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.

Possible Effects on Lactation:

Histamine H2-receptor blockade is known to stimulate prolactin secretion. Cimetidine may also 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 and caused gynecomastia and galactorrhea in nonnursing individuals.[3][4] The prolactin level in a mother with established lactation may not affect her ability to breastfeed.

Alternate Drugs to Consider:



1. Somogyi A, Gugler R. Cimetidine excretion into breast milk. Br J Clin Pharmacol. 1979;7:627-9. Letter. PMID:465286
2. Knigge UP. Histaminergic regulation of prolactin secretion. Dan Med Bull. 1990;37:109-24. PMID:2188799
3. Delle Fave FG , Tamburrano G, De Magistris L et al. Gynaecomastia with cimetidine. Lancet. 1977;309:1319. PMID:68422
4. Bateson MC, Browning MCK, Maconnachie A. Galactorrhoea with cimetidine. Lancet. 1977;310:247-8. Letter. PMID:69853

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Anti-Ulcer Agents

  • Histamine H2 Antagonists

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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