Displaying 4 results of Equilin Impurities Equilin is a naturally occurring estrogen hormone found in the urine of pregnant mares. However, the process of collecting and isolating equilin for medicinal use can lead to the presence of impurities. These impurities may include other hormones, steroids, or potentially harmful substances. Strict quality control measures are necessary to ensure the safety and efficacy of equilin-based medications.