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.
Some side effects may be mild and manageable, such as headache, but some are more serious and potentially life threatening, such as allergic reactions.
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. Other side effects might be more intrusive and make a noticeable difference to your ability to go about your day normally.
The Patient Information Leaflet (PIL) supplied with your medication will list its known side effects and also tell you how common they are. One person is very unlikely to get all of the side effects listed. You can discuss the possible side effects of a drug with your doctor or MS team to help you decide whether you are comfortable taking it, balancing the potential benefit with the possible risks.
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.