There are systems in your body that work together to keep your blood pressure high enough to get sufficient oxygen and nutrients around your body. ACE inhibitors and ARBs lower your blood pressure by acting on one of these systems – the renin–angiotensin–aldosterone system.
Sensors in your kidneys can detect when your blood pressure drops too low. When this happens, a chemical called angiotensin I is released into your blood. This reacts with the angiotensin-converting enzyme in your blood, and is converted into angiotensin II. Enzymes are protein molecules that speed up chemical reactions.
Angiotensin II narrows your blood vessels. It also acts on your adrenal glands (that produce hormones) to trigger the release of a hormone called aldosterone. Aldosterone makes your body hold on to water. The extra volume of fluid in your blood and the narrowing of your blood vessels causes your blood pressure to rise.
Here’s how ACE inhibitors and ARBs work on this system.
- ACE inhibitors block the action of angiotensin-converting enzyme so that angiotensin I isn't converted to angiotensin II.
- ARBs block the action of angiotensin II.
Without the action of angiotensin II, your blood vessels become more relaxed and you don’t release the hormone aldosterone, so your blood pressure is reduced.
ACE inhibitors and ARBs can also protect your kidneys. If you have kidney disease, damage occurs to your kidneys and protein is lost in your urine. Lowering your blood pressure can prevent damage to your kidneys.
There are lots of different ACE inhibitors and ARBs. Your doctor will normally decide which is best for you after considering a number of factors. These include what condition you have, how effective the medicine is, and the cost. The most common ACE inhibitor is called ramipril, and the most common ARB is called candesartan. Ask your doctor which type of medicine is best for you.
You take ACE inhibitors or ARBs as tablets, usually once a day. When you have your first dose, it’s best to take it at night. If everything is well and you don’t get bad side-effects, you can take the tablets every morning.
You might need to take more than one medicine at the same time. For example, your doctor might prescribe a diuretic or a calcium-channel blocker in combination with an ACE inhibitor.
How often will I need check-ups?
Your doctor will ask you to have a blood test before you start taking ACE inhibitors or ARBs. They’ll test you again a week or two after you first start taking the medicine, or if they increase your dose. After this, your doctor will test you every year.
These tests are to check that your kidneys are healthy, and that your blood pressure is responding well to your medicine. After these tests, your doctor may change the type or dose of your ACE inhibitor or ARB. They might even change to a different medicine to make sure you’re getting the right treatment for you.
Will I have to take ACE inhibitors and ARBs for life?
Yes, you’ll usually need to take ACE inhibitors or ARBs on a long-term basis, with on-going monitoring. If you stop taking them, it’s likely you’ll stop getting the benefits. This is a big commitment and change to your lifestyle, so it’s important that you talk the pros and cons through with your doctor to make a decision you’re happy with.
It’s also important to improve your lifestyle with diet and exercise. This can improve your health condition so you might be able to take a lower dose of medicine. See our Related information for tips and advice on how to improve your diet and get more active.
ACE inhibitors and ARBs aren’t the right treatment for everyone.
If you're pregnant or breastfeeding, you won’t be able to take ACE inhibitors or ARBs because they may harm your baby. If you’re taking ACE inhibitors or ARBs and want to try for a baby, speak to your doctor first.
If you’re over 55 or are African or Caribbean, ACE inhibitors and ARBs might not work so well for you. Your doctor will probably give you a different medicine. See our FAQ: Suitability of ACE inhibitors for more information on why.
ACE inhibitors or ARBs may not be the right treatment if you have a narrowing of the arteries that supply your kidneys (renal artery stenosis). This is because these medicines may affect the way your kidneys work. Your doctor might ask you to have a blood test before you start taking them and further tests while you’re taking them. This is to check how well your kidneys are working and if you have this problem.
Check with your doctor or pharmacist before you take any other medicines at the same time as ACE inhibitors or ARBs.
Some medicines can enhance the effects of ACE inhibitors and ARBs so you might get very low blood pressure (hypotension). Other medicines that raise the potassium level in your blood can also cause problems if you take them together with ACE inhibitors or ARBs.
You can’t usually take both ACE inhibitors and ARBs together.
We haven’t included all the possible side-effects here. To understand all the side-effects of the medicine you’re taking, have a look at your patient information leaflet which will detail them all. ARBs usually cause milder side-effects than ACE inhibitors.
One in 10 people may get side-effects such as:
- low blood pressure
- a reduction in kidney function
- a persistent dry cough if you take ACE inhibitors (you don’t usually get this side-effect with ARBs)
One in 100 people may get side-effects such as:
- a skin rash
- cold-like symptoms
- feeling sick or vomiting
- diarrhoea or constipation
- tummy ache
- swelling underneath your skin
What to do if you get side-effects
If you get a cough or other side-effects with ACE inhibitors, let your doctor know. They may offer to prescribe you ARBs instead. If you get side-effects with ARBs, your doctor can discuss other options with you.
Alcohol temporarily relaxes your blood vessels and slows your heart rate (although over a longer period alcohol will increase your blood pressure). If you’re taking ACE inhibitors or ARBs, alcohol can temporarily enhance the effects and lower your blood pressure too much.
Low blood pressure is a common side-effect in people taking ACE inhibitors and ARBs and drinking alcohol makes this even more likely to happen. It can be dangerous if your blood pressure drops too much. It’s important to check with your doctor if you can drink alcohol when taking an ACE inhibitor or an ARB.
If you have diabetes, ACE inhibitors help to protect your kidneys from becoming damaged as a result of your condition.
With diabetes, you’re more at risk of getting kidney disease. This is because the high levels of glucose associated with diabetes can damage the small blood vessels in your kidneys.
High blood pressure can cause further damage to your kidneys. So if you have diabetes, it’s especially important to keep your blood pressure under control. If you have early signs of kidney disease or high blood pressure, your doctor will usually prescribe an ACE inhibitor. They seem to offer better protection against kidney disease than other medicines for high blood pressure.
Do angiotensin II receptor blockers (ARBs) increase your risk of cancer?
No, ARBs don't increase your risk of cancer.
In 2010, a study suggested that people taking ARBs had a slightly increased risk of cancer compared to those not taking the medicine. The researchers had looked at information from five clinical trials.
Since then, there have been three more reviews of all relevant clinical trials, including data from many more studies and thousands of patients. All three found no evidence to suggest ARBs increased the risk of cancer.
If you're taking ARBs and have any concerns, it's important to talk to your doctor or the healthcare professional who prescribed your medicine.
ACE inhibitors aren’t the best choice of treatment for everybody. They don’t reduce blood pressure in people over 55, and they don’t work as well in people with an African or Caribbean background.
ACE inhibitors seem to work better in younger people. This may be because people under 55 have a higher level of (and are more sensitive to) an enzyme called renin in their bodies. Renin is made by your kidneys and plays a key role in controlling your blood pressure. ACE inhibitors affect the renin–angiotensin system and it is thought this is why they have a better effect in younger people, while older people don’t respond so well.
ACE inhibitors are also not as effective at lowering blood pressure in people with from African or Caribbean ethnic groups. This is because they also tend to have lower levels of renin.
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Reviewed by Rachael Mayfield-Blake, Freelance Health Editor, December 2016
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