Guaifenesin

Pregnancy

MotherToBaby says guaifenesin is not expected to greatly increase birth defects, while noting a few studies with possible associations; it says miscarriage effects are unknown and studies of preterm birth, low birth weight, and later learning have not been done. A US National Birth Defects Prevention Study case-control analysis (Cao et al., 2021; deliveries October 1997 to December 2011) assessed guaifenesin without dextromethorphan. The neural tube defect exposure window was the month before pregnancy through the first pregnancy month; the non-neural tube defect window extended through the third pregnancy month. For guaifenesin alone, the adjusted odds ratio was 1.8 (95% CI 1.0 to 3.3) for all neural tube defects and 2.2 (1.1 to 4.3) for spina bifida. The study included 1,644 neural tube defect cases and 10,409 controls, plus 15,110 non-neural tube defect cases and 10,671 controls. Guaifenesin-only exposure was reported by a small share of mothers; dose was not recorded. The authors cautioned that the small exposure proportions and many comparisons mean these findings may be true signals or chance. The study reported additional guaifenesin-only signals for small intestinal atresia or stenosis and omphalocele, with imprecise estimates. A 2025 single-hospital retrospective study of 526 pregnancies reported an association between broad antitussive and phlegm-reducing medicine groups and spontaneous abortion, but it did not provide guaifenesin-specific results and cannot establish a guaifenesin-specific risk. In a rat study (Shabbir et al., 2016; 25 pregnant rats, five per group), oral doses of 250, 350, 500, or 600 mg/kg were given on gestation days 6 to 17. The authors reported maternal and fetal findings at all test doses and did not identify a no-effect level. These animal results do not establish human outcomes. A 2025 FDA label for HYCOFENIX, a hydrocodone, pseudoephedrine, and guaifenesin combination, repeats rat findings at about 2 and 3 times the maximum recommended human dose. Its pregnancy recommendation and opioid boxed warning apply to that combination, not single-ingredient Mucinex. The Mucinex Maximum Strength OTC label says to ask a health professional before use during pregnancy.

Breastfeeding

LactMed and MotherToBaby report that published studies have not examined guaifenesin levels in human milk or effects in nursing infants. LactMed states that usual maternal doses are unlikely to harm an infant, especially one over two months, but its statement is an estimate rather than a finding from direct milk or infant measurements. Janusmed advises against breastfeeding use because clinical data are missing and infant risk cannot be assessed. The UK Robitussin Chesty Cough Medicine product information states that guaifenesin is excreted in milk in small quantities; this conflicts with LactMed and MotherToBaby, and the statement was not linked to a primary milk study in the records reviewed. The Robitussin product is an ethanol-containing liquid, not Mucinex Maximum Strength extended-release tablets, so its product-specific statement should not be generalized to Mucinex. LactMed and MotherToBaby advise avoiding products with high alcohol content or choosing alcohol-free products during breastfeeding.

What was tested

The human pregnancy study was a multisite US population-based case-control analysis using National Birth Defects Prevention Study data from 1997 to 2011. It compared maternal reports of guaifenesin alone, dextromethorphan alone, and both medicines during defined early-pregnancy exposure windows. Mothers reported medication names, timing, and frequency, but not dose. The animal study used 25 pregnant rats divided among a control group and four guaifenesin dose groups; the treated groups received 250 to 600 mg/kg orally from gestation day 6 through day 17. No human study of guaifenesin transfer into milk or effects in nursing infants was located in the PubMed search reviewed for this entry.