Side effects: what to watch for and what to do

Side effects are the reason many people stop a medicine or worry about taking one in the first place. Some are mild and pass in a few days. Others need quick action. This page collects practical tips so you can spot trouble early and handle side effects without panic.

Common vs serious side effects — quick examples

Common side effects you’ll often see: nausea, headache, dizziness, mild stomach upset, and sleep changes. For instance, metformin (Glucophage) often causes temporary gut upset, and benzodiazepines like diazepam commonly cause drowsiness.

Serious warning signs need immediate attention: rash with blisters, swelling of face or throat, trouble breathing, high fever, yellowing of skin or eyes, fainting, sudden severe muscle pain, or chest pain. Statins (like simvastatin or rosuvastatin) can cause muscle pain that rarely leads to severe muscle breakdown. Antibiotics like Bactrim can trigger serious allergic reactions or blood changes in some people. If you notice any of these, seek emergency care.

Practical steps if you notice a side effect

Stop taking the drug only if the reaction is severe or your doctor told you to stop. For mild side effects, call your pharmacist or prescriber first — they can tell you if the symptom is common or needs testing. Keep a simple note: what happened, when it started, and any other meds or supplements you were taking. That timing often reveals whether the medicine caused the problem.

If you have breathing trouble, swelling, fainting, or severe chest pain, call emergency services right away. For less urgent but worrying symptoms (new rash, persistent vomiting, signs of infection), contact your prescriber within 24 hours.

Avoid making changes based on guesswork. Don’t mix alcohol with sedatives or opioids. Don’t stop antidepressants or benzodiazepines abruptly — withdrawal can be dangerous. If a side effect looks dose-related, your clinician may lower the dose or suggest a safer alternative.

Want to reduce your risk? Always tell your provider about all prescriptions, over-the-counter drugs, and supplements. A herbal pill or a thyroid supplement can change how a drug works. Watch out for common interactions — grapefruit affects some statins and other meds; combining potassium-sparing drugs and certain diuretics can raise potassium dangerously.

Keep routine checks: blood tests for kidney and liver function, cholesterol monitoring if you’re on statins, and periodic review for long-term drugs like proton-pump inhibitors. Use a medication list or an app so every clinician sees the full picture.

Finally, report problems. In the U.S., use FDA MedWatch; in the U.K., use the Yellow Card scheme. Reporting helps regulators spot rare risks sooner and protects others. Browse our drug-specific articles below to get detailed side-effect info for medicines like simvastatin, metformin, diazepam, Bactrim, and more.