Thank you for your question about juvederm side effects. First and foremost, fillers in the brow/forehead area must be done by a very experienced injector. There are risks associated with injecting fillers in any area, but the forehead has a large risk of vascular compromise. As with any HA filler injections, you can expect some short term side effects after Juvederm injections. The most common are bruising at the site of the injection and mild swelling over the areas treated. Hyaluronic Acid Fillers, including Restylane Defyne are "hydrophilic" and attract and hold on to water, causing swelling. This is typically mild and only lasts for a few days. Your provider should also counsel you on post injection care. This includes, but is not limited to, avoiding exercise for 24 hours, avoidance of aspirin/ibuprofen/fish oils to avoid bruising, avoiding heat or sun exposure for 24 hours, avoid waxing or laser treatments to the area for 24 hours, and avoiding massage of the injection site. To be sure, see two or more experienced, licensed and board-certified providers in your area for a complete evaluation to make sure you are a good candidate and that it is safe for you to have treatment. I hope this helps.