Prolactin Hormone

Prolactin is a hormone produced by a small gland at the base of the brain. It has numerous functions in the body, but it’s especially important for allowing mothers to breastfeed their babies. Outside of pregnancy and breastfeeding, prolactin levels are usually relatively low in most people.

If prolactin levels are abnormally high, there are a range of possible causes. Symptoms of elevated prolactin can range from mild to moderate, while some people may not experience any symptoms at all.

Prolactin is a hormone that’s produced by the pituitary gland. The pituitary gland is a small, oval-shaped gland that sits at the base of the brain. Even though it’s connected in the brain, the pituitary is an endocrine gland. This means that it releases various hormones into the bloodstream. In addition to prolactin, some other hormones secreted by the pituitary include growth hormone, luteinizing hormone, and follicle-stimulating hormone. 1 2

There are specialized cells in the pituitary responsible for prolactin hormone production – these are called lactotrophs. In pregnancy, when more prolactin is needed, the number of lactotrophs in the pituitary increases. 3

Prolactin function is largely regulated by the hormone, dopamine. In people who are not pregnant or lactating, dopamine prevents prolactin levels from getting too high. 2

The prolactin hormone has a large number of functions in the human body but its main function is the control of lactation, or milk production. In pregnant people, it also helps prepare the breast tissue for breastfeeding. 2

People who are not pregnant or breastfeeding do not need high prolactin levels to function. However, the hormone becomes very important in late pregnancy and after birth. Towards the end of pregnancy, prolactin prepares the breast for breastfeeding.

After the baby is born, and estrogen levels drop, prolactin begins to facilitate milk production in the breast. By working in conjunction with another hormone, oxytocin, it triggers what is known as the ‘let-down reflex’. While prolactin tells the breast to produce milk, oxytocin allows for it to be released from the breast. Nipple stimulation, whether through suckling by the newborn or through breast milk pumping, is a key driver of this process. 1 3

When not pregnant or lactating, prolactin levels are low in women, and they are always low in men. They also do not fluctuate with the menstrual cycle. The following are cited as normal prolactin level ranges: 1

• Women: 2-30 ng/ml
• Men: 2-18 ng/ml
• Pregnant people (3rd trimester): 10-210 ng/ml

After birth, prolactin levels only stay high as long as breastfeeding continues. Suckling triggers the mechanism that allows for prolactin to be secreted, and consequently for milk to be produced. If breastfeeding does not take place, prolactin drops back to its baseline levels within 2 weeks. 1

High prolactin is normal in pregnancy and after giving birth. However, elevated prolactin levels in men and women who are not pregnant or lactating are suggestive of an underlying issue, as prolactin levels in these groups are usually very low and stable. Having too much prolactin circulating in the body is called hyperprolactinemia. 3 4

Hyperprolactinemia has a number of different causes. The most common cause of abnormally elevated prolactin is a pituitary adenoma, sometimes also called a prolactinoma. This is a type of benign tumor that grows on the pituitary gland. Prolactinomas can range in size, from very small, asymptomatic tumors to very large ones that can cause bothersome symptoms. The reduction in the ability to see out of the outer halves of both of your eyes is a characteristic symptom of large pituitary adenomas. 4

If a blood test shows that your prolactin levels are high and your doctor suspects that you might have a prolactinoma, they will refer you for further testing. This will most likely be a CT or MRI scan of your brain to help visualize the pituitary and determine the size of the prolactinoma. The treatment of prolactinomas can be medical or surgical. 3

Other possible causes of hyperprolactinemia include an underactive thyroid, and a group of medicines called dopamine antagonists, which include some antipsychotics. If you are found to have elevated prolactin, your doctor should discuss all of these potential causes with you. 2

Certain symptoms may point towards having high or low prolactin, although abnormally low prolactin is very rare. If you find yourself experiencing any of these symptoms, it might be worth discussing a prolactin test with your doctor.

In women, high prolactin disrupts the work of the ovaries, decreasing estradiol levels. Because of this, symptoms of hyperprolactinemia can be very similar to symptoms of low estradiol. 2 These can include: 4

• Irregular periods
• Infertility
• Decreased libido
• Hot flashes
• Vaginal dryness
• Osteoporosis

In men, high prolactin stops the testes from functioning correctly, resulting in reduced testosterone production. Therefore, hyperprolactinemia in men presents similarly to other conditions causing low testosterone. 2 Some symptoms of high prolactin in men include: 4

• Erectile dysfunction
• Reduced energy
• Muscle wasting
• Decreased libido
• Anemia
• Osteoporosis

In both men and women, hyperprolactinemia can cause galactorrhea – the leakage of milky discharge from the nipples. 1

Large prolactinomas can also cause symptoms by pressing on different structures in the head. These include the loss of vision out of the outer halves of both eyes (bitemporal hemianopia) or persistent headaches. 3

It is important to keep in mind that hyperprolactinemia can also be asymptomatic. 1

Q: What is a prolactin test?

A: This is a simple blood test to check for the amount of prolactin circulating in your blood. It is performed if low or high prolactin levels are suspected. Samples should be taken a few hours after waking up in the morning. 3

Q: When and how to lower prolactin?

A: If you are diagnosed with prolactinoma, you may be prescribed a type of medicine called a ‘dopamine agonist’ to lower your prolactin levels. If these do not work or your prolactinoma is very large, you may be referred for minimally-invasive pituitary surgery. 4

Q: How to increase prolactin?

A: Prolactin production is tied to nipple stimulation, so pumping breast milk more frequently can help lactating women increase their prolactin levels.

Q: Can I take a prolactin supplement to increase my prolactin levels?

A: Currently, there are no widely available prolactin supplements.

Q: What is the link between prolactin and seizures?

A: Research has suggested that prolactin levels measured after a seizure can help determine if the seizure was epileptic or not. However, findings in this field are not conclusive. 5

Q: Is high prolactin a sign of cancer?

A: Elevated prolactin levels in men and women who are not pregnant or breastfeeding are usually caused by a type of pituitary tumor called a prolactinoma. Prolactinomas are benign, meaning that they are not cancerous.