Normal Prolactin Levels and Why They Can Change

Prolactin is a very important hormone for pregnancy and lactation. Here, we'll explain what normal prolactin levels are and why they might change.
Normal Prolactin Levels and Why They Can Change
Leonardo Biolatto

Written and verified by the doctor Leonardo Biolatto.

Last update: 15 December, 2022

Prolactin is a peptide hormone, which means it has the structure of a protein. Through the union of various amino acids, it forms a more complex hormone. In fact, it has the power to cause changes in the body. Here, we’ll explore what normal prolactin levels are.

Prolactin is manufactured in the pituitary gland in humans. In the pituitary gland, there are two different parts: the anterior pituitary gland in the front and the posterior pituitary gland at the back. Prolactin forms in the anterior pituitary gland, as well as other hormones like thyrotropin or luteinizing.

The cells that make it are called lactotrophs, because prolactin mainly stimulates milk production in the mammary glands. Additionally, it plays a role in the monthly menstrual cycle.

In fact, this hormone wasn’t known in the medical world before 1928. However, it’s considered to be the oldest hormonal substance in the animal kingdom. This is because it’s in several species like insects and fish.

The amount of this hormone regulates with a positive feedback mechanism. In other words, the more stimulus there is, the more the cells create it. For example, when a mother is breastfeeding, nerves send signals to the pituitary gland to make more prolactin.

What is prolactin for?

In women, prolactin is linked to the production of milk in the mammary glands. Then, the hormone instructs the breasts to make lactose, casein, and lactalbumin; proteins that make up breast milk.

Prolactin starts to increase in quantity in the pregnant woman’s body before delivery. However, other hormones, like progesterone, prevent the milk from coming out. Then, after delivery, progesterone levels drop, and prolactin can act freely for lactation.

On the other hand, in men, prolactin works on the adrenal gland. It’s not a very noticeable effect from what we know now in science. However, it could be involved in the refractory period in men after having sex.

A baby breastfeeding.

Normal prolactin levels

Like all substances that circulate in the human body, we know that prolactin has optimal functioning values to do what it has to do. These values vary:

  • Men: The normal value is to have less than 20 ng/mL in the blood.
  • Non-pregnant women: Prolactin levels should be between 2 and 29 ng/mL.
  • Pregnant women: The expected value is higher, up to 209 ng/mL.
  • Women after menopause: In these women, the margin is smaller, between 2 and 20 ng/mL.

In non-pregnant women, prolactin greater than 100 ng/mL requires intensive testing to find out the reason for the exaggerated size increase. In general, the most frequent causes are using certain medications and having small benign tumors in the pituitary gland.

The biochemical test to know the prolactin levels is through a blood draw, so it’s not very complicated. However, not everyone needs to check for this hormone. On the other hand, we do know that these people should:

  • People with infertility problems
  • Women with irregular menstrual cycles
  • Mothers who see a change in their production of breast milk
A woman experiencing cramps.

Keep reading: Menstrual Periods: Causes of Irregularity and Natural Treatments

Disease and illness from increased prolactin levels

The most common change in prolactin levels is increased prolactin in the blood. This is called hyperprolactinemia. If it happens in a non-pregnant person, it almost certainly comes from a small tumor in the pituitary gland.

These tumors are known as prolactinomas. The vast majority are benign and don’t change in size over time. A small proportion are large or tend to grow and require surgical intervention.

Also, there’s hyperprolactinemia when women do very strenuous physical activities or when they go through stages of stress. Some medications also have the adverse effect of increasing the hormone, including antidepressants. Additionally, hypothyroidism can cause increases in prolactin that don’t have any other cause.

Recent studies link obesity with high prolactin levels. It could turn out that, in some people, high prolactin levels lead to increased appetite.

Doctors caring for women with hyperprolactinemia also can’t rule out polycystic ovarian syndromeThey’ll ask for gynecological and other laboratory tests to confirm it.

In conclusion, prolactin is a fundamental hormone, especially for women, which can change. It’s important to talk to your doctor if you have gynecological or breastfeeding symptoms. Then, they can rule out hyperprolactinemia and treat it if necessary.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Pérez, J. “Fisiología de la prolactina.” Fisiología Humana. 3ª ed. Madrid: McGraw-Hill (2005): 871-9.
  • Cariño, Cecilia, et al. “Conceptos actuales sobre fisiología de la prolactina: variantes moleculares y mecanismos de acción.” Revista Investigación Clínica 45.4 (1993): 375-86.
  • Guber, Rosa Silvina, et al. “Niveles de Prolactina circulante en patologías mamarias.” Acta bioquím. clín. latinoam 37.2 (2003): 137-143.
  • Gill-Sharma MK. Prolactin and male fertility: the long and short feedback regulation. Int J Endocrinol. 2009;2009:687259. doi:10.1155/2009/687259
  • Majumdar A, Mangal NS. Hyperprolactinemia. J Hum Reprod Sci. 2013;6(3):168–175. doi:10.4103/0974-1208.121400

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.