Meds and you

Updated 11 February 2013


Hydrochlorothiazide is a diuretic drug used to treat congestive heart failure.


(Hydrochlorothiazide is also known as HCTZ)

Hydrochlorothiazide is the active ingredient of Hexazide and Ridaq.

Hydrochlorothiazide is also one of multiple active ingredients found in Accumax Co, Accuretic, Adco-Quinaretic, Adco-Retic, Amiloretic, Betaretic, Capozide, Captoretic, Cibadrex, Co-Diovan, Co-Micardis, Co-Renitec, Co-Tareg, Coaprovel, Cozaar Comp, Dyazide, Enap-Co, Fortzaar, Hexal-Lisinopril Co, Hexaretic, Inhibace Plus, Lisoretic, Lisozide, Moducren, Moduretic, Monozide, Pharmapress Co, Renezide, Sandoz Co-Amilozide, Sandoz Co-Triamterzide, Servatrin, Teveten Plus, Urirex K, Zapto-Co, Zestoretic, Zestozide, Zetomax Co and Ziak.

General information

Hydrochlorothiazide is a diuretic drug used to treat congestive heart failure (a condition where the heart battles to cope with its workload) and mild to moderately high blood pressure.

It is not a cure for high blood pressure, but is effective in keeping it under control. For it to be effective, you must take it regularly. High blood pressure declines slowly and it may take a few weeks for hydrochlorothiazide to reach its full effect. Keep taking this medicine during this period, even if you are feeling better or fail to notice any improvement.

The first couple of doses may cause a sudden drop in blood pressure that may cause dizziness or blackouts when you suddenly get up. It is therefore advised to be resting when starting treatment and to lie down for 2 hours afterwards.

Hydrochlorothiazide can be used on its own in treating mild cases of high blood pressure, or in combination with other medicines when high blood pressure is more severe.

Hydrochlorothiazide removes excess fluid from the body, thereby reducing oedema (an accumulation of excessive amounts of fluid in body tissue, resulting in swelling). Oedema usually occurs due to conditions such as congestive heart failure, kidney disorders and premenstrual syndrome.

The diuretic should be taken in the morning to prevent additional night-time visits to the toilet. It is possible that you may produce a larger volume of urine at the start of treatment with hydrochlorothiazide. Be aware of where your nearest ablution facilities are if you are away from home!

Hydrochlorothiazide enhances the excretion of potassium from your body and may warrant a potassium-rich diet (good sources are bananas or tomatoes), or even the use of a potassium supplement.

A low-sodium diet is furthermore advised as this may diminish potassium loss and also lower the dosage requirements for this drug.

How does hydrochlorothiazide work?

A diuretic such as hydrochlorothiazide reduces the overall fluid volume in the body, thereby reducing pressure within blood vessels.

Fast facts

Drug schedule: schedule 3

Available as: hydrochlorothiazide is available as tablets

What does it do? lowers blood pressure and reduces fluid volume in the body

Overdose risk: low

Dependence risk: low

Is hydrochlorothiazide available as a generic? yes

Is hydrochlorothiazide available on prescription only? yes

User information

Onset of effect: within 2 hours

Duration of action: up to 12 hours

Dietary advice: hydrochlorothiazide enhances the excretion of potassium from the body and may warrant a potassium-rich diet containing foods such as bananas or tomatoes

Stopping this medicine: it may be dangerous to discontinue the use of this drug abruptly as symptoms of the condition may recur; don't discontinue this drug without speaking to your doctor

Prolonged use: prolonged use may result in an electrolyte disturbance; kidney function may also need to be evaluated periodically

Special precautions

Consult your doctor before using this drug if:

  • you have kidney or liver disease
  • you have known low blood levels of potassium or high blood levels of calcium
  • you have gout
  • you have diabetes
  • you have Addison's disease
  • you have systemic lupus erythematosus
  • you are taking other medication

Pregnancy: avoid. Potential risk to the foetus has been reported. Consult your doctor before use, or if you are planning to fall pregnant.

Breastfeeding: avoid. This medication is passed through breast milk and may affect your baby adversely. Consult your doctor before use.

Porphyria: this medication is safe to use.

Infants and children : if used in children, the dose must be determined by a paediatrician.

Elderly: caution is advised in the elderly as adverse effects may be more likely.

Driving and hazardous work: caution is advised as use of this medication may lead to dizziness and light-headedness. Avoid such activities until you know how this medication affects you.

Alcohol: avoid concomitant use of alcohol with this medication.

Possible side effects

Side effect


Consult your doctor



Only if severe

In all cases

muscle cramps or pain












thirst/ dry mouth






loss of appetite



erectile dysfunction






increased blood sugar



skin rash/itch



swelling of mouth/ difficulty breathing



unusual bleeding and bruising




Drug interactions

ACE inhibitor drugs

increased dizziness at start of treatment

alcohol, barbiturates

increased dizziness at start of treatment

allopurinol, tetracycline antibiotics

increased risk of hydrochlorothiazide toxicity


reduced absorption of hydrochlorothiazide


reduced diuretic effect/ risk of potassium depletion


increased risk of toxicity in case of potassium depletion

terfenadine, sotalol, pimozide

risk of heart rhythm disturbance


risk of lithium toxicity

non-steroidal anti-inflammatory drugs

reduced diuretic effect/ increased risk of kidney damage

oral anti-diabetic drugs

blood sugar lowering effect may be reduced

co-trimoxazole, trimethoprim

reduced sodium levels in body

vitamin D

increased risk of high calcium blood levels

Disease interactions

Consult your doctor before using this drug if you have kidney or liver disease, gout, diabetes, Addison’s disease or if you have systemic lupus erythematosus.

Overdose action

A small overdose is no cause for concern. In case of intentional large overdose, seek emergency medical attention.

Recommended dosage


For high blood pressure: 12.5-25mg/day

For fluid retention: 25-100mg in divided doses

Children: The dose must be determined by a paediatrician

Interesting fact

Thiazide diuretics such as hydrochlorothiazide are also used in the treatment of osteoporosis. These diuretics decrease mineral bone loss by promoting calcium retention in the kidneys.


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