# Thyroid Disorders and High Prolactin: The Blood Tests People Skip

> Two straightforward blood tests, two genuinely reversible causes of erectile dysfunction — and both are routinely left off the workup because nobody thought to ask for them.

- **Source:** ED Treatment Guides (https://www.edtreatmentguides.com/causes/thyroid-and-prolactin)
- **Last updated:** 2025-11-18
- **Type:** cause
- **Category:** Hormonal
- **Mechanism:** Thyroid hormone sets the metabolic rate of every tissue; prolactin suppresses the hormonal axis that produces testosterone.
- **See a doctor promptly if:** Headaches with visual field loss — this can indicate a pituitary tumour; Milky nipple discharge (galactorrhoea); Rapid unexplained weight change with palpitations or heat intolerance; Very low testosterone in a young man

## Key points

- Both underactive and overactive thyroid are associated with sexual dysfunction, and both are usually reversible with treatment.
- Hypothyroidism tends to associate more with erectile dysfunction and delayed ejaculation; hyperthyroidism more with premature ejaculation.
- High prolactin suppresses the signal that tells the testicles to make testosterone — producing low libido and ED with a **low or normal** LH.
- The classic trigger for checking prolactin is low testosterone that is not accompanied by a raised LH.
- Antipsychotics, metoclopramide and some other common drugs raise prolactin. So does a pituitary tumour — which needs excluding.

## Thyroid disorders

Thyroid hormone regulates the metabolic rate of essentially every tissue, so it is unsurprising that both directions of imbalance affect sexual function. What is surprising is how rarely thyroid function is checked in a man presenting with erectile dysfunction.

**How each presents**

|  | Hypothyroidism (underactive) | Hyperthyroidism (overactive) |
| --- | --- | --- |
| Sexual pattern | More often erectile dysfunction, low libido, delayed ejaculation | More often premature ejaculation; ED also reported |
| General symptoms | Fatigue, weight gain, cold intolerance, constipation, dry skin, low mood | Weight loss, heat intolerance, palpitations, anxiety, tremor, loose stools |
| Related hormones | Can raise prolactin, adding a second mechanism | Raises SHBG, which lowers free testosterone |
| Reversibility | Sexual symptoms commonly improve once treated and stable | Commonly improve once treated and stable |

> **Tip**
>
> The test is a TSH, usually with free T4. It is inexpensive, widely available, and worth requesting explicitly if your workup did not include it — particularly if you have any of the general symptoms above.

## High prolactin (hyperprolactinaemia)

Prolactin is best known for lactation, but in men its main relevance is that raised levels suppress gonadotropin-releasing hormone. Less GnRH means less LH, less LH means less testosterone — and the result is low libido and erectile dysfunction, often with fatigue and low mood.

### The diagnostic clue worth knowing

If testosterone is low and LH is **high**, the testicles are the problem. If testosterone is low and LH is **low or inappropriately normal**, the problem is upstream — in the pituitary or hypothalamus — and prolactin should be measured. This single distinction is what separates a proper hormonal workup from a superficial one.

### What raises prolactin

- **Prolactinoma** — a benign pituitary tumour, and the most important cause to exclude. Large ones can press on the optic chiasm and cause visual field loss.
- **Medications** — antipsychotics (especially risperidone and haloperidol), metoclopramide, domperidone, some antidepressants, verapamil, opioids.
- **Hypothyroidism** — which is why the two tests belong together.
- **Chronic kidney disease** and cirrhosis.
- **Stress, recent nipple stimulation, or a recent seizure** — all can raise a single reading transiently, which is why abnormal results are repeated.

> **When to escalate quickly**
>
> Headaches with peripheral vision loss, or a markedly raised prolactin, warrant prompt endocrine referral and pituitary imaging. Do not sit on those symptoms.

## What treatment looks like

1. **Confirm the abnormality** — thyroid and prolactin results are repeated before acting, since transient elevations are common.
2. **Identify the cause** — medication review first, then imaging where a pituitary cause is suspected.
3. **Treat the underlying condition** — thyroid replacement or antithyroid treatment; dopamine agonists such as cabergoline for a prolactinoma, which often shrink the tumour as well as normalising the hormone.
4. **Re-check testosterone afterwards.** Correcting prolactin frequently restores testosterone without any need for replacement — which matters a great deal if you want children, since [testosterone therapy suppresses fertility](https://www.edtreatmentguides.com/treatments/testosterone-therapy).
5. **Give it time.** Sexual symptoms typically improve over weeks to months once hormone levels stabilise, not overnight.

> **Do not accept testosterone replacement without this workup**
>
> Prescribing testosterone to a man whose real problem is a prolactinoma treats the number and leaves the tumour. If your testosterone is low, ask what your LH and prolactin were before you start lifelong replacement.

## Frequently asked questions

### Should thyroid be checked for erectile dysfunction?

It is inexpensive, and both underactive and overactive thyroid are associated with sexual dysfunction and are reversible. It is reasonable to request it, especially with any general thyroid symptoms.

### What does high prolactin mean?

It suppresses testosterone production, causing low libido and erectile dysfunction. Causes include medications, an underactive thyroid, kidney disease and a benign pituitary tumour — which needs excluding.

### Will treating these fix my ED?

Frequently, where they are the main driver, though improvement takes weeks to months. They are among the more genuinely reversible causes.

### Can antidepressants raise prolactin?

Some can, and antipsychotics commonly do. Never stop a psychiatric medication on your own — raise it with your prescriber, since alternatives often exist.

## Sources

- Endocrine Society. [Testosterone Therapy in Men With Hypogonadism — clinical practice guideline](https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy) (2018)
- American Urological Association. [Testosterone Deficiency: AUA Guideline](https://www.auanet.org/guidelines-and-quality/guidelines/testosterone-deficiency-guideline) (2018)
- MedlinePlus (National Library of Medicine). [Drugs, Herbs and Supplements](https://medlineplus.gov/druginformation.html)
- National Institute of Diabetes and Digestive and Kidney Diseases. [Definition & Facts for Erectile Dysfunction](https://www.niddk.nih.gov/health-information/urologic-diseases/erectile-dysfunction)

## Related pages

- [Low Testosterone and ED: Sorting Signal From Marketing](https://www.edtreatmentguides.com/causes/low-testosterone)
- [Testosterone Therapy for ED: When It Helps and When It Does Not](https://www.edtreatmentguides.com/treatments/testosterone-therapy)
- [Medications That Cause ED — and What to Do About It](https://www.edtreatmentguides.com/causes/medication-side-effects)
- [ED Symptoms and How It Is Diagnosed](https://www.edtreatmentguides.com/guides/symptoms-and-diagnosis)

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_This page is general health information, not medical advice. It cannot account for your own history, medications or risk factors. Talk to a licensed clinician before starting, stopping or changing any treatment._

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