Pituitary Adenoma: The Tumour Treated With Tablets
The pituitary is about the size of a pea. It sits in a bony hollow behind the bridge of the nose, and it issues the instructions that control the thyroid, the adrenal glands, growth, reproduction and water balance. A gland that small holding that much authority means a small growth on it can produce an extraordinary range of consequences.
It also produces one of the more encouraging facts in cancer-adjacent medicine, which is worth stating immediately: these growths are almost always benign, and the commonest kind is treated with tablets that shrink it, rather than with surgery.
🎯 Problems arise in two entirely separate ways, and separating them explains everything else.
By what it makes. Some growths produce a hormone in excess. The symptoms then depend entirely on which hormone, which is why one condition can look like infertility, another like a change in facial appearance, and another like weight gain and diabetes.
By what it presses on. A larger growth pushes against neighbouring structures — most importantly the crossing point of the nerves from the eyes, which sits directly above — and it can also squash the healthy pituitary tissue around it, causing hormone deficiency alongside any excess.
A growth can do one, the other, or both, and the two produce completely different complaints.
🧪 The common one, and the good news
The most frequent hormone-producing pituitary growth releases prolactin, the hormone associated with milk production. Excess prolactin suppresses the reproductive hormones, and the consequences follow from that.
What makes it unusual among tumours is the treatment. Drugs that act on dopamine both normalise the hormone level and physically shrink the growth, often substantially, in the majority of people who take them. Surgery is reserved for the minority in whom tablets fail or cannot be tolerated.
Two are used. The newer one is generally better tolerated and is taken only twice a week; the older one is taken daily and causes more nausea, though it remains preferred in some situations including pregnancy planning. Both work best when started at a low dose and increased slowly, and both are usually taken with food at bedtime to reduce the nausea and light-headedness of the first weeks.
Treatment is often long-term, and in a proportion of people it can eventually be withdrawn after the level has stayed normal and the growth has shrunk or disappeared, with monitoring afterwards.
💊 Check the medicine list before assuming a tumour
⚠️ A raised prolactin level is far more often caused by medication than by a growth, and this is missed constantly.
Antipsychotic medicines are the leading cause. Several raise prolactin substantially, and the resulting symptoms — absent periods, milk production, reduced libido, breast enlargement in men — are frequently endured without being connected to the tablet, or attributed to the psychiatric illness itself. Some drugs in the class raise it far more than others, so switching is often possible.
Anti-sickness medicines such as metoclopramide and domperidone do the same, by the same dopamine-blocking mechanism described in the article on that drug family.
Also: some antidepressants, opioids, and verapamil. Alongside those, an underactive thyroid, kidney disease, pregnancy, chest wall injury and even the stress of the blood test itself can raise the level.
The practical order is: repeat the test properly, review every medicine, check thyroid function — and scan after that, not before. A scan ordered first will find an incidental harmless growth in a fair number of people and attribute the symptoms to it.
👥 Why men are diagnosed later
The same condition presents differently by sex, and the difference has consequences.
| In women | In men | |
|---|---|---|
| Typical signs | Periods becoming irregular or stopping, milk production without pregnancy, difficulty conceiving | Reduced libido, erectile difficulty, infertility, sometimes breast enlargement or milk production |
| How it is read | Noticed quickly, because a missed period is obvious and prompts investigation | Attributed to stress, age, relationship or mood — and rarely investigated hormonally |
| Time to diagnosis | Often within months | Frequently years |
| Size at diagnosis | Usually small | Usually large, so pressure effects are more likely |
| Other consequence | Low oestrogen over time reduces bone density | Low testosterone over time reduces bone density and muscle |
The practical message is for men. Persistent loss of libido or erectile difficulty is worth a hormone test rather than a prescription alone — not because it is usually a pituitary problem, but because when it is, the years spent not asking are what allow the growth to become large.
👁️ The vision loss people do not notice
When a growth extends upward it presses on the crossing point of the nerves from the eyes, and it does so in a characteristic way: the outer half of the visual field is lost on both sides.
The remarkable thing is how invisible this is to the person. Central vision stays sharp, reading is unaffected, and the brain fills in the missing edges. What people notice instead is bumping into door frames, missing objects to the side, difficulty parking, or failing the visual field part of a driving assessment. Some are told for months that their eyes are fine, because standard sight tests measure sharpness rather than field.
A simple self-check: cover one eye, look straight ahead at a fixed point, and have someone bring a finger in from the side at eye level. If it appears much later on the outer side than expected, that deserves a formal visual field test.
Vision loss from pressure is largely reversible if treated promptly and much less so once established, which is why it is treated with urgency rather than added to a waiting list.
📸 The one diagnosed by old photographs
A growth producing growth hormone in an adult causes acromegaly, and it is notorious for taking years to recognise — commonly seven to ten — for a simple reason: the changes are gradual, they affect appearance, and the people who see the person daily adapt to them without noticing.
