OBJECTIVE: To evaluate the transfer of delta-9-tetrahydrocannabinol and its metabolites into human breast milk after maternal inhalation of 0.1 g cannabis containing 23.18% delta-9-tetrahydrocannabinol. METHODS: In this pilot pharmacokinetic study, breast milk samples were collected from mothers who regularly consumed cannabis, were 2–5 months postpartum, and exclusively breastfeeding their infants. Women were anonymously recruited for the study. After discontinuing cannabis for at least 24 hours, they were directed to obtain a baseline breast milk sample, then smoke a preweighed, analyzed, standardized strain of cannabis from one preselected dispensary, and collect breast milk samples at specific time points: 20 minutes and 1, 2, and 4 hours. Quantification of delta-9-tetrahydrocannabinol and its metabolites in these collected breast milk samples was performed by high-performance liquid chromatography tandem mass spectrometry. RESULTS: A total of eight women were enrolled. Most were occasional cannabis smokers and one a chronic user. Delta-9-tetrahydrocannabinol was detected at low concentrations at all the time points beyond time zero. No metabolites were detected at any time point. Delta-9-tetrahydrocannabinol was transferred into mother's milk such that exclusively breastfeeding infants ingested an estimated mean of 2.5% of the maternal dose (the calculated relative infant dose=2.5%, range 0.4–8.7%). The estimated daily infant dose was 8 micrograms per kilogram per day. CONCLUSION: This study documents inhaled delta-9-tetrahydrocannabinol transfer into the mother's breast milk. Low concentrations of delta-9-tetrahydrocannabinol were detected. The long-term neurobehavioral effect of exposure to delta-9-tetrahydrocannabinol on the developing brain is unclear. Mothers should be cautious using cannabis during pregnancy and breastfeeding.

Aim: This study determined the transfer of intramuscular interferon β-1a into human milk and provides an estimate of infant exposure to this antiviral in six women chronically receiving intramuscular interferon β-1a (Avonex^®, Biogen Idec, Research Triangle Park, NC). Methods: Interferon β-1a was measured at various times at steady state in milk samples collected from women receiving interferon β-1a at 30 μg/week. Results: Average milk concentrations were 46.7, 97.4, 66.4, 77.5, 103.1, 108.3, 124, and 87.9 pg/mL at 0, 1, 4, 8, 12, 24, 48, and 72 hours, respectively, after dosing. Using the highest value measured (179 pg/mL), the estimated relative infant dose would be 0.006% of the maternal dose. Conclusions: These data clearly suggest that interferon β-1a does not penetrate the milk compartment significantly and that levels in milk are far subclinical. No side effects were noted in any of the breastfed infants.

Background: The impact of COVID-19 vaccination on breastfeeding is unknown. The primary aim of this study was to determine whether vaccine-related side effects following COVID-19 vaccination were associated with an adverse impact on breastfeeding. Secondarily, we sought to determine perceived symptoms in breastfed children and maternal opinion about COVID-19 vaccination. Materials and Methods: We conducted a cross-sectional survey of breastfeeding mothers who underwent COVID-19 vaccination >2 days before the survey. Subjects were recruited through social media and websites. Data included sociodemographic information, vaccine history, maternal and child symptoms, and impact on lactation/breastfeeding. Bivariate statistics (chi-square, Wilcoxon rank sum, and t tests) and multivariable logistic regression models examined the association of vaccine side effects with lactation, symptoms in breastfed children, and maternal opinion on vaccination. Results: Analysis included 4,455 breastfeeding mothers. Maternal postvaccination symptoms were more common after the second dose (p < 0.001). Overall, 77 (1.7%) respondents reported a negative impact on breastfeeding postvaccination, and these mothers were more likely to have experienced fatigue, headache, muscle pain, injection site pain, chills, fever, or allergic reactions. After adjusting for confounding variables, higher odds of an adverse impact on lactation were associated with lower breastfeeding intensity, dose of vaccine, and child symptoms. Even among mothers who reported an adverse impact on breastfeeding, maternal opinion about vaccination and confidence in their decision to receive the COVID-19 vaccine were high. Conclusions: COVID-19 vaccination among breastfeeding mothers resulted in minimal disruption of lactation or adverse impact on the breastfed child. These findings may be considered in vaccination decision-making.

Background: Aspirin has antipyretic and anti-inflammatory properties and is frequently used by pregnant and lactating women. However, its transfer in human milk when administered at low dose has not been reported. Research aim: This study aimed to evaluate the transfer of acetylsalicylic acid and its metabolite, salicylic acid, into human milk following the use of low dose aspirin. Methods: In this study, milk samples were collected at 0, 1, 2, 4, 8, 12, and 24 hours from seven breastfeeding women after a steady-state daily dose of 81 mg of aspirin. Milk levels of acetylsalicylic acid and salicylic acid were determined by liquid chromatography–tandem mass spectrometry. Results: Acetylsalicylic acid levels were below the limit of quantification (0.61 ng/ml) in all the milk samples, whereas salicylic acid was detected at very low concentrations. The average concentration of salicylic acid observed was 24 ng/ml and the estimated relative infant dose was 0.4%. Conclusion: Acetylsalicylic acid transfer into milk is so low that it is undetectable even by highly sophisticated methodology. Salicylic acid does appear in the human milk in comparatively low amounts, which are probably subclinical in infants. Thus, the daily use of an 81-mg dose of aspirin should be considered safe during lactation.