Merck & Co
About Hydrochlorothiazide

This belongs to the group of medicines known as diuretics. Diuretics are often referred to as water tablets. Hydrochlorothiazide is used to treat hypertension (high blood pressure) and edema (fluid retention), often caused by heart failure.

Before Taking Hydrochlorothiazide

Before taking hydrochlorothiazide make sure your doctor or pharmacist knows:

  • if you are pregnant, trying for a baby or breast-feeding
  • if you suffer from liver or kidney problems
  • if you suffer from Addison's disease, diabetes, gout, porphyria (a blood disorder) or systemic lupus erythematosus (SLE)
  • if you suffer from prostate problems or have problems urinating (passing water)
  • if you have ever had an allergic reaction to this or any other medicine
  • if you are taking any other medicines, including those available to buy without a prescription, herbal and complementary medicines

How to Take Hydrochlorothiazide

Take hydrochlorothiazide exactly as directed by your doctor.

Always read the manufacturer's information leaflet, if possible, before beginning treatment.

Hydrochlorothiazide will make you urinate (pass water) more often, so your doctor or pharmacist will usually advise you to take your dose in the morning so as not to disturb your sleep. If you take more than one dose per day, take the last dose before 6pm in the evening.

Never take more than the prescribed dose. If you suspect that you or someone else has taken an overdose of hydrochlorothiazide contact your doctor or go to the accident and emergency department of your local hospital at once. Always take the container with you, if possible, even if it is empty.

Hydrochlorothiazide is for you. Never give it to others, even if their condition appears to be the same as yours.

Getting the most from your treatment

  • Keep your regular appointments with your doctor so that your progress can be monitored.
  • Before taking any 'over-the-counter' medicines, check with your pharmacist which medicines are safe for you to take alongside hydrochlorothiazide.
  • Avoid excessive consumption of alcohol. Too much alcohol can cause a big drop in blood pressure and may lead to fainting.
  • Many patients with high blood pressure do not feel unwell, but left untreated it can damage the heart, arteries and blood vessels resulting in a stroke, heart failure or kidney failure. It is very important to take hydrochlorothiazide exactly as directed by your doctor and not to stop taking it without speaking to your doctor first, even if you feel quite well.
  • It is important to follow any dietary advice that you have been given by your doctor. If you are overweight, your doctor may want you to follow a weight reducing diet.
  • Diuretics help you to lose water. On occasions you may lose too much and become dehydrated, leaving you feeling thirsty and your skin looking and feeling dry.
  • Hydrochlorothiazide may cause dry mouth. If you experience this try chewing sugar-free gum, sucking sugar-free sweets or pieces of ice. If dry mouth becomes too troublesome, discuss the problem with your doctor or pharmacist.
  • Hydrochlorothiazide may cause you to experience fainting or dizziness when getting up from a lying or sitting position. Getting up slowly should help. If this becomes too troublesome discuss the problem with your doctor or pharmacist.
  • Before having any kind of surgery, including dental or emergency treatment, tell the surgeon, dentist or doctor that you are taking hydrochlorothiazide.
  • If you have diabetes hydrochlorothiazide may affect your blood sugar levels. Test your urine or blood regularly and report any extreme changes to your doctor.
  • Hydrochlorothiazide may cause your skin to become more sensitive to sunlight than it is usually. Try to avoid bright sunlight and sunbeds or use a sun cream higher than factor 15 until you know how your skin reacts.

Side Effects:

Along with their useful effects all medicines can cause unwanted side effects. These usually improve as your body adjusts to the new medicine. Speak to your doctor or pharmacist if any of the following side effects continue or become troublesome:

Tummy upset, sexual problems, gout (pain and stiffness in the joints), light-headedness, dry mouth, muscle cramps or skin rashes.

Severe nausea, vomiting or diarrhoea may cause you to lose additional water and potassium.

Signs of excessive potassium loss are dryness of the mouth, increased thirst, irregular heartbeat, mood changes, muscle cramps or pain, nausea (feeling sick), vomiting (being sick), unusual tiredness or weakness, a weak pulse or loss of appetite.

Signs of excessive sodium loss are confusion, convulsions (fits), difficulty concentrating, irritability, muscle cramps and unusual tiredness or weakness. If you think you may be suffering from a lack of potassium or sodium or if you experience any other worrying side effects, which you think may be due to this medicine, discuss them with your doctor or pharmacist.

How to store Hydrochlorothiazide

  • Keep out of reach of children.
  • Store in a cool, dry place, away from direct light and heat.
  • Never keep out of date or unwanted medicines. Discard them safely out of the reach of children or take them to your local pharmacist who will dispose of unwanted medicines for you.