There are many kinds of bad reactions (adverse reactions) to medicine.

Side effects. A side effect is any effect other than the one you want. They tend to be mild, but they can still bother you. In some cases, side effects can be serious.

Allergies. Some people have strong reactions to some medicines. These reactions can be deadly. To learn the signs of an allergic reaction, see the topic Drug Allergies.

Medicine interactions. These happen when two or more medicines or herbal supplements mix in a person's body and cause a bad reaction. The symptoms can be severe and may be wrongly diagnosed as a new illness.

Medicine-food interactions. These happen when medicines react with food. Some drugs work best when you take them with food, but others should be taken on an empty stomach. Some medicine-food interactions can cause serious symptoms.

Overmedication. If you take too much of a medicine, it may trigger an adverse reaction. This can especially be a problem for people of small size and older adults. Sometimes the typical adult dose is too much for these people. Take your medicines exactly as prescribed. Call your doctor if you think you are having a problem with your medicine.

Addiction. Long-term use of some medicines can lead to dependency. You may have a severe reaction if you stop taking the medicine all at once. Find out from your doctor if a medicine may be addictive. To learn more, see the topic Alcohol and Drug Problems.

Decision Points are designed to guide you through key health decisions, combining medical information with your personal information to make a wise health decision. For help in learning the pros and cons of certain medicines, see a list of Decision Points About Medicines.