Prolactin

What is Prolactin?

Prolactin, also known as lactotropin or luteotropic hormone, is a hormone produced by the pituitary gland that’s important for milk production (lactation), hence its name, and for breast development during pregnancy. However, more recent research has shown prolactin has more than 300 roles in the body involving reproduction, metabolism, fluid regulation, immunity, and behaviour^[1].

Prolactin levels usually remain low in people assigned male at birth, but high levels in men can affect male reproduction and health and are often caused by medicines, an underactive thyroid, prolactinoma, or kidney failure. Conversely, high prolactin levels are normal during pregnancy and lactation, but they can also rise after exercise or sex^[2].

The pituitary gland is a small pea-shaped gland found at the base of your brain. It’s part of the endocrine system, the body’s hormone production team. Prolactin production occurs mainly in the pituitary gland and is controlled by dopamine and oestrogen^[3].

The Importance of Prolactin in Women

Prolactin is important for several hundred functions, but its two main responsibilities in women are:

1. Mammary gland development and breast milk production

   During pregnancy, oestrogen, progesterone and prolactin stimulate the development of breast tissue and milk production. Prolactin stimulates the growth of the alveoli in the breasts, components of the mammary glands where milk production occurs. In the alveolar cells, prolactin encourages the epithelial cells to make milk components, including lactose, casein, and lipids

2. Lactation and breastfeeding

   Once the baby is delivered, progesterone levels fall, which enables the number of prolactin receptors to grow, facilitating lactogenesis (milk secretion through the nipples). Prolactin levels only increase when nipple stimulation occurs during suckling. If breastfeeding doesn’t happen, prolactin levels will fall to pre-pregnancy levels within 2 weeks^[3].

What is the Normal Range for Prolactin?

The normal reference ranges can vary between laboratories, but generally, the normal range for prolactin is as follows:

Women	102 – 496 mU/L
Men	86 – 324 mU/L

Forth data shows prolactin levels are at their highest in women of childbearing age (18 – 49) before steadily declining. Men’s levels are highest between the ages of 18 and 29 and gradually fall with increasing age.

Why Take a Prolactin Blood Test?

A prolactin test measures the amount of prolactin in your blood and is useful if you are experiencing symptoms associated with high prolactin levels, like breast milk production when not pregnant, or to test the function of your pituitary gland.

You can test your prolactin levels with other key fertility hormones by purchasing a single at-home finger prick blood test. Your sample is then analysed at one of our accredited labs. For prolactin levels, choose:

• Female Fertility Blood Test

• Male Hormones Blood Test

What Causes High Prolactin?

It’s natural for prolactin levels to rise during pregnancy and breastfeeding, but other factors can cause them to rise, including:

• Exercise

• Physical stress

• Sexual intercourse

• Nipple stimulation

• Chest injuries

• Epileptic seizures

• Eating a meal

The increases in prolactin caused by these situations are usually temporary and they will return to normal. However, there are some conditions which can cause prolonged and abnormally high levels (hyperprolactinemia):

• Prolactinomas

• Some medicines

• Certain health conditions

• Pituitary gland tumours (other than prolactinomas)

Prolactinomas and raised prolactin levels

A prolactinoma is a non-cancerous or benign tumour that develops on the pituitary gland and causes a rise in prolactin. They are the most common type of pituitary gland tumour, making up about 40% of pituitary tumours^[4]. They are most common in women aged 25 and 34. Prolactinomas are treated with medication, surgery or radiotherapy.

Medicines that increase prolactin

Some medicines are linked to raised prolactin levels. Because dopamine regulates prolactin production, any medicines that increase dopamine levels can increase prolactin.

Other medicines that may affect prolactin levels include:

• Anti-sickness medications, like Metoclopramide and acid-reducing medicines such as omeprazole

• Some antidepressants like amitriptyline and risperidone

• Some herbal medicines raise prolactin levels, like Moringa and Ayurveda^[5]

High prolactin levels caused by medication will likely reduce after you have stopped taking them. However, you should never stop taking medication without consulting your doctor.

Health conditions that cause high prolactin levels

There are several health conditions which can increase the production of prolactin by the pituitary gland. They include:

• An underactive thyroid (hypothyroidism)

• Kidney or liver disease^[6]

• Shingles

Pituitary gland tumours and high prolactin levels

There are other types of pituitary gland tumours aside from prolactinomas, that can cause increased prolactin levels. Prolactinomas are known as secreting or functioning tumours because they make hormones. Non-secreting tumours can also affect hormone levels, including prolactin, by affecting the normal pituitary tissue^[7].

Symptoms of High Prolactin

Increased blood prolactin levels can cause:

• Infertility

• Low sex drive

• Milky discharge from the nipples when not pregnant or breastfeeding

• Vision disturbances

In women, increased prolactin levels can cause the following symptoms:

• Irregular or absent periods

• Menopause symptoms like hot flashes and vaginal dryness because of reduced oestrogen levels

• Osteoporosis

High prolactin levels in men can cause symptoms such as:

• Low testosterone levels (low energy, low libido, reduced muscle mass, anaemia)

• Erectile dysfunction

• Reduced sperm production

• Breast growth and tenderness^[8]

Does prolactin cause weight gain?

There is some evidence suggesting that hyperprolactinemia causes an increased appetite and weight gain^[9]. However, medical treatment to lower prolactin levels has been shown to have a positive effect on body weight^[10].

Does high prolactin make you tired?

If high prolactin levels are caused by a tumour pressing on the pituitary gland, it may cause tiredness^[11]. Some of the causes of high prolactin, such as an underactive thyroid, can cause symptoms such as tiredness and fatigue.

Does high prolactin cause facial hair in females?

Hyperprolactinemia is one cause of hirsutism, thick dark hair growth on a woman’s face, chest, back, or buttocks^[12]. There are several treatments available for hirsutism including cosmetic treatments, medications, and weight loss if you are overweight can help^[13].

Does prolactin make your breasts bigger?

Yes, elevated prolactin levels can cause enlarged breasts in men and women. If you experience breast growth when you are not pregnant, you may also experience some swelling and tenderness.

Does prolactin affect sleep?

Research has shown that prolactin can induce rapid eye movement (REM) sleep, the time when most dreams occur and makes up approximately a quarter of your time asleep. Elevated prolactin levels may be associated with excessive daytime sleepiness^[14].

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.