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Hydrochlorothiazide (HCT) is a thiazide diuretic (water tablet) that lowers blood pressure and is often used as a combination partner. Key points are taking it in the morning, regular electrolyte checks and consistent sun protection.
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Never stop or pause hydrochlorothiazide on your own. Stopping abruptly can cause your blood pressure to rise again – always discuss any changes with your GP practice. Hydrochlorothiazide (HCT for short, brand name Esidrix®) is a water tablet (diuretic) from the thiazide group. It lowers blood pressure by prompting the kidneys to excrete more water and salt. HCT is often prescribed as a fixed combination partner with other blood-pressure-lowering drugs in a single tablet.
| Property | Details |
|---|---|
| Active ingredient | Hydrochlorothiazide (HCT) |
| Brand name | Esidrix® |
| ATC code | C03AA03 |
| Drug class | Thiazide diuretic |
| Form | Tablets 12.5 / 25 mg (often as a combination product) |
| Intake | Once daily, in the morning |
| Standard dose | 12.5–25 mg/day |
| Monitoring | Regular blood tests (sodium, potassium) |
| Prescription required | Yes |
Hydrochlorothiazide acts directly in the kidneys. There it blocks a salt transporter in the kidney tubules, so that more sodium and water are excreted in the urine. This reduces the amount of fluid in the blood vessels, and with longer-term use the vessel walls also relax – both of which lower blood pressure.
That is why HCT is a first-line medication for high blood pressure. According to current guidelines it is rarely used alone; instead it is usually combined with an ACE inhibitor such as ramipril or a sartan such as candesartan – often in a single tablet. Unlike the stronger loop diuretic torasemide, HCT works more mildly and spread across the day.
The usual dose is 12.5 to 25 mg once daily, ideally in the morning. The reason: HCT is a diuretic and causes increased urination – if taken in the evening, you would need to go to the toilet more often during the night.
| Situation | Dose |
|---|---|
| Standard (high blood pressure) | 12.5–25 mg once/day in the morning |
| As a combination partner (e.g. with ramipril) | 12.5–25 mg in the fixed combination |
| Older people | Often a lower starting dose |
| Impaired kidney function | Effect wears off; possibly a different diuretic |
A missed dose is taken later the same morning as soon as you notice – but never take a double amount in one day. If you only notice late in the day, it is better to skip the dose to avoid needing to urinate during the night. The general rules for a missed dose are explained in the guide Forgot to take medication.
brite reliably reminds you of your morning HCT dose and documents it seamlessly.
Hydrochlorothiazide makes the skin more sensitive to light. With long-term use and a high cumulative dose, the risk of non-melanoma skin cancer (light skin cancer, especially squamous cell carcinoma) rises slightly. A European Direct Healthcare Professional Communication (Red Hand letter) has pointed this out. Important for context: the absolute risk remains low, and for many people the benefit of lowering blood pressure clearly outweighs it.
So you do not simply stop HCT, but instead protect yourself consistently against UV radiation. This is easy to put into practice in everyday life.
Most side effects of HCT are linked to the loss of water and salt. They are often dose-dependent and can be kept well under control through blood tests.
| Side effect | Frequency | What to do? |
|---|---|---|
| Increased urination | Very common | Take in the morning; normal at the start |
| Low potassium/sodium, muscle weakness, calf cramps | Common | Have blood values checked |
| Dizziness, circulatory weakness | Common | Stand up slowly; check blood pressure |
| Increased skin sensitivity to light | Uncommon | Consistent sun protection |
| Rise in blood sugar, uric acid (gout), blood lipids | Uncommon | Monitor lab values |
Because HCT flushes out water and salt, potassium and sodium in particular can drop too low in the blood. That is why regular blood tests are part of the treatment – especially in the first few weeks, when the dose is changed and during hot spells. In everyday life, make sure you drink enough but not excessively, and report persistent cramps, weakness or heart palpitations to your GP practice.
Some medications increase the salt loss or weaken the blood-pressure-lowering effect of HCT. Check combinations in the interaction check.
| Substance / medication | Interaction | Recommendation |
|---|---|---|
| NSAIDs (ibuprofen, diclofenac) | Blood-pressure effect falls, kidney under strain | Avoid; prefer paracetamol |
| Other diuretics, e.g. torasemide | Increased loss of salt and water | Only under medical supervision |
| Corticosteroids, laxatives | Additional potassium loss | Monitor potassium closely |
| Lithium | Lithium level rises (risk of toxicity) | Monitor levels; often avoid |
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