Entonox is a mixture of oxygen and nitrous oxide gas. It won't remove all the pain but it can help to reduce it and make it more bearable. Many women like it because it's easy to use and they control it themselves. You breathe in the gas and air through a mask or mouthpiece, which you hold yourself. There are no harmful side effects for you or your baby but it can make you feel light-headed. Some women also find that it makes them feel sick, sleepy or unable to concentrate. If this happens, you can stop using it. Your midwife will help guide you on its use.