Overview
A side effect is an unwanted or unintended effect of a medicine. Side effects may affect the body or mood, and they can begin soon after starting a medicine or later during treatment. Not everyone gets side effects, and the same medicine may affect people differently.
Key Symptoms
Side effects can include nausea, upset stomach, diarrhea, constipation, dizziness, drowsiness, headache, dry mouth, or skin rash. Some medicines can also affect sleep, appetite, concentration, or sexual function. Serious reactions can include trouble breathing, swelling of the face or throat, severe rash, fainting, confusion, or unusual bleeding.
Causes and Risk Factors
Side effects can happen because of how a medicine works in the body, how it is broken down, or how it interacts with other medicines, alcohol, foods, or supplements. The risk may be higher when starting a new medicine, changing the dose, taking many medicines, or having kidney or liver problems. Past allergic reactions or sensitivities can also increase risk.
Who Is Affected
Anyone who takes a medicine can experience side effects. Older adults, children, pregnant or breastfeeding people, and people with long-term health conditions may need extra caution because medicines may affect them differently. People taking several medicines at the same time may have a higher chance of interactions and unwanted effects.
Prevention
Read the medicine label, leaflet, or pharmacy instructions each time, even if you have used the medicine before. Take medicines exactly as directed, and tell your healthcare professional about all prescription medicines, over-the-counter products, vitamins, and herbal supplements you use. Avoid sharing medicines, and ask before mixing medicines with alcohol or certain foods.
Diagnosis and Tests
A healthcare professional may review when the symptom started, what medicines you take, and whether the problem changed after a medicine was started, stopped, or changed. They may check for drug interactions, allergies, and other health conditions that can cause similar symptoms. In some cases, blood tests or other tests may be used to look for organ effects or to rule out other causes.
Treatment Categories
Treatment depends on the type and severity of the side effect. A healthcare professional may decide to monitor symptoms, change the medicine, change the timing, or use another treatment approach. Do not stop a prescribed medicine on your own unless you are told to do so, because suddenly stopping some medicines can be harmful.
When to Seek Medical Care
Seek medical advice if side effects are persistent, worsening, interfering with daily life, or making it hard to take the medicine as directed. Contact a healthcare professional promptly if you develop a new rash, severe vomiting or diarrhea, yellowing of the skin or eyes, unusual bruising or bleeding, mood changes, or signs of dehydration. It is also important to ask for help if you think two medicines may be interacting.
When It May Be an Emergency
Get urgent medical help right away for trouble breathing, swelling of the lips, tongue, or throat, chest pain, seizures, sudden severe confusion, fainting, or a severe blistering or peeling rash. Emergency care is also important after a suspected overdose or if a person cannot be awakened. If available in your area, contact emergency services or a poison center immediately.