The normal reference ranges for the prolactin (PRL) hormone are typically between 15 and 25 µg/L for women, and approximately 5 to 10 µg/L for men. Levels below these values are defined as hypoprolactinemia (low prolactin), while levels above are defined as hyperprolactinemia (high prolactin). Both low and high prolactin levels can lead to various health problems.