Hydrochlorothiazide

What it is

Hydrochlorothiazide is a thiazide diuretic. It blocks the sodium-chloride cotransporter in the distal tubule of the kidney, increasing the excretion of sodium and water and, over time, lowering vascular resistance. It is used for high blood pressure and for fluid retention.

Used for

• Hypertension
• Oedema

What to know while taking it

Food makes no difference, but it belongs to the morning, because the diuretic effect otherwise interrupts sleep. It depletes potassium, magnesium and zinc while tending to retain calcium, so potassium, sodium, calcium, uric acid and glucose are the usual laboratory checks. Uric acid and blood sugar can drift upward on this class, which matters in gout and in diabetes. Enough fluid should be taken, and the drug increases sensitivity to sunlight, so strong sun and sunbeds are worth avoiding.

When to see a doctor

Cramps, unusual weakness, palpitations, confusion or fainting suggest a disturbed potassium or sodium level and warrant seeing a doctor. So do a sudden painful swollen joint, a persistent rash after sun exposure, or vomiting and diarrhoea that make dehydration likely.

Worth knowing

• Can lower potassium
• Avoid strong sun
• Drink enough water

Markers to watch

• Potassium
• Sodium
• Uric acid
• Glucose
• Calcium, total

Nutrients affected

• potassium — depleted by (Potassium)
• magnesium — depleted by (Glucose, HOMA-IR, Magnesium)
• zinc — depleted by (Free T3, Testosterone, TSH)