When menstrual periods stop (amenorrhea) or become infrequent without an obvious cause, checking prolactin levels can be an important part of finding answers.

What is prolactin?

Prolactin is a hormone made by the pituitary gland, a small but important endocrine gland at the base of the brain. The role of prolactin is normally to support breast milk production after childbirth. However, outside of pregnancy and breastfeeding, high prolactin levels can disrupt normal hormonal balance.

How does prolactin affect menstrual cycles?

When prolactin levels are too high, it can block ovulation, lower estrogen levels, and interfere with the menstrual cycle—causing periods to become irregular or stop altogether. Because ovulation is essential for fertility, high prolactin can also lead to difficulty conceiving.

Common symptoms associated with high prolactin (prolactinoma):

• Infrequent or absent menstrual periods
• Fertility problems (due to ovulation suppression)
• Galactorrhea (unexpected breast milk production)
• In rare cases, if a large pituitary tumor is present, symptoms may also include:
  • Headaches
  • Loss of peripheral vision (due to pressure on the optic chiasm)
    

What causes prolactin to rise?

There are several possible causes of elevated prolactin, including:

• Stress (even the stress of a blood test!)
• Certain medications (especially antipsychotics and anti-nausea drugs)
• Small, usually benign pituitary tumors called prolactinomas that secrete prolactin 
• Other pituitary lesions that press on the pituitary stalk causing prolactin to leak out 

Why do we need to be careful about when we test prolactin?

Mild elevations in prolactin can occur naturally in response to stress, exercise, or even minor illnesses. These mild rises usually don’t cause any symptoms like missed periods or galactorrhea and , if prolactin is tested without a clear reason, it can lead to unnecessary worry and unnecessary follow-up testing.

For this reason, prolactin testing is often limited to specialists and is usually only ordered when there’s a good clinical reason—such as menstrual periods stopping or becoming infrequent without clear explanation.

What happens if prolactin is elevated?

If prolactin is found to be elevated on a properly timed blood test, your doctor will assess:

• Whether any medications could be causing the rise
• Whether imaging (such as a pituitary MRI) is needed to rule out a tumor
• Your vision (especially peripheral vision) if a large tumor is suspected
• Repeat blood tests

Treatment will depend on the cause and might include adjusting medications, starting specific treatments like dopamine agonists, or monitoring with follow-up blood tests and imaging.

The bottom line:

Prolactin testing is a simple blood test, but using it wisely—only when indicated—makes it much more powerful in helping to find the real cause and guiding the right next steps.