Side effects: how to spot them, lower risk, and what to do

Side effects are just the body's response to a medicine. Some are mild and pass in a few days; others can be serious and need quick action. Knowing what to expect and how to respond keeps you safer and less stressed when starting a new drug.

Quick checklist: common signs and drug-specific examples

Watch for these warning signs right away:

• Allergic reactions: rash, itching, swelling of face or throat, trouble breathing — get emergency care if this happens.
• GI issues: nausea, vomiting, diarrhea. Many antibiotics and pain meds do this; take with food if the leaflet says so.
• Unusual tiredness, yellowing skin or dark urine — could signal liver strain; seen with some statins or antibiotics.
• New or worsening muscle pain or weakness — common with some cholesterol drugs like simvastatin.
• Heart symptoms: fast or irregular heartbeat, fainting — certain drugs like Zithromax can rarely affect heart rhythm, especially in people with heart disease.
• Eye changes: blurred vision or eye pain. Steroid eye drops such as loteprednol can raise eye pressure in some people.
• Fever, sore throat or mouth ulcers after starting a medication — with drugs like methimazole this can be a sign of low white blood cells and needs urgent blood tests.

How to reduce risk and respond

Start by reading the leaflet and asking your pharmacist two quick questions: what are the top three side effects I might see, and what should make me call you or go to the ER? Keep a simple record for the first two weeks: dose, time taken, and any new symptoms. That helps your doctor spot patterns.

Simple steps that help: take meds with food when advised, avoid alcohol if the label warns, stay hydrated, and avoid mixing drugs without checking interactions. If a medicine can affect labs or the heart, ask for baseline tests — for example, blood tests for liver or potassium, an ECG if the drug can prolong the QT interval, or regular eye pressure checks for steroid eye drops.

Don’t stop some drugs suddenly. Stopping antidepressants like Zoloft without a plan can cause withdrawal. Call your prescriber to discuss dose changes or safe tapering. If a side effect is mild, your doctor might switch the time of day you take it or change to a similar drug with fewer problems — articles on our site cover alternatives for things like Lasix, Flagyl, and Fexofenadine.

If you get a severe reaction, seek emergency care. For non-urgent but worrying symptoms, contact your pharmacist or prescriber within 24 hours. Report serious adverse events to your local safety authority such as FDA MedWatch in the US — reports help improve safety for everyone.

Knowing common side effects and having a plan turns worry into action. If you’re unsure, bring your medication list to your next appointment and ask for specific things to watch for based on your health and other meds.