Medication Side Effects (Adverse Drug Reactions)

Types of medication reactions

Common side effects by medicine group

• antibiotics: diarrhea, yeast infections, rashes. C. difficile colitis after some antibiotics
• NSAIDs (ibuprofen, naproxen): stomach upset, ulcers, bleeding, kidney strain, high blood pressure
• blood pressure medicines: dizziness, swollen ankles (amlodipine), cough (ACE inhibitors), frequent urination (diuretics)
• statins: muscle aches
• antidepressants: nausea, sleep changes, sexual side effects
• opioids: constipation, drowsiness, nausea, slowed breathing
• diabetes medicines: low blood sugar (insulin, sulfonylureas), stomach upset (metformin, GLP-1 agonists)
• steroids: raised blood sugar, mood changes, insomnia, weight gain, bone loss. See steroid-induced conditions
• antipsychotics: weight gain, drowsiness, movement problems such as tardive dyskinesia

Who is at higher risk

• older adults: changes in kidney and liver function and body composition mean drugs build up more. Sedatives, anticholinergic drugs and some sleep aids raise the risk of falls and confusion
• people taking many medicines (polypharmacy), including supplements and herbal products
• kidney or liver disease
• pregnancy and breastfeeding
• children, who need weight-based dosing
• genetic factors that change how drugs are processed or raise the risk of certain reactions

How to reduce your risk

• keep an up-to-date list of all medicines, supplements and herbal products and bring it to every appointment
• use one pharmacy where possible, so interactions are checked
• read the patient information leaflet and ask what side effects to expect and which are serious
• ask whether each medicine is still needed, especially if you take five or more
• tell all clinicians about past reactions and allergies
• avoid alcohol with sedating medicines
• use measuring devices for liquid medicines

What to do about side effects

1. Check the leaflet or ask your pharmacist whether the effect is known and expected.
2. Do not stop essential medicines such as blood thinners, seizure medicines, antidepressants, steroids or heart medicines suddenly without advice. Some cause dangerous withdrawal effects.
3. Ask about solutions: taking the dose with food or at a different time, lowering the dose, switching to another medicine, or treating the side effect.
4. Seek urgent care for warning signs listed above.
5. Report serious side effects to the FDA through MedWatch, online or by phone at 1-800-FDA-1088 (US). Your clinician can also report.

How doctors assess a suspected reaction

A clinician will consider timing (when the medicine was started), whether the reaction is known for that drug, whether symptoms improve when it is stopped (dechallenge), other possible causes, and blood tests where relevant, such as liver function, blood counts, kidney function and drug levels. Allergy testing or supervised challenges can clarify true drug allergies, such as penicillin allergy labels, many of which turn out to be incorrect.

Frequently asked questions

What are the most common side effects of medication?

The most common side effects are nausea, diarrhea or constipation, stomach upset, headache, dizziness, drowsiness, dry mouth and mild rashes. They are usually mild, often appear in the first days of treatment, and frequently fade as your body adjusts.

How do I know if I am having an allergic reaction to a medicine?

Allergic reactions include hives, itching, swelling of the face or lips, wheezing, difficulty breathing or faintness, usually within minutes to hours. Delayed reactions can cause widespread rash, fever, swollen glands or blistering days to weeks later. Severe symptoms need emergency care.

Should I stop taking a medicine if I have side effects?

Not without advice for most prescription medicines. Stopping some medicines suddenly can be dangerous. Call your pharmacist or prescriber to discuss options. Stop and seek emergency care only for serious reactions such as swelling, breathing trouble or a blistering rash.

How long do medication side effects last?

Many mild side effects ease within a few days to 2 weeks as the body adjusts. Some, such as dry mouth or sexual side effects, can persist while you take the medicine. Most go away after the medicine is stopped, though some reactions, like liver injury, take longer to resolve.

How do I report a side effect?

Tell your doctor or pharmacist, who can record it and report it. In the US, you can also report serious side effects directly to the FDA's MedWatch program online or by calling 1-800-FDA-1088. Reports help identify safety problems with medicines.