What actually happens is that hands and feet enlarge. Rings stop fitting and are resized, then resized again. Shoe size increases in adulthood. The features coarsen, the jaw becomes more prominent, and the teeth begin to space out. Alongside that: increased sweating, headaches, carpal tunnel symptoms in both hands, joint pain, deepening voice, snoring and sleep apnoea, raised blood pressure and raised blood sugar.
The diagnostic tool that beats every examination is a photograph from ten or fifteen years ago placed beside a current one. The change is usually unmistakable, and it is invisible in the mirror.
Anyone whose ring size and shoe size have both increased in adulthood, particularly alongside carpal tunnel symptoms and snoring, has a reason to ask for the blood test. Treatment is usually surgical first, with medication where surgery does not fully control it, and correcting the excess reverses much of the metabolic damage even though skeletal changes remain.
☁️ Cortisol excess from above
A growth producing the hormone that instructs the adrenal glands drives cortisol excess, producing the picture described in the article on cortisol — weight gathering on the trunk and face with thinning limbs, wide purple stretch marks, easy bruising, thigh weakness, raised blood pressure and blood sugar, and mood disturbance.
The distinction that matters is that the commonest cause of that picture worldwide is not a growth at all but prescribed steroid medication. Establishing which is which comes first, and the tests to do it are specific.
🚨 The emergency
🔴 Bleeding into a pituitary growth is a medical emergency and can be the first sign that one exists. It produces a sudden severe headache reaching full intensity within minutes, often with vomiting, rapid loss or blurring of vision, double vision or a drooping eyelid, and sometimes confusion or collapse.
It is easily mistaken for other causes of sudden headache, and the reason it cannot wait is that the pituitary may stop producing cortisol abruptly — which is life-threatening on its own, quite apart from the pressure on the eyes.
Any headache reaching maximum intensity within a minute is an emergency regardless of cause. Adding sudden visual change or double vision makes it more urgent still.
🩹 When the gland underproduces
A large growth, or its treatment, can leave the pituitary unable to issue its instructions. The result is deficiency of whichever hormones are affected, and the symptoms are vague enough to be attributed to almost anything: exhaustion, weight change, cold intolerance, low mood, loss of libido, absent periods, and in some cases excessive thirst and urination.
One detail here is genuinely important and worth carrying away.
Where both cortisol and thyroid hormone need replacing, the cortisol must be started first. Thyroid hormone raises the body demand for cortisol, so giving it to someone whose cortisol production has failed can precipitate a dangerous collapse. This is a standard rule and it is occasionally got wrong, usually when thyroid results come back first and are acted on alone.
Anyone on long-term steroid replacement also needs the sick-day rules described in the cortisol article: during a feverish illness the dose typically has to increase, and vomiting means an injection is needed rather than a delay.
🔎 Found by accident
Small pituitary growths turn up regularly on scans performed for something else entirely, and this is common enough to have its own name. The great majority produce no hormone, cause no symptoms, and never grow to a size that matters.
Standard practice is hormone testing to confirm nothing is being overproduced or underproduced, a visual field check if the growth is near the nerves, and repeat imaging after an interval to confirm stability. Most require nothing further, and being told there is a growth on the pituitary is not, on its own, a reason for alarm.
| Type | First-line approach |
|---|---|
| Prolactin-producing | Tablets, which shrink it in most people. Surgery only if these fail |
| Growth hormone-producing | Surgery, with medication where control is incomplete |
| Cortisol-driving | Surgery, with medication and other options if it recurs |
| Non-functioning, small | Monitoring alone |
| Non-functioning, pressing on the nerves | Surgery, usually through the nose rather than open |
🩺 When to seek help
- Sudden severe headache with visual change or double vision — emergency
- Losing vision to the sides, bumping into things, or failing a visual field test — urgent
- Milk production without pregnancy or breastfeeding, in either sex
- Periods becoming irregular or stopping without explanation
- Persistent loss of libido or erectile difficulty in men — ask for hormone testing, not only treatment
- Ring and shoe size both increasing in adulthood, with carpal tunnel symptoms or new snoring
- A raised prolactin result — ask for the medication list to be reviewed and thyroid checked before any scan
- Symptoms on an antipsychotic — raise it, since some drugs in the class affect prolactin far less than others
- Fever or illness on steroid replacement — the dose needs increasing
- Being started on thyroid hormone with known pituitary disease — confirm cortisol has been assessed first
Treatment for raised prolactin is stocked as Dostinex (cabergoline) and Parlodel (bromocriptine). Both require a confirmed diagnosis and monitoring of hormone levels and tumour size, and both are started at a low dose and increased slowly to limit nausea and light-headedness. Where the cause turns out to be medication rather than a growth, the answer is a review of that medicine rather than either of these.
