Unintended consequence vs. side effect? [closed]

In actual use, the intended meaning of these two phrases overlaps to the extent that you can't always tell the two apart.

However, "side effect" has a broader meaning. A "side effect" is just any effect that isn't the principal intended one.

For example, pharmaceuticals have "side effects" beyond the treatment of a patient's illness. Pharmaceutical companies are required to send a new drug through clinical trials before they are allowed to release it onto the market, and part of the reason for those trials is to determine what the side effects might be. They are also required to disclose the side effects, so that doctors and patients have a chance to know what they are and make an informed decision.

In programming, "side effect" has a specific meaning. See this Software Engineering SE question.

This includes any input and output from the program. These "side effects" are very much intended consequences!

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