Hydrochlorothiazide (HCTZ, Microzide)
A first-line thiazide diuretic (“water pill”) for high blood pressure. Inexpensive and effective, but watch your electrolytes and sun exposure.
What it's used for
Hypertension (high blood pressure) as first-line or add-on therapy, and mild fluid retention (edema) from heart failure or kidney disease. Often combined with other blood pressure drugs in a single pill (e.g., with losartan, lisinopril, or valsartan).
Typical dosing (adults)
- Blood pressure: 12.5–25 mg once daily (higher doses rarely more effective but cause more side effects).
- Edema: 25–100 mg daily in one or two doses.
- Take in the morning to avoid nighttime trips to the bathroom.
Key interactions
- Lithium: major — HCTZ reduces lithium excretion, raising levels to potentially toxic range.
- Digoxin: major — low potassium from HCTZ increases digoxin toxicity risk.
- NSAIDs (ibuprofen, naproxen): moderate — reduce the blood pressure-lowering effect and may worsen kidney function.
- Diabetes medications (insulin, sulfonylureas): moderate — HCTZ can raise blood sugar, potentially requiring dose adjustments.
- Other blood pressure medications: moderate — additive blood pressure lowering (usually intentional, but monitor for dizziness).
Common side effects
Increased urination (especially in first few days), low potassium (muscle cramps, weakness, irregular heartbeat), dizziness, elevated uric acid (gout flares), increased blood sugar. Photosensitivity — HCTZ makes your skin more sensitive to sunburn. Rare: low sodium, allergic reaction (contains a sulfonamide group).
Who should be cautious
- Gout (HCTZ raises uric acid levels and can trigger attacks).
- Diabetes (may worsen blood sugar control).
- Severe kidney disease (may be ineffective when GFR is very low).
- Sulfonamide allergy (cross-reactivity is debated but possible).
- Pregnancy (avoid, especially in later trimesters).
What to ask your pharmacist
- Should I eat extra potassium-rich foods (bananas, potatoes) or take a supplement?
- How often should I have my electrolytes checked?
- Do I need extra sun protection while on HCTZ?
- Can I take ibuprofen for a headache while on this medication?