Statins should not be taken if you have severe liver disease or blood tests suggest your liver may not be working properly.

This is because statins can affect your liver, and this is more likely to cause serious problems if you already have a severely damaged liver.

Before you start taking statins, your doctor should carry out a blood test to ensure your liver is in a relatively good condition. You should also have a routine blood test to check the health of your liver three months after treatment begins, and undergo another after 12 months.

Pregnancy and breastfeeding

Statins should not be taken by women who are pregnant or breastfeeding, as there is no firm evidence on whether it is safe to do so.

If you do become pregnant while taking statins, contact your GP for advice.

People at an increased risk of side effects

Statins should be taken with caution if you are at an increased risk of developing a rare side effect called myopathy, which is where the tissues of your muscles become damaged and painful. This can lead to kidney damage (rhabdomyolysis).

Things that can increase this risk include:

• being over 70 years old
• having a history of liver disease
• regularly drinking large quantities of alcohol
• having a history of muscle-related side effects when taking a statin or fibrate (another type of medicine for high cholesterol)
• having a family history of myopathy or rhabdomyolysis

If one or more of these apply to you, there is a chance that frequent monitoring may be needed to check for complications. A lower dose of statin may also be recommended.

If you have an underactive thyroid (hypothyroidism), treatment may be delayed until this problem is treated. This is because having an underactive thyroid can lead to an increased cholesterol level, and treating hypothyroidism may cause your cholesterol level to decrease, without the need for statins. Statins are also more likely to cause muscle damage in people with an underactive thyroid.

Read more about the side effects of statins.

Interactions

Statins can react unpredictably with certain other substances (known as "interacting"), potentially increasing the risk of serious side effects, such as muscle damage.

Medications that can interact with some types of statin include:

• certain antibiotics and antifungals – including erythromycin, clarithromycin, daptomycin, itraconazole, ketoconazole and miconazole
• certain HIV medications – including indinavir, lopinavir, ritonavir and saquinavir mesilate
• warfarin – a medication commonly use to prevent blood clots
• ciclosporin – a medication that suppresses the immune system, which is used to treat a wide range of conditions including psoriasis and rheumatoid arthritis
• danazol – a synthetic hormone medication used to treat conditions such as endometriosis
• verapamil and diltiazem – types of medication called calcium channel blockers, which are used to treat various conditions affecting the heart and blood vessels
• amiodarone – a medication sometimes used to treat irregular heartbeats
• fibrates – medications that, like statins, help to reduce cholesterol levels in the blood

If you are taking statins and need to take one of these medications, your doctor may prescribe an alternative statin or prescribe your current statin at a lower dosage. In some cases, they may recommend that you temporarily stop taking your statin.

Food and alcohol

Grapefruit juice can affect some statins and increase your risk of side effects. Your doctor may advise you to avoid it or to only consume it in small quantities.

There are no known interactions between statins and alcohol.