Feeling thirsty all the time and for no good reason isn't normal and should be investigated by your GP.
Normally, feeling thirsty is the brain's way of warning that you're dehydrated because you're not drinking the amount of fluid your body needs. You can soon quench your thirst and restore the fluid balance in your body after having a drink.
If thirst is excessive and persistent, it could be a sign of diabetes or another underlying health condition (see below).
Doctors often refer to abnormal thirst as 'polydipsia'.
Points to consider
It's worth thinking about what you've been eating and drinking recently. Eating more salty or spicy foods than normal can cause a sudden increase in thirst.
Thirst can also be caused by losing excessive amounts of water from the body. This can happen after:
intense exercise where water is lost through sweating
diarrhoea and vomiting
A dry mouth or excessive thirst can sometimes be a side effect of certain types of medication, such as antidepressants, antihistamines or diuretics (water tablets). These medicines can affect the salivary glands, leading to a reduction in the amount of saliva they produce.
If a particular medicine is causing your dry mouth, it may be possible to change to a different medicine or reduce your dose. Speak to your GP about this.
In women, feeling thirsty can also be one of the symptoms of pregnancy. This is because of hormonal changes that occur during pregnancy.
When to see your GP
You should see your GP if you:
feel thirsty all the time for no apparent reason
feel thirsty all of the time and you also have other symptoms, such as extreme tiredness (fatigue) or passing a lot of urine
Your GP will probably carry out a blood glucose test to see whether you have diabetes.
As well as feeling thirsty, people with diabetes usually feel very tired and need to go to the toilet a lot, particularly at night.
If you have diabetes, your body will be unable to break down glucose into energy. This is because either the body doesn't produce enough of the hormone insulin to move the glucose, or the insulin that is produced doesn't work properly.
Other causes of thirst
There are also many other potential causes of a dry mouth or severe thirst. These include:
sickle cell anaemia – an inherited blood disorder
diabetic ketoacidosis – a dangerous complication of diabetes caused by a lack of insulin in the body
Sjogren's syndrome – where the body’s immune system attacks glands that secrete fluid, such as the tear and saliva glands
psychogenic polydipsia – where a person with a mental health condition, such as schizophrenia, drinks excessive amounts of water that can't be excreted (got rid of) by the kidneys
Any condition that leads to dehydration will cause thirst.
Hot weather and exercise
It's very important to drink plenty of water or other drinks (non-alcoholic) during hot weather and while exercising or doing other types of strenuous physical activity.
Remember, you need to take on board extra fluid while exercising in hot conditions to avoid becoming dehydrated.
It's important to drink plenty of fluids, particularly in hot weather and when exercising
Some people complain of being thirsty when they actually have a dry mouth. It's important to know the difference between the two because they can have completely different causes.
If your mouth is permanently dry, the cause is more likely to be anxiety or certain medications, including some types of antidepressants and hyoscine.
Dry mouth at night and first thing in the morning may be due to having a blocked nose and breathing through your mouth while asleep.