❓ Frequently asked questions
Is a pituitary adenoma cancer?
Almost never. These growths are benign in the great majority of cases — they do not spread, and malignant pituitary tumours are extremely rare. Problems come from what the growth produces or what it presses on, not from spread. Small ones found incidentally on scans are common and usually need nothing more than monitoring.
Can a brain tumour really be treated with tablets?
In this one case, yes, and it is unusual. Drugs acting on dopamine both normalise the prolactin level and physically shrink the growth, often substantially, in most people who take them. Surgery is reserved for those in whom tablets fail or cannot be tolerated. Treatment is usually long-term, and in some people it can eventually be withdrawn with monitoring.
My prolactin is high. Does that mean I have a tumour?
Usually not. Medication is a far more common cause — particularly antipsychotics, and anti-sickness drugs such as metoclopramide and domperidone. So can some antidepressants, opioids, verapamil, an underactive thyroid, kidney disease, pregnancy and even the stress of the blood test. The right order is to repeat the test, review every medicine and check thyroid function, and scan after that rather than before.
Why am I producing milk when I am not pregnant?
Because prolactin is raised, and that has several possible causes of which a pituitary growth is only one. Medication is commoner. It also happens in men, where it tends to be more alarming and is equally worth investigating. It is a symptom that deserves a blood test and a medication review rather than embarrassment, and the cause is usually treatable either way.
Why are men diagnosed so much later?
Because the symptoms are less specific. A missed period is obvious and prompts investigation, whereas reduced libido and erectile difficulty get attributed to stress, age, mood or the relationship, and are rarely investigated hormonally. The result is that men are typically diagnosed years later with larger growths, which makes pressure on the eye nerves more likely. Persistent symptoms deserve a hormone test.
How would I know if it was affecting my vision?
Probably not from the vision itself. The outer half of the field is lost on both sides while central vision stays sharp, so reading is unaffected and the brain fills in the edges. What people notice is bumping into door frames, missing things to the side, difficulty parking, or failing a driving field test. Standard sight tests measure sharpness, not field, so ask specifically for a field test.
What are the early signs of growth hormone excess?
Rings needing resizing and shoe size increasing in adulthood are the most useful, alongside coarsening features, teeth spacing out, increased sweating, carpal tunnel symptoms in both hands, new snoring or sleep apnoea, joint pain, and raised blood pressure or blood sugar. The best diagnostic tool is a photograph from ten or fifteen years ago beside a current one, since the change is gradual and invisible in the mirror.
What is a pituitary emergency?
Bleeding into the growth. It causes a sudden severe headache reaching full intensity within minutes, often with vomiting, rapid visual loss or blurring, double vision or a drooping eyelid, and sometimes confusion. It can be the first sign that a growth exists. It cannot wait, partly because the pituitary may stop producing cortisol abruptly, which is life-threatening on its own.
Why must steroid replacement come before thyroid hormone?
Because thyroid hormone raises the body demand for cortisol. Giving it to someone whose cortisol production has failed can precipitate a dangerous collapse. So where both need replacing, cortisol is started first. It is a standard rule and it is occasionally got wrong, usually when the thyroid result arrives first and is acted on in isolation.
A scan found a small one by accident. Should I worry?
Generally not. Small pituitary growths turn up regularly on scans done for other reasons, and the great majority produce no hormone, cause no symptoms and never grow to a size that matters. Standard practice is hormone testing, a visual field check if it sits near the nerves, and repeat imaging after an interval to confirm it is stable. Most need nothing further.
📑 Sources and editorial
- Epidemiology of pituitary adenomas, including incidental findings on imaging
- Guidelines on the diagnosis and management of hyperprolactinaemia and prolactinoma
- Evidence on dopamine agonist efficacy in normalising prolactin and reducing tumour volume, and on withdrawal after sustained remission
- Literature on drug-induced hyperprolactinaemia, including relative effects across antipsychotic agents
- Data on sex differences in presentation, tumour size and time to diagnosis
- Literature on chiasmal compression, bitemporal field loss and reversibility with prompt treatment
- Evidence on diagnostic delay in acromegaly and on characteristic clinical features
- Guidance on pituitary apoplexy recognition and emergency management
- Guidance on hormone replacement sequencing in hypopituitarism, including glucocorticoid before thyroid hormone
- Guidance on management of pituitary incidentalomas
- Related reading: cortisol and steroid effects, dopamine-blocking medicines, irregular cycles
- Related products: womens health category
- RXshop Editorial Team — reviewed by Daniel Kim, MD, Endocrinology
Medical Disclaimer: The information in this article is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek guidance from a qualified healthcare provider with any questions you may have regarding a medical condition, and before starting, stopping or changing any medication.