Pregnant women should restrict DayQuil use unless absolutely necessary, according to WedMD. Risks include reduced blood flow to the uterus, resulting in a decrease in oxygen for the fetus. Prolonged use also causes fetal malformations in some pregnant patients.
Although pregnant women should avoid using DayQuil, according to WebMD, it is safe for nursing mothers to use DayQuil if needed, as low levels are excreted in milk with a low risk for infants.
According to Vicks, the manufacturer of DayQuil, it is always advisable for pregnant women to consult with their physicians before using any of the company's medical products.