Withholding information for multiple therapeutic natural products used in organic production is not available. The objective was to determine whether the administration of a prophylactic intrauterine infusion of an oregano extract and oregano essential oils product (Optimum UterFlush (UF), Van Beek Natural Science, Orange City, IA), in postpartum dairy cows results in detectable levels of the active ingredient carvacrol (4-isopropyl-2-methylphenol) in milk. Five primiparous Holstein cows (DIM = 3.8 ± 0.4 d) were randomly selected from the fresh pen of an organic certified dairy farm. After a clinical inspection to ensure the enrolment of healthy individuals, a baseline composite milk sample was collected from each of the 5 cows. All the study cows were treated with an intrauterine infusion consisting in 3.75 mL of UF diluted in 117 mL of distilled water, applied every other day for 3 applications, as indicated by the manufacturer. Two sampling schemes were used: (1) composite milk samples were collected from all cows at 6, 12, 24 and 48 h after the first treatment administration; (2) composite milk samples were collected from a subgroup of 2 cows at 6, 12, 24 and 48 h after the last treatment. After collection, milk samples were frozen at −20°C and stored until lab analysis. The presence of carvacrol was analyzed using gas chromatograph mass spectrometry (ABC testing, Tustin, CA). Carvacrol was not detected in the baseline samples. In contrast, carvacrol was detected in all the samples collected after treatment application. Means and standard deviations were calculated using PROC MEANS from SAS. The average concentration of carvacrol reached its highest point at 6 h after the first UF infusion (0.217 ± 0.159 ppm) and then decreased to 0.084 ± 0.098 ppm at 12 h, to 0.005 ± 0.006 ppm at 24, and to 0.0006 ± 0.001 ppm at 48 h after the first treatment. Samples following scheme 2 resulted in average carvacrol concentrations of 0.097 ± 0.057 ppm at 6 h, 0.089 ± 0.068 at 12 h, 0.042 ± 0.038 ppm at 24 h, and 0.002 ± 0.002 ppm at 48 h after the last treatment. These results indicate that under the recommended dose of UF, carvacrol can be detected in milk after prophylactic intrauterine infusion.