Medication Information Leaflet

​What is this medication for?

Hydrochlorothiazide belongs to a class of medications called Diuretics. It works on your kidneys to get rid of extra water and salts in your body. 

This medication is used to remove excess fluid from your body. This will decrease the pressure on the blood vessels and allow the heart to work less hard. Hence, it may also be used to treat high blood pressure.

How should I take/use this medication?

  • Do not stop taking your medication without first checking with your healthcare professional.
  • If you are taking one dose a day, take it in the morning. If you are taking the medication two times a day, take the second dose before 4pm so that you do not need to wake up often at night to pass urine.

What should I do if I forget to take/use this medication?

If you miss a dose, take the missed dose as soon as you remember. If it is almost time for your next dose, take only the usual dose. Do not double your dose or use extra medication to make up for the missed dose.  

What precautions should I take?

Inform your healthcare professional if: 
  • You are allergic to this medication or any of the other ingredients of this medication 
  • You are allergic to any other medications, especially sulfonamide medicines (e.g. Bactrim)
  • You are pregnant, planning to become pregnant, or breastfeeding
  • You have any problems with the way your kidneys work
  • You have gout 
  • You have lupus or history of lupus, an autoimmune disease where your body’s immune system attacks your own tissues and organs
  • You have ever been treated for skin cancer before, or are currently on any medications that suppress your immune system. 

What are some common side-effects of this medication?

Some side effects may include:
  • Passing urine more often, dry mouth, increased thirst
    • Too much water loss may result in dehydration. Inform your doctor if you are always feeling thirsty, tired, or you have muscle cramps. 
    • Drinking excessive amounts of water to replace your water loss or because you feel thirsty may lead to your heart condition becoming worse. Discuss with your healthcare professional about the amount of fluids you may take each day.
  • Dizziness and lightheadedness
    • This may occur especially when you get up quickly from lying or sitting down. Getting up slowly or changing posture slowly may help. Take a rest by sitting or lying down if you feel dizzy.
  • Affect your mineral levels in your blood
    • This medication may cause potassium loss. Inform your healthcare professional if you experience symptoms of excessive potassium loss such as weakness/ tiredness, muscle cramps, loss of appetite or irregular/ fast heart beat
  • More sensitive to sunlight, skin rash 
    • Avoid unnecessary sunlight exposure. Use sunblock, sunglasses or wear covered clothes to protect your skin and eyes from excessive sunlight exposure.
Inform your healthcare professional if these side effects do not go away and become bothersome to you.

What are some rare but serious side-effects that I need to seek medical advice immediately?

Very rarely, this medication may be linked to the increased risk of Non-melanoma skin cancer. Overseas studies involving Caucasians (fair skin) have shown that taking higher doses of this medication for long periods of time is linked to a very small risk of this skin cancer. The results of these studies cannot be directly applied to most of the Singaporean population as the skin types are very different. The risk of this skin cancer caused by this medication is likely to be lower in the local population
  • Inform your doctor immediately if you notice any new, abnormal skin lesions or unusual lumps or patches on your skin that do not heal or go away after a few weeks. 
  • Avoid standing under midday sun (11am to 4pm) and seek shade whenever possible
  • Take extra care by wearing long-sleeved clothes and applying sunblock to protect yourself from the sun.
The symptoms of a drug allergy include one or more of the following: 
  • Swollen face/eyes/lips/tongue
  • Difficulty in breathing
  • Itchy skin rashes over your whole body
If you experience any of these symptoms, you should stop your medication and see your healthcare professional immediately.

How should I store this medication?

Store in a cool and dry place, away from direct sunlight. Keep this medication away from children. Throw away all expired medications.

How should I throw away this medication safely?

Pack this medication into a black trash bag and seal it tightly before throwing into the rubbish chute or bin.

If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on July 2019


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