The most common side effects of Botox are temporary and well tolerated. Injection site reactions may occur for up to the first week. These may include bruising, swelling, soreness and redness. In these cases, it’s often the injection itself, not the injected toxin, that causes the side effect.
Rarely, people may experience a mild headache or temporary neighboring muscle weakness (including a drooping brow or eyelid). In extreme cases of adverse reactions, symptoms of botulism may arise, such as difficulty breathing, speaking or swallowing, which is a medical emergency. Though these occurrences are uncommon, the risk of these reactions increases when untrained hands perform Botox in a non-medical setting.