dry mouth

A dry mouth is not a diagnosis in itself. It is a symptom and there are various causes which include:

Medication. Various drugs can cause a dry mouth as a side-effect. For example, tricyclic antidepressants, antihistamines, antimuscarinic drugs, some antiepileptic drugs, some antipsychotics, betablockers, and diuretics (‘water tablets’). Many of these drugs cause a dry mouth by affecting the salivary glands which reduce the amount of saliva that these glands make.
Radiotherapy to the head or neck. The radiotherapy can damage the salivary glands.
Mouth breathing – which can be due to a blocked nose or other causes.
Anxiety.
Dehydration (low body fluid). This may occur for many reasons, but you will usually be quite ill with fever or other symptoms if you are dehydrated.
Sjögren’s syndrome. This is a condition which can affect various parts of the body, including the joints (which can cause arthritis), the salivary glands (which can cause a dry mouth), and the tear glands (which can cause dry eyes).
What are the treatments for a dry mouth?
If possible, treat any underlying cause
In some cases, it may be possible to treat the underlying cause. For example:

If a drug is causing the dry mouth as a side-effect, it may be possible to change to a different drug, or to reduce the dose.
Dehydration, a blocked nose, and anxiety can often be treated.
Practical measures
Whatever the cause, the following will often help:

Take frequent sips or sprays of cold water. Always have a glass of water next to you when you go to bed.
Suck ice-cubes.
Sugar-free chewing gum is often helpful.
Eating pineapple chunks or partly frozen melon is often soothing and helpful.
Some people find that it helps to suck boiled sweets. (But, sugary or acid sweets may not be good for your teeth.)
Consider reducing or cutting out caffeine and alcohol which have a diuretic effect. (This means that they can make you pass out more urine, which can be dehydrating.) Caffeine occurs in tea, coffee, cola and other drinks. It is also part of some drugs.
You can apply petroleum jelly to your lips to prevent drying and cracking.
Artificial saliva
If the above measures are not adequate, then your doctor may prescribe a spray, gel or lozenge which acts as a substitute for saliva. Each dose only lasts a short time and so they need to be used frequently. Some people find artificial saliva products more helpful than others.

Saliva stimulants
In some cases of dry mouth, the saliva glands are only partially affected and can be stimulated to make more saliva:

Chewing sugar-free gum can help to increase the production and flow of saliva.
Pilocarpine is a drug which can stimulate salivary glands to make more saliva. It may be prescribed if other measures have not helped much.
Pilocarpine usually works well and quickly in most people with a dry mouth caused by a medication side-effect.
About half of people with radiotherapy-induced dry mouth respond to treatment with pilocarpine. In these people it may take several weeks, even up to three months, before the drug starts to work. So, it is worth persevering with treatment if it does not seem to be working at first.
Pilocarpine can cause side-effects in some people, such as sweating, dizziness, runny nose, blurred vision and frequent trips to pass urine. Side-effects tend to become less troublesome in time as your body becomes used to to this drug. So, a doctor may suggest a low dose at first and to take this for a while until any side-effects have eased. The dose may then be gradually increased with the aim of getting maximum benefit but with minimum side-effects.
Pilocarpine should not normally be used if you have asthma, chronic obstructive pulmonary disease (COPD), bradycardia (slow heart rate), bowel obstruction, or angle-closure glaucoma