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Side effects are unwanted effects caused by a medical treatment. They can happen with any drug, even something as everyday as aspirin can cause side effects in some people. Side effects are a possible, not an inevitable, occurrence from taking a drug and they are usually reversible. This means if you stop taking the drug, they will soon go away. 

Side effects can range from those that may be mild and manageable, such as headache, to those that are more serious and potentially life threatening, such as allergic reactions.

Some effects can pass by and be barely noticed and others can be more intrusive and make a noticeable difference to your wellbeing or ability to go about your day normally. Some side effects can be invisible to you, such as changes in blood cell counts, so you may be monitored by your health professionals, using tests or scans. If you are experiencing side effects that you are finding particularly difficult to deal with, do not stop taking your medication until you discuss this with your health professionals. There may be an alternative drug or dose that may be better for you.

Sometimes you might need to acknowledge that on balance you might need to accept the risk of developing or living with certain side effects, to receive the benefits of treatment. As the benefits are not always obvious or visible to you, it is important to discuss what to expect from your treatment with your health professionals.

The Patient Information Leaflet (PIL) supplied with your medication will list its known side effects and also tell you how common they are. If you experience a side effect that is not listed in the PIL, you can report it to the Medicines and Healthcare products Regulatory Agency (MHRA) using the YellowCard scheme.

Last updated: 10 September 2015
This page will be reviewed within three years