg at bedtime, milk levels just prior to the doses were relatively constant between 4.9 and 6 mg/L.[1] These levels indicate that a fully breastfed infant would receive between 0.74 and 0.9 mg/kg daily which is much less than reported neonatal dosages of 5 to 10 mg/kg daily.

Infant Levels. Relevant published information was not found as of the revision date.

Effects in Breastfed Infants

Relevant published information was not found as of the revision date.

Effects on Lactation and Breastmilk

Histamine H2-receptor blockade is known to stimulate prolactin secretion. In addition, cimetidine may have additional, nonspecific actions that stimulate prolactin secretion.[2] Oral cimetidine doses of 400 mg 4 times daily increased serum prolactin by 50 to 112% in 6 patients. Cimetidine caused dose-related gynecomastia and galactorrhea in men and nonnursing women.[3][4][5] The prolactin level in a mother with established lactation may not affect her ability to breastfeed.


Somogyi A, Gugler R. Cimetidine excretion into breast milk. Br J Clin Pharmacol. 1979;7:627-9. Letter. [PMC free article: PMC1429661] [PubMed: 465286]
Knigge UP. Histaminergic regulation of prolactin secretion. Dan Med Bull. 1990;37:109-24. [PubMed: 2188799]
Delle Fave FG, Tamburrano G, De Magistris L et al. Gynaecomastia with cimetidine. Lancet. 1977;309:1319. [PubMed: 68422]
Bateson MC, Browning MCK, Maconnachie A. Galactorrhoea with cimetidine. Lancet. 1977;310:247-8. Letter. [PubMed: 69853]
Garcia Rodriguez LA, Jick H . Risk of gynaecomastia associated with cimetidine, omeprazole, and other antiulcer drugs. BMJ . 1994;308:503-6. [PMC free article: PMC2542783] [PubMed: 8136667]

Substance Identification

Substance Name


CAS Registry Number


Drug Class

  • Breast Feeding
  • Anti-Ulcer Agents
  • Histamine H2 Antagonists
  • Gastrointestinal Agents

Disclaimer: Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.


Related information

Similar articles in PubMed

  • Review Azathioprine[Drugs and Lactation Database (...]
    Review Azathioprine
    . Drugs and Lactation Database (LactMed). 2006
  • Review Ranitidine[Drugs and Lactation Database (...]
    Review Ranitidine
    . Drugs and Lactation Database (LactMed). 2006
  • Review Nizatidine[Drugs and Lactation Database (...]
    Review Nizatidine
    . Drugs and Lactation Database (LactMed). 2006
  • Review Cefazolin[Drugs and Lactation Database (...]
    Review Cefazolin
    . Drugs and Lactation Database (LactMed). 2006
  • Review Tolazamide[Drugs and Lactation Database (...]
    Review Tolazamide
    . Drugs and Lactation Database (LactMed). 2006
See reviews...See all...

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...