As a side effect is a commonly used phrase that denotes an inadvertent consequence of a certain action or situation. However, if you are tired of using the same old phrase repeatedly, you can try out the following synonyms that convey the same meaning - byproduct, secondary effect, unintended consequence, collateral damage, spin-off effect, corollary, repercussion, aftermath, result, and outcome. Using these synonyms in your writing can enhance the flow of your content and make it more interesting and attention-grabbing. So, next time when you want to convey the unintended consequence of something, use the above synonyms to express your thoughts with a fresh perspective.