Diphenhydramine (DPH) is a common over-the-counter medication used primarily as a first-generation antihistamine to treat allergy symptoms like runny nose and sneezing. Due to its significant sedating effect, DPH is also frequently incorporated into non-prescription sleep aids. Understanding how DPH moves into breast milk and its potential effects is important for making an informed choice during the lactation period.
Understanding Drug Transfer into Breast Milk
For any medication to affect a nursing baby, the drug must first pass from the mother’s bloodstream into her breast milk, primarily through passive diffusion. Diphenhydramine is a relatively small, fat-soluble (lipophilic) molecule, which facilitates its transfer into the milk. The concentration of the drug in breast milk generally mirrors the concentration found in the mother’s plasma.
While most antihistamines transfer in amounts that result in a low relative infant dose (RID), DPH’s long half-life means it remains in the mother’s system for an extended period, leading to sustained exposure. Although small, occasional doses of 25 milligrams or less are not generally expected to cause adverse effects, the drug remains a compound of concern. The risk of transfer is also higher in the initial postpartum days when the cellular gaps between the milk-producing cells are more open.
Direct Effects on the Nursing Infant
The primary concern regarding DPH exposure in breastfed infants stems from its potent sedative effects on the central nervous system (CNS). As a first-generation drug, it readily crosses the blood-brain barrier in both the mother and the baby. This can manifest as unusual drowsiness, deep sleep, or difficulty waking the infant for feedings, which is especially concerning for newborns who need frequent nourishment.
Monitoring for signs of sedation is important, as younger infants, especially those born prematurely, have immature livers and kidneys that struggle to metabolize and excrete the drug efficiently. In some cases, infants exposed to antihistamines have also exhibited colicky symptoms and increased irritability. This reaction is known as paradoxical excitability, which is the opposite of expected sedation, and it can present as extreme fussiness or agitation.
If the infant shows concerning symptoms, such as unusual lethargy or poor feeding, the mother should consult the pediatrician immediately. Timing the dose immediately after a feeding, or before the baby’s longest sleep period, may help minimize the peak concentration the baby receives. Prolonged or high-dose use is strongly discouraged due to the cumulative risk of CNS depression.
Diphenhydramine’s Influence on Milk Production
Beyond the direct effects on the baby, DPH carries a distinct risk of negatively impacting the mother’s milk supply. This reduction is linked to the drug’s anticholinergic properties, which block the neurotransmitter acetylcholine. This anticholinergic action can interfere with the hormones responsible for lactation by lowering maternal serum prolactin levels.
Prolactin is the hormone that signals the mammary glands to produce milk, and a decrease in its levels translates directly to reduced milk volume. This effect is dose-dependent, meaning high or frequent doses pose a greater threat to the supply. The risk of decreased milk production is highest in the early postpartum period, before lactation is fully established. Once lactation is well-established, the effect of an occasional, single dose may be less pronounced.
Safer Options for Allergy Relief and Sleep Aid
Given the potential for infant sedation and the risk of reduced milk supply, healthcare providers generally recommend alternative medications for allergy relief and insomnia during lactation. Second-generation, non-sedating antihistamines are the preferred option because they are less fat-soluble and have a reduced ability to cross into breast milk. These alternatives also do not cause the same level of central nervous system effects.
Specific alternatives widely supported for use during breastfeeding include Cetirizine and Loratadine, which transfer into milk at very low levels and are not associated with adverse effects in the nursing infant. Fexofenadine is another second-generation antihistamine considered compatible with lactation. For sleep difficulties, non-pharmacological methods, such as adjusting sleep hygiene, are the safest first-line approach. When medical intervention is necessary, mothers should discuss these safer alternative medications with a healthcare professional.