Statins shouldn't be taken if you have severe liver disease or if blood tests suggest that 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 starting to take statins, you should have 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 3 months after treatment begins, and again after 12 months.
Statins shouldn't be taken by women who are pregnant or breastfeeding, as there's no firm evidence on whether it's safe to do so.
Contact your GP for advice if you become pregnant while taking statins.
Statins should be taken with caution if you're at an increased risk of developing a rare side effect called myopathy, which is where the tissues of your muscles become damaged and painful. Severe myopathy (rhabdomyolysis) can lead to kidney damage.
Things that can increase this risk include:
If one or more of these apply to you, you may need to be frequently monitored 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.
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:
If you're 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.
Grapefruit juice can affect some statins and increase your risk of side effects. Your doctor may advise you to avoid it completely or only consume small quantities.
Your doctor will also ask you how much alcohol you drink before prescribing statins. People who regularly drink large amounts of alcohol are at increased risk of getting more serious side effects.
If you're prescribed a statin, you may be able to continue drinking alcohol. However, you shouldn't drink more than 14 units of alcohol a week.
For full details of cautions and interactions relevant to your specific medication, check the patient information leaflet that comes with it.
If in doubt, contact your GP or pharmacist for advice.