Prolactin: The Overlooked Hormone Behind Unexplained Infertility & Low Progesterone

About this episode

Unexplained infertility, PMS, and low progesterone are often dismissed when labs fall “within range.” In this episode, Dr. Brendan McCarthy explains why prolactin may be the missing piece. Learn how mildly elevated prolactin can suppress ovulation, lower progesterone, and impact fertility—even when labs appear normal. We also discuss common causes, symptoms, the role of stress and medications, and why diet (including gluten sensitivity) may matter. This episode focuses on precision medicine, not fear—helping you understand what standard reference ranges often miss. Citations: Research — Prolactin and Breast Cancer Risk Below are key epidemiologic and review papers that inform the discussion in this episode regarding prolactin and breast biology. These studies look at associations, not simple cause-and-effect relationships, and help explain why prolactin shows up in breast health conversations. Meta-analysis: circulating prolactin and breast cancer risk Wang M, et al. (2016). Plasma prolactin and breast cancer risk: a meta-analysis. Cancer Causes & Control. This meta-analysis pooled data from multiple observational studies comparing women with higher versus lower circulating prolactin levels. Across studies, higher prolactin levels were associated with a modest but statistically significant increase in breast cancer risk. The association was most evident in postmenopausal women and in hormone-receptor–positive tumors. This helps explain why prolactin is considered a relevant growth signal in breast tissue rather than just a “lactation hormone.” Systematic review and meta-analysis: prolactin levels across breast cancer cohorts Aranha AF, et al. (2022). Impact of prolactin levels in breast cancer: a systematic review and meta-analysis. Endocrine-Related Cancer. This more recent systematic review and meta-analysis evaluated circulating prolactin levels across breast cancer populations and control groups. Elevated prolactin levels were associated with higher breast cance