The most common side effects are a long deep sleep and/or the best bowel movement ever! Some other possible side effects could be high energy and alertness, skin reaction, or less likely but possibly light flu-like symptoms for a day. This is more common if you have lots of toxins in your body. The oils help to remove these toxins, but if you have a bad virus that's stuck, and your body is ready, it can release them too quickly, thus causing flu-like symptoms. The most important thing to do is drink plenty of water before and after the treatment. Detox reactions are not bad (unless they are causing you a lot of pain and discomfort). Detox affect is actually a good sign that the oils are working.