Definition: Side effects are the unplanned consequences of having taken a drug. Usually, a side effect is unwanted, such as an allergic reaction. Side effects can occur outside of or away from the area for which the drug is intended. Quite often, but not always, side effects are not serious, and go away on their own.
Examples:Potential side effects of taking aspirin or other NSAID long term for spinal arthritis are stomach ulcers or bleeding of the somach lining.