Hydrochlorothiazide vs furosemide (Lasix): diuretics compared
Hydrochlorothiazide and furosemide (Lasix) are both water pills, but they are used differently. Hydrochlorothiazide is a mild, long-acting diuretic mainly for high blood pressure; furosemide is a strong, short-acting diuretic for fluid buildup from heart, kidney or liver disease.
Updated October 4, 2026
At a glance
- Strength
- Hydrochlorothiazide
- Mild
- Furosemide
- Strong
- Main use
- Hydrochlorothiazide
- High blood pressure
- Furosemide
- Fluid buildup (edema) from heart, kidney or liver disease
- Timing of effect
- Hydrochlorothiazide
- Gentle, through the day
- Furosemide
- Strong urination within about an hour, lasting several hours
- Works with poor kidney function
- Hydrochlorothiazide
- Less effective when kidney function is low
- Furosemide
- Yes
- Generic
- Hydrochlorothiazide
- Yes
- Furosemide
- Yes
Hydrochlorothiazide a thiazide diuretic | Furosemide Lasix, a loop diuretic | |
|---|---|---|
| Strength | Mild | Strong |
| Main use | High blood pressure | Fluid buildup (edema) from heart, kidney or liver disease |
| Timing of effect | Gentle, through the day | Strong urination within about an hour, lasting several hours |
| Works with poor kidney function | Less effective when kidney function is low | Yes |
| Generic | Yes | Yes |
Different jobs
Hydrochlorothiazide is a first-line blood pressure medicine because its mild, steady effect lowers pressure over time without large swings in fluid. Furosemide removes a lot of fluid quickly, which is what swollen legs or fluid on the lungs from heart failure need, but it is not usually used for blood pressure alone.
Effects on blood tests
Both lower potassium and sodium and can cause dehydration, so blood tests are checked. Hydrochlorothiazide also tends to raise calcium, blood sugar and uric acid, which can trigger gout. Furosemide lowers calcium and, at high doses, can affect hearing, especially with certain antibiotics.
Practical tips
Take either in the morning, with any second furosemide dose by early afternoon, so you are not up at night. Keep drinking enough unless you have been told to limit fluids, and report dizziness, muscle cramps, extreme thirst or very little urine. Hydrochlorothiazide makes skin burn more easily in the sun and long-term use is linked to some skin cancers, so use sun protection.
Shared cautions
Anti-inflammatories blunt the effect of both, and both raise lithium levels. People with heart failure who take furosemide are often asked to weigh themselves daily and report sudden gains.
Cost
Both are among the least expensive generics.
Missed doses
Take a missed dose when you remember, but avoid taking it in the evening, which can keep you up at night; if it is nearly time for the next dose, skip it. Never double up.
Questions for your prescriber
- Is a diuretic the right choice for my blood pressure or swelling?
- How often should my potassium and kidney function be checked?
- What weight change should prompt me to call?
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Sources
Written by the Script Unlock editorial team from the sources above. It is general information, not advice for you or your pet; your prescriber decides which medicine is right.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.