Opioid painkillers are generally timed, meaning they are taken 0.5 to 1 hour before the estimated onset of pain. Opioid painkillers are generally used for analgesic treatment of cancer pain or long-term pain from some chronic conditions. For such people pain is usually chronic and requires analgesic medication. Opioid painkillers, like other oral medications, require a process of disintegration, absorption, and distribution after a period of time to work after being taken by mouth. That’s why opioid pain medications are generally taken empirically on a regular basis. Cancer pain and pain of chronic disease is usually a cyclical attack process, according to the interval time between two pain, before the next pain is about to attack 0.5 ~ 1 hour before taking, so that the drug after disintegration, absorption, distribution, to reach a certain concentration, to play the role of pain relief when the pain is just onset, so as to achieve the effect of pain relief. Opioid painkillers are strictly regulated by the state, and need to be used under the guidance of a professional doctor.