Side effects: how to spot and manage medication reactions

Almost every medicine can cause side effects. Some are mild and short-lived — like nausea or drowsiness — while others need quick medical attention. Knowing what to expect and what to do can keep you safe and let treatments work better.

What to watch for

Start by reading the leaflet that comes with your prescription. Look for common effects (nausea, headache, constipation, sleep changes) and serious warnings (allergic reactions, severe rash, difficulty breathing, chest pain, yellowing of skin or eyes). Timing matters: some reactions happen within hours, others appear after weeks or months.

Pay attention to new symptoms that show up after starting a drug or after changing the dose. Also watch for changes when you add a new medication, supplement, or even grapefruit juice — many items alter how drugs break down in the body.

When to call your doctor or get help

Call right away if you have trouble breathing, swelling of face or throat, fainting, severe chest pain, sudden weakness or confusion, or a fast heartbeat. These could be signs of a serious allergic or cardiovascular event. For high fevers, severe diarrhea, or a widespread blistering rash, seek urgent care. If you aren’t sure, call your pharmacist or doctor — they can often advise whether the symptom is expected or dangerous.

Not all worrying signs are emergencies. Mild nausea, temporary dizziness, or a change in taste can often be managed at home or discussed during your next visit. Still, don’t ignore persistent or worsening symptoms.

Some drugs need lab checks: liver enzymes, kidney tests, blood counts, blood sugar, or cholesterol. If your medication requires monitoring, follow the schedule your provider gives you. Skipping labs can let a serious side effect go unnoticed.

Older adults and pregnant people are more likely to have problems from medicines. Doses often need adjusting for age, weight, kidney or liver function, and pregnancy. Make sure your prescriber knows your full medical history and all other drugs you take — including vitamins and herbal products.

Practical steps to lower risk: keep a single, updated medication list; use one pharmacy so they can spot interactions; take drugs exactly as directed; avoid alcohol unless you check first; report side effects early; and ask about starting at a lower dose if you’re worried about reactions.

Finally, trust your instincts. If something feels off after a new drug, ask. A quick call to a pharmacist or clinic can prevent bigger problems and help you stay on the right treatment safely.