Phenoxybenzamine - an alpha-blocker

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Adults will normally start with one capsule a day. This dose may then be increased over the next few days.

It is common to feel dizzy or light-headed initially. This should soon settle.

You may be given other medicines to take alongside phenoxybenzamine.

Type of medicineAn alpha-adrenoceptor blocker (also called an alpha-blocker)
Used forHigh blood pressure caused by phaeochromocytoma
Available asCapsules

Phaeochromocytoma is a tumour of your adrenal glands. With phaeochromocytoma, large quantities of chemicals are released from your adrenal glands, which narrow (constrict) your blood vessels. This causes episodes where your blood pressure increases significantly.

The treatment of choice for phaeochromocytoma is removal of the tumour by surgery. Phenoxybenzamine is sometimes prescribed as a short-term option in preparation for the surgery. It works by blocking sites on your blood vessels, known as alpha-receptors. This blocking action reduces your high blood pressure.

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 phenoxybenzamine it is important that your doctor knows:

  • If you are pregnant or breast-feeding.
  • If you have problems with the way your kidneys work.
  • If you have heart disease, or if you have recently had a heart attack.
  • If you have ever had a stroke.
  • If you have a rare inherited blood disorder called porphyria.
  • If you have ever had an allergic reaction to a medicine.
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about phenoxybenzamine, and will also provide you with a full list of side-effects which you could experience from taking it.
  • When you start the treatment, your doctor will give you a small dose (one capsule a day) and will then gradually increase your dose over the next few days as necessary. Take phenoxybenzamine capsules exactly as your doctor tells you to. The directions will be printed on the label of the pack of capsules to remind you about what the doctor said to you.
  • Try to take your doses at the same time of day each day, as this will help you to remember to take them regularly. You can take phenoxybenzamine either before or after a meal. Swallow the capsule with a drink of water.
  • If you forget to take a dose at your usual time, take it as soon as you remember. If you do not remember until the following day, leave out the forgotten dose from the previous day and take the dose that is due as normal. Do not take two doses at the same time to make up for a missed dose.
  • Keep your regular appointments with your doctor. This is so your doctor can check on your progress.
  • If you buy any medicines, check with a pharmacist that they are suitable for you to take alongside phenoxybenzamine.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains the most common ones associated with phenoxybenzamine. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any continue or become troublesome.

Phenoxybenzamine side-effects
What can I do if I experience this?
Feeling dizzy or faint, especially when you get up from a lying or sitting positionGetting up more slowly may help. If you begin to feel dizzy, lie down so that you do not faint, then sit for a few moments before standing. Do not drive, or use tools or machines while affected
Feeling tired, blocked nose, eyesight problems, ejaculatory problems, a fast heartbeat, stomach upset, diarrhoeaIf any of these become troublesome, speak with your doctor

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

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

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 at once. 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.

If you are due to have an operation or dental treatment, please tell the person carrying out the treatment which medicines you are taking.

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.

Further reading & references

  • Manufacturer's PIL, Phenoxybenzamine 10 mg Capsules; Amdipharm Mercury Company Limited, The electronic Medicines Compendium. Dated December 2013.
  • British National Formulary; 70th Edition (Sep 2015) British Medical Association and Royal Pharmaceutical Society of Great Britain, London

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr John Cox
Document ID:
1459 (v24)
Last Checked:
Next Review:
The Information Standard - certified member

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