Candesartan side effects: what you should know

Candesartan is generally considered one of the best-tolerated blood pressure medicines available.

In clinical trials, the overall incidence of side effects was only slightly higher than placebo.

Common side effects (affecting up to 1 in 10 people):

• Dizziness: the most frequently reported side effect, typically occurring when you first start the medicine or after a dose increase
• Headache: usually mild and resolves within the first week
• Upper respiratory tract infection: cold-like symptoms such as a sore throat or runny nose have been reported in trials, though the link to candesartan is uncertain

Uncommon side effects (affecting up to 1 in 100 people):

• Hyperkalaemia (high potassium), detected on blood tests
• Low blood pressure (hypotension), especially after the first dose
• Back pain or joint pain
• Nausea
• Fatigue

The BNF notes that candesartan is particularly well suited for patients who have experienced side effects with other blood pressure medicines.

Its clean side-effect profile is one of the reasons it is widely prescribed across the NHS, both for hypertension and heart failure.

Like all ARBs, candesartan can raise potassium levels in the blood by reducing aldosterone secretion.

This is the same mechanism seen with losartan and other medicines in this class.

Risk factors for hyperkalaemia:

• Chronic kidney disease (the kidneys are less able to excrete potassium)
• Diabetes (insulin resistance affects potassium handling)
• Concurrent use of potassium-sparing diuretics (spironolactone, eplerenone, amiloride)
• Use of potassium supplements or potassium-containing salt substitutes
• Elderly patients with declining kidney function
• Combination with an ACE inhibitor (dual RAAS blockade, which is generally avoided)

Monitoring recommendations (NICE and BNF):

• Check renal function and potassium before starting candesartan
• Recheck at 1 to 2 weeks after starting or changing the dose
• At least annual monitoring during long-term treatment
• More frequent checks in high-risk patients

Signs of high potassium to watch for:

• Muscle weakness or heaviness in the legs
• Tingling or numbness
• Irregular or slow heartbeat
• Nausea

If you experience any of these symptoms, contact your GP promptly. Severe hyperkalaemia is a medical emergency.

Serious side effects of candesartan are rare but important to recognise.

Angioedema:

Swelling of the face, lips, tongue or throat can occur, though this is much rarer with ARBs than with ACE inhibitors. If you develop sudden swelling or difficulty breathing, call 999 immediately.

Patients with a history of ACE-inhibitor-related angioedema should be monitored closely when switching to an ARB.

Acute kidney injury:

Candesartan can reduce kidney function, particularly in patients who are dehydrated, have heart failure, bilateral renal artery stenosis or are taking NSAIDs.

Your doctor monitors kidney function with blood tests to detect any decline early.

Severe hypotension:

A marked drop in blood pressure is most likely after the first dose in patients who are volume-depleted (for example, after heavy diuretic use, vomiting or diarrhoea).

Symptoms include dizziness, blurred vision and fainting.

Hepatic effects:

Very rarely, candesartan has been associated with liver function abnormalities. Report any unexplained nausea, abdominal pain, dark urine or yellowing of the skin to your doctor.

Pregnancy:

Candesartan must not be used during pregnancy. All ARBs can cause serious harm to the developing baby, particularly in the second and third trimesters.

If you become pregnant while taking candesartan, stop the medicine and contact your doctor immediately.

Candesartan belongs to the same class as losartan, valsartan and irbesartan, but there are some differences worth noting.

Candesartan advantages:

• Potency: candesartan has a higher binding affinity for the AT1 receptor than losartan, which may translate to more consistent blood pressure control
• Longer duration of action: candesartan provides effective 24-hour blood pressure control, which is important for patients who occasionally miss or delay a dose
• Heart failure evidence: the CHARM programme demonstrated clear benefits for candesartan in heart failure with both reduced and preserved ejection fraction. NICE (NG106) lists candesartan as a recommended ARB for heart failure
• Migraine prevention: candesartan has good evidence for migraine prophylaxis (off-label use), with trials showing it is as effective as propranolol

How it compares to losartan:

• Both are available as affordable generics on the NHS
• Losartan has specific evidence for diabetic nephropathy and stroke prevention
• Candesartan has specific evidence for heart failure across the ejection fraction spectrum
• Side-effect profiles are very similar

Your doctor will choose the most appropriate ARB based on your specific condition and any additional indications.

The good news is that most candesartan side effects are mild and manageable.

For dizziness:

• Stand up slowly from sitting or lying positions, particularly in the first few days of treatment
• Avoid driving or using machinery until you know how candesartan affects you
• Stay well hydrated
• Avoid excessive alcohol

For headache:

• Paracetamol is safe to take alongside candesartan
• Headaches usually resolve within the first week of treatment
• If persistent, speak to your GP

For high potassium:

• Attend all scheduled blood test appointments
• Avoid potassium supplements and low-sodium salt substitutes
• Be mindful of high-potassium foods if your levels are borderline
• Inform your doctor about all other medicines you are taking

For low blood pressure:

• Ensure adequate fluid intake, particularly in hot weather
• If you are also taking a diuretic, your GP may temporarily reduce the diuretic dose before starting candesartan

General advice:

• Take candesartan at the same time each day
• Do not stop without medical advice
• Keep all follow-up appointments for blood pressure and blood test monitoring
• See our candesartan NHS information page for prescribing and availability details

Most candesartan side effects do not require urgent treatment, but there are situations where you should act quickly.

Contact your GP or call 111 if you notice:

• Persistent dizziness that is not improving after the first week
• Swelling of the ankles, feet or legs
• A marked reduction in the amount of urine you pass
• Muscle weakness, tingling or an irregular heartbeat (possible high potassium)
• Unexplained nausea, dark urine or yellowing of the skin or eyes

Call 999 or go to A&E if you experience:

• Swelling of the face, lips, tongue or throat (angioedema)
• Difficulty breathing or swallowing
• Fainting or collapse
• Severe chest pain or a very fast or irregular heartbeat

The NHS recommends that you continue taking candesartan as prescribed, even when you feel well.

High blood pressure usually has no symptoms, and stopping treatment without medical advice can put you at risk of stroke, heart attack or kidney disease.