Excessive Thirst: Causes and When to Worry

Short answer: Excessive thirst means drinking much more than usual, feeling thirsty again soon after drinking, or needing more than about 3 liters (100 ounces) a day without heat or exercise to explain it. The medical term is polydipsia. The most common causes are simple: too little water, salty food, alcohol, hot weather and some medicines. Diabetes is the most important cause to rule out, but it is far from the only one. If you are always thirsty and your sugar tests are normal, there are other clear tests to ask for.

Excessive thirst is not the same as heat stroke. Heat stroke happens in hot weather or during heavy exertion and comes with a very high body temperature, hot skin, confusion and sometimes collapse. It is a medical emergency: call 911 and cool the person right away. The thirst described in this article is ongoing and happens in ordinary conditions.

Dry mouth or real thirst?

A dry mouth makes you want to sip; real thirst makes you want to drink a lot. A dry mouth usually comes from medicines, mouth breathing or anxiety. Real, lasting thirst means the body is short of water or losing it, often through the urine. If your thirst is worst at night, our guide why am I so thirsty at night? covers the night-time causes.

Common causes of excessive thirst

• Not drinking enough during the day, or losing fluid through heat, exercise, fever, vomiting or diarrhea.
• Salty or spicy food, and alcohol, which makes the body lose water.
• Medicines: water pills, lithium, some diabetes medicines, and medicines that dry the mouth, such as some bladder, allergy, depression and psychiatric medicines. Our guide to oxybutynin side effects covers a common example.
• Diabetes. High blood sugar pulls water into the urine, causing thirst, frequent urination and often tiredness. Our guide to nocturia and diabetes explains the link.
• Pregnancy, when the body’s fluid needs rise.

Always thirsty but not diabetic?

A normal sugar test rules out one cause, not all of them. Other possibilities include:

• Diabetes insipidus. Despite the name, it has nothing to do with blood sugar. A hormone problem stops the kidneys from saving water, so large amounts of very pale urine are passed day and night, with intense thirst.
• High blood calcium, often from overactive parathyroid glands, too much calcium or vitamin D from supplements, or, less often, other illnesses. It also causes tiredness, constipation and frequent urination.
• Low blood potassium, sometimes from water pills, vomiting or diarrhea.
• Kidney problems that reduce the kidneys’ ability to concentrate urine.
• An overactive thyroid, which speeds up the body and increases fluid loss.
• The habit cycle. Drinking large amounts out of habit keeps the urine dilute, the body adjusts, and thirst returns sooner. Cutting back gradually often settles it.
• Anxiety and stress, which dry the mouth and can drive frequent sipping. Rarely, an urge to drink large amounts of water is linked to a mental-health condition.

Tests to ask your doctor about

If thirst has lasted more than a couple of weeks without a clear reason, these simple tests usually find or rule out the main causes:

1. Blood sugar: a fasting glucose and an A1C test.
2. Blood salts: sodium, potassium and calcium.
3. Kidney function blood tests.
4. A urine test, including how concentrated the urine is.
5. Thyroid function, if there are other signs such as weight loss or a racing heart.
6. A medicine review, including supplements.

It helps to bring a two- or three-day record of how much you drink and how often you pass urine. If diabetes insipidus is suspected, a specialist may arrange further tests.

The traditional Chinese medicine view

Classical Chinese medicine described a “wasting and thirsting” disorder, Xiao Ke, more than two thousand years ago: great thirst, great hunger and frequent urination with weight loss, closely matching what we now call diabetes. Traditional texts divided it into three parts: thirst linked to the Lung, hunger to the Stomach, and urination to the Kidney, all driven by deficient Yin and internal heat. Ongoing thirst with dryness, warmth and restlessness is also a classic sign of Yin deficiency, the counterpart of the cold pattern described in our guide to Kidney Yang deficiency.

The Shang Han Lun (Treatise on Cold Damage, around 200 CE) also describes a thirst that is not caused by heat. In Clause 71, a person is thirsty and drinks, yet urine is scant and there is only mild fever. The classical formula for this pattern, Wu Ling San (Five-Ingredient Powder with Poria), works by helping the body move and transform water rather than by cooling. In this view, the body is not short of water; the water is simply not reaching where it is needed. This is different from the great thirst of summer heat or heat stroke, which the classics treat in a separate way.

These are traditional descriptions. Oral herbal formulas should only be taken under a qualified practitioner, and they do not replace the medical tests above.

Older adults: often the opposite problem

With age, the sense of thirst usually becomes weaker, not stronger. Many older adults drink too little rather than too much. Our guide to signs of dehydration in older adults explains what to watch for. New, strong thirst in an older person should always be checked.

Questions about excessive thirst

What is the medical term for excessive thirst?

Polydipsia. Passing large amounts of urine is called polyuria; the two often occur together.

Can stress make you thirsty?

Yes. Stress and anxiety can dry the mouth and lead to frequent sipping. If thirst eases when you are calm or busy, stress may be part of it, but other causes are still worth ruling out.

Why am I still thirsty after drinking water?

If thirst returns soon after drinking, the body may be losing water through the urine, as with high blood sugar or diabetes insipidus, or the mouth may be dry from medicines or mouth breathing. Thirst that water does not settle deserves a doctor’s visit.

Independent sources

MedlinePlus: Thirst, excessive

General education; this article does not replace advice from your own doctor.