Thirst

Feeling thirsty all the time, with no good reason, isn't normal. You should see a doctor and have it looked into.

Thirst is usually just your brain's way of telling you that you're dehydrated because you haven't been drinking enough fluid. But thirst that is excessive and doesn't go away (doctors call it polydipsia) could be a sign of an underlying problem, such as diabetes.

Most of the time, you feel thirsty because you're not drinking as much fluid as your body needs. You may have been sweating heavily, or you may have lost fluid through diarrhoea and vomiting.

A drink will soon quench your thirst and bring the fluid balance in your body back to normal, as long as you then keep yourself well hydrated.

Staying well hydrated matters most in hot weather, while you're exercising, and when you're unwell with vomiting and diarrhoea.

Sometimes thirst has a very simple cause, like something you ate a short while ago. A salty or spicy meal or snack can make you feel thirsty quite suddenly.

If you feel thirsty all the time, it could be a sign of diabetes, particularly if you also have other symptoms such as needing to urinate often, extreme tiredness (fatigue) and weight loss you can't explain.

Diabetes is a lifelong condition that makes it difficult to control the level of sugar (glucose) in your blood. When glucose levels are high, your kidneys have to make more urine to help pass the glucose out of your body. That can leave you feeling thirsty, because your brain is telling you to drink more to make up for the fluids you've lost.

If you feel thirsty all the time and have other symptoms, your doctor will probably do a blood glucose test to see whether you have diabetes.

Feeling thirsty, and needing to urinate more often than usual, are common in pregnancy and usually nothing to worry about.

Very occasionally, though, these problems can be a sign of gestational diabetes (a type of diabetes that affects women during pregnancy). If you're at risk, you should be screened for it as part of your antenatal care.

Feeling very thirsty can sometimes be a side effect of certain medicines. These include lithium, certain antipsychotics and diuretics (water tablets).

If you think one of your medicines is causing the thirst, it may be possible to switch you to a different medicine or lower your dose. Speak to your doctor about this.

Severe thirst can have many other causes. These include:

• diabetes insipidus, a condition caused by problems with a hormone that regulates the amount of fluid in the body
• diabetic ketoacidosis, a dangerous complication of diabetes caused by a lack of the hormone insulin in the body
• sickle cell anaemia, an inherited blood disorder
• psychogenic polydipsia, where a person with a mental health condition, such as schizophrenia, drinks excessive amounts of water that the kidneys can't excrete (get rid of)
• excessive bleeding