Prolactin and Endometriosis: Is There a Link?

Quick Facts

• Prolactin is produced primarily by the pituitary gland.
• It is involved in lactation but also influences reproductive and hormonal function.
• Some research has found higher prolactin concentrations in women with endometriosis compared with control groups.
• Higher concentrations have also been reported in some women with more advanced stages of endometriosis.
• This does not mean that raised prolactin causes endometriosis.
• Prolactin is not currently a diagnostic test for endometriosis.
• Raised prolactin can occur for many other reasons including stress, medication, pregnancy and pituitary conditions.
• An abnormal prolactin result should therefore be interpreted within the wider clinical picture

What Is Prolactin?

Prolactin is a peptide hormone produced predominantly by the anterior pituitary gland, a small gland located at the base of the brain.

Its most recognised function is stimulating breast milk production following childbirth.

However, prolactin also interacts with reproductive hormones.

When prolactin becomes significantly elevated, it can interfere with the release of gonadotropin-releasing hormone and subsequently affect LH and FSH signalling.

This may influence:

• Ovulation
• Menstrual regularity
• Oestrogen production
• Testosterone production
• Libido
• Fertility

Persistently raised prolactin is known as hyperprolactinaemia.

What Has Prolactin Got to Do With Endometriosis?

Researchers have investigated whether prolactin concentrations differ between women with and without endometriosis.

One study published in 2019 looked at 215 women experiencing infertility, including women diagnosed with different stages of endometriosis and a control group without the condition.

The researchers found that prolactin concentrations tended to be higher among women with endometriosis.

There also appeared to be a relationship between prolactin concentration and disease severity.

Mean prolactin concentrations reported within the study were approximately:

• 17.88 ng/mL in the control group
• 23.42 ng/mL in women with stage I–II endometriosis
• 31.62 ng/mL in women with stage III–IV endometriosis

The researchers also reported a greater prevalence of hyperprolactinaemia among the women with endometriosis.

That makes prolactin an interesting area of research.

But it does not make prolactin an endometriosis test.

Does Endometriosis Cause High Prolactin?

We cannot currently say that.

Finding an association between two things does not establish that one causes the other.

There are several possible explanations for why prolactin might differ between groups.

Endometriosis is a complex condition involving inflammatory, hormonal, immune and neurological pathways. Chronic pain and physiological or psychological stress may also influence prolactin secretion.

Alternatively, altered prolactin signalling could potentially interact with reproductive physiology in ways that researchers do not yet fully understand.

More research is needed to determine whether prolactin has a direct role in the condition or whether the observed relationship is secondary to other processes.

Association is not causation.

Could Prolactin Be Used to Diagnose Endometriosis?

At present, no.

Although individual studies have identified differences in prolactin concentrations, there is not enough evidence to use a prolactin blood test to diagnose or rule out endometriosis.

A normal prolactin result does not exclude endometriosis.

Likewise, a raised prolactin result does not mean that someone has endometriosis.

This distinction is particularly important because prolactin is a hormone that can fluctuate for numerous reasons.

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What Else Can Cause Raised Prolactin?

An elevated prolactin result can occur for many reasons, including:

• Pregnancy and breastfeeding
• Stress
• Sleep
• Recent exercise
• Sexual activity
• Nipple or breast stimulation
• Certain medications
• Hypothyroidism
• Polycystic ovary syndrome in some individuals
• Kidney or liver dysfunction
• Pituitary conditions such as a prolactinoma

Even the stress associated with having blood taken can cause a temporary increase in prolactin in some people.

This is why mildly elevated results are sometimes repeated under controlled conditions before further investigation is considered.

What Symptoms Can High Prolactin Cause?

The symptoms of hyperprolactinaemia depend partly on the degree of elevation and the individual.

Possible symptoms can include:

In women:

• Irregular periods
• Absent periods
• Reduced fertility
• Reduced libido
• Vaginal dryness
• Unexpected milk production

In men:

• Reduced libido
• Erectile dysfunction
• Reduced testosterone
• Fertility difficulties
• Occasionally breast tissue enlargement or nipple discharge

This is important because prolactin is not exclusively a women’s hormone.

It has clinically relevant effects in both sexes.

Endometriosis Is More Than an Oestrogen Story

Endometriosis is often described primarily as an oestrogen-dependent condition.

Oestrogen is undoubtedly important, but reducing endometriosis to one hormone oversimplifies what is a complex disease.

Research continues to investigate interactions involving:

• Oestrogen
• Progesterone
• Inflammatory signalling
• Immune function
• Angiogenesis (blood vessel creation)
• Neuroendocrine pathways
• Prolactin and other signalling molecules

Understanding these relationships may eventually help researchers better characterise different biological patterns of endometriosis.

But many of these areas remain under investigation.

Should Prolactin Be Tested If You Have Endometriosis?

Not everyone with endometriosis automatically requires prolactin testing.

However, prolactin may be relevant where someone also experiences symptoms such as:

• Irregular or absent menstrual cycles
• Fertility difficulties
• Galactorrhoea
• Reduced libido
• Unexplained reproductive hormone abnormalities

Testing should be guided by someone’s symptoms, medical history and wider hormonal picture rather than performed simply because they have an endometriosis diagnosis.

The My Atlas View

The emerging research surrounding prolactin and endometriosis is interesting because it highlights how much we are still learning about the wider biology of endometriosis.

But one research association should never be turned into a diagnostic claim.

Prolactin cannot currently diagnose endometriosis, nor should a raised result automatically be attributed to the condition.

Instead, it is another example of why biomarkers are most valuable when they are interpreted together rather than in isolation.

For someone experiencing menstrual changes, fertility difficulties or symptoms suggestive of hormonal dysfunction, looking at the wider hormonal and clinical picture can help determine what should be investigated next.

Frequently Asked Questions

Can endometriosis cause high prolactin?

Some studies have found higher average prolactin concentrations among women with endometriosis, but this does not prove that endometriosis directly causes raised prolactin.

Is prolactin a marker for endometriosis?

Not currently. Prolactin is not an established diagnostic biomarker for endometriosis.

Can high prolactin affect fertility?

Yes.

Persistently elevated prolactin can interfere with reproductive hormone signalling and ovulation, which can contribute to fertility difficulties.

Can stress increase prolactin?

Yes.

Both physical and psychological stress can temporarily increase prolactin concentrations, which is one reason an unexpected mild elevation may sometimes need repeating.

Does a normal prolactin result rule out endometriosis?

No.

A normal prolactin result cannot rule out endometriosis.

What hormones should be tested for endometriosis?

There is currently no routine blood hormone panel that can diagnose endometriosis.

Hormone testing may nevertheless be useful where symptoms suggest another hormonal abnormality or when investigating menstrual irregularity or fertility.

Study Referenced
Mirabi P, et al. Prolactin concentration in various stages of endometriosis in infertile women. JBRA Assist Reprod. 2019;23(3):225–229. doi:10.5935/1518-0557.20190020.