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Hydralazine for high blood pressure


Hydralazine is used to control high blood pressure (hypertension).

Treatment with hydralazine is usually long-term.

The most common side-effects are headaches and being aware of your heartbeat.

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About hydralazine

Type of medicine

A vasodilator antihypertensive medicine

Used for

The treatment of high blood pressure

Also called


Available as


Although many people with high blood pressure (hypertension) do not feel unwell, it is still important that high blood pressure be treated. If left untreated, high blood pressure is a risk factor that can increase your chance of developing heart disease, a stroke, and other serious conditions. Hydralazine will be prescribed alongside other medicines to control high blood pressure.

Hydralazine works by relaxing the muscles in the walls of your blood vessels. This means that your blood vessels widen, which reduces your blood pressure and allows blood and oxygen to circulate more freely around your body. Hydralazine will only be prescribed for you if other treatments are not suitable or effective, as it can increase the amount of water and salt in your body and can increase your heart rate. The other medicines you are prescribed to take alongside it will help to control these side-effects.

Hydralazine is occasionally prescribed by hospital doctors for other heart conditions. If you have been prescribed it for a reason other than high blood pressure, speak with your doctor if you have any questions about your treatment.

Before taking hydralazine

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking hydralazine it is important that your doctor knows:

  • If you have a condition called systemic lupus erythematosus. This is an inflammatory condition also called lupus, or SLE.

  • If you have any problems with the way your liver works, or if you have any problems with the way your kidneys work.

  • If you have a problem with your blood vessels, such as coronary artery disease or cerebrovascular disease.

  • if you have a heart condition or have recently had a heart attack.

  • If you are pregnant or breastfeeding.

  • If you have a rare inherited blood disorder called porphyria.

  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

  • If you have ever had an allergic reaction to any medicine.

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How to take hydralazine

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about hydralazine and will provide you with a full list of the side-effects which you could experience from taking the tablets.

  • Take hydralazine exactly as your doctor tells you to. It is usual to take one tablet twice a day. Try to take your doses at similar times of day each day, as this will help you to remember to take them regularly. There are two strengths of hydralazine tablet - it is usual to take the 25 mg strength tablet to begin with, but this may later be increased to the higher 50 mg strength tablet. Increasing your dose gradually allows your doctor to make sure that you have the dose that best helps your condition, but also keeps unwanted side-effects to a minimum.

  • Swallow the tablet whole with a drink of water. You can take hydralazine either with or without food.

  • If you forget to take a dose at your usual time, take it as soon as you remember unless your next dose is due. If your next dose is due then take the dose which is due but leave out the forgotten one. Do not take two doses together to make up for a missed dose.

Getting the most from your treatment

  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. You will need to have regular blood pressure measurements, and also some blood and urine tests from time to time.

  • Your doctor will advise you on what lifestyle changes you can make to help your condition. These could include losing weight if you are overweight, taking regular physical activity, eating a healthy diet, cutting back on the amount of alcohol you drink, stopping smoking, and reducing the amount of salt in your meals and caffeine in your drinks. It is important that you follow any advice you are given.

  • If you buy any medicines, check with a pharmacist that they are suitable for you to take. This is because some medicines (particularly some anti-inflammatory painkillers) can interfere with the way hydralazine works.

  • Treatment with hydralazine is usually long-term unless you experience an adverse effect. Continue to take the tablets unless you are advised otherwise by your doctor.

  • If you are having an operation or dental treatment, tell the person carrying out the treatment that you are taking hydralazine. This is because some anaesthetics can affect your blood pressure.

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Can hydralazine cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the more common ones associated with hydralazine. The best place to find a full list of the side-effects which can be associated with your medicine, is from the manufacturer's printed information leaflet supplied with the medicine. Alternatively, you can find an example of a manufacturer's information leaflet in the reference section below. Speak with your doctor or pharmacist if any of the following continue or become troublesome.

Very common

hydralazine side-effects

(these affect more than 1 in 10 people)

What can I do if I experience this?


Drink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the headaches continue, speak with your doctor

A fast heartbeat, the sensation of having a 'thumping heart' (palpitations)

If you are concerned, speak with your doctor


hydralazine side-effects

(these affect fewer than 1 in 10 people)

What can I do if I experience this?

Feeling flushed, swollen feet or ankles, chest pain

If any of these symptoms continue or cause you concern, speak with your doctor

Feeling dizzy

If this happens, sit down for a while until you feel better. Do not drive and do not use tools or machines while affected. Do not drink alcohol

Feeling sick (nausea) or being sick (vomiting), diarrhoea

Eat simple meals and drink plenty of water to replace lost fluids

Joint or muscle pain

Speak with your doctor about this as soon as possible. It may be an early sign of systemic lupus erythematosus-like syndrome

If you experience any other symptoms which you think may be due to the tablets, please speak with your doctor or pharmacist for further advice.

How to store hydralazine

  • Keep all medicines out of the sight and reach of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep-out-of date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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