Several kinds of adverse medication reactions can occur. See the medication guidelines for tips on how to avoid common medication problems.

Side effects. Side effects are predictable but unpleasant reactions to a medication. They are usually mild but can be inconvenient. In some cases, they are more serious.

Allergies. Some people have severe, sometimes life-threatening reactions (called anaphylaxis) to certain medications. For signs of an allergic reaction, see the topic Allergic Reaction.

Medication interactions. These occur when two or more prescription or nonprescription medications or herbal supplements mix in a person's body and cause an adverse reaction. The symptoms can be severe and may be improperly diagnosed as a new illness.

Medication-food interactions. These occur when medications react with food. Some medications work best when taken with food, but others should be taken on an empty stomach. Some medication-food reactions can cause serious symptoms.

Overmedication. Sometimes the full adult dose of a medication is too much for small people and those over age 60. Taking too much of a medication can be very dangerous.

Addiction. Long-term use of some medications can lead to dependency, and severe reactions may occur if the medications are withdrawn suddenly. Narcotics, tranquilizers, and barbiturates must be taken very carefully to prevent addiction. For more information, see the topic Alcohol and Drug Problems.