Prescription medicines require a doctor or other healthcare provider to monitor both how well they work and possible side effects.

Aspirin and other salicylates can bring on severe asthma attacks in sensitive people. People with nasal polyps also may have breathing problems. Others at risk are those who have high blood pressure. Children and teens shouldn't be given aspirin because of its link to Reye syndrome, a potentially fatal illness.

Allergic reactions may include a rash, itching, and breathing problems.

Keep track of how many days in a row you take aspirin, ibuprofen, naproxen, or acetaminophen, the FDA says. If you're still having problems after seven to 10 days, see your healthcare provider. Seek medical care sooner if your symptoms get worse during those 7 to 10 days.

If you take more than an occasional dose of acetaminophen, don't drink alcohol. Overdoses of acetaminophen alone are toxic to the liver. Alcohol in combination with recommended dosages of acetaminophen may be toxic to the liver.

Antacids can increase or decrease the rate that other medicines are absorbed, or how well they are absorbed, or both. Another danger with taking antacids for long periods without a diagnosis is that they may mask a more serious problem, such as an ulcer, or esophageal or stomach cancer.

Antihistamines block histamine receptor sites, and older adults may have pronounced side effects, such as confusion, a dry mouth, lightheadedness, and problems with urination, the FDA says. A side effect of antihistamines is the blocking of a chemical neurotransmitter called acetylcholine. Older adults make less acetylcholine and can't use it as well.

Kitchen utensils aren't accurate for measuring medicine doses. Medicine or dosing spoons may look like wide straws with a spoon at one end. They are designed for children who can drink from a cup but are likely to spill. Measure the dose at eye level. Keep a written record of when you give the dose. This can prevent both missing a dose and accidentally overdosing a child.

Multi-symptom medicines expose you to medicines you don't need. This increases the risk for side effects. Ask the pharmacist for help in choosing the safest and most effective OTC medicine for your symptoms.