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 be barely noticed and others can be more intrusive and make a noticeable difference to your 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.
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.