By the Medsmingle Team · Updated 13 November 2026
This is a prescription medicine. Only take it if it has been prescribed for you after a medical assessment, and follow your doctor’s and pharmacist’s instructions.
Hydrochlorothiazide (HCTZ) is a thiazide diuretic (“water pill”) used for high blood pressure and fluid retention. It’s often combined with other blood pressure medicines such as losartan or lisinopril.
How to take it
- Usually once a day, in the morning, so you aren’t up at night to pee
- Common doses are 12.5 to 25 mg
Side effects
- Peeing more often, especially at first
- Dizziness or light-headedness
- Low potassium or sodium (cramps, weakness, confusion)
- Raised blood sugar and uric acid; can trigger gout
- Increased sun sensitivity
Skin cancer advice
Hydrochlorothiazide is associated with a small increased risk of non-melanoma skin cancer. Do not stop prescribed treatment on your own. Use sunscreen, cover up, and check your skin regularly.
Get urgent help for
- Sudden eye pain or reduced vision (a rare eye reaction)
- Severe rash, fainting or confusion
Interactions
- Lithium (levels can rise)
- NSAIDs reduce its effect
- Diabetes medicines may need adjusting
Frequently asked questions
Do I need potassium supplements?
Only if a blood test shows low potassium and your doctor advises it.
For questions about a prescription or symptoms, speak with your own doctor or pharmacist. For website enquiries, contact our team.
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Medsmingle (medsmingle.com) shares clear, plain-English information on medicines and everyday health. Explore more health guides and the latest articles, read about us, or contact our team with a question.
General information only. It isn’t a substitute for advice from your doctor or pharmacist.
Source and further reading
MedlinePlus patient medicine information. This overview does not list every warning or interaction.
