Medication side effects: when to worry
Nearly every medicine can cause side effects, but most are mild and fade as your body adjusts. Knowing which are which helps you avoid both needless worry and missed warning signs.
Often mild and temporary
- Mild nausea, headache, or drowsiness in the first days.
- Mild stomach upset (often eased by taking with food, if allowed).
- These often improve within a week or two.
Worth a call to your pharmacist or prescriber
- Side effects that don't fade or interfere with daily life.
- A new rash, ongoing dizziness, mood changes, or muscle pain.
- Anything that makes you want to stop the medicine — ask before stopping.
Emergency signs — don't wait
- Trouble breathing, swelling of the face/throat, or widespread hives (allergic reaction).
- Chest pain, fainting, or a severe, sudden headache.
- High fever with a spreading rash or blistering skin.
Don't quit cold turkey: Some medicines (like certain heart, seizure, or antidepressant medicines) need to be tapered. If side effects bother you, ask about adjusting rather than simply stopping.
Check your own medicines free
See how your prescriptions, supplements, and food may interact — organized by the part of the body they affect.
Open the medication tool →Important: This article is educational and not medical advice. It does not replace your pharmacist or prescriber. Always confirm decisions about your medicines with a qualified professional, and call your local emergency number for emergencies. In the U.S., Poison Control is 1-800-222-1222.