Narcotics are also divided into categories, called Schedules, by the government. Hydrocodone compounds, such as Vicodin, are Schedule III; many other narcotics are in Schedule II. For the patient, a major difference is that a physician can call or fax in a Schedule III prescription to the pharmacy, whereas a Schedule II medication requires a tamperproof prescription which the patient must deliver directly to the pharmacy.

Narcotics can be classified as either immediate release, with an effect lasting several hours, or sustained release, with effects lasting anywhere from eight hours to three days. Physicians use the sustained release forms primarily for chronic pain, where there is a continual need for pain relief. The intent is that by providing constant relief, the person suffering from chronic pain can focus on living their life (maintaining function) rather than constantly worrying about taking the next pill. In this way, physicians hope to minimize the occurrence of addiction.

Immediate release medications are used in the chronic pain setting to treat breakthrough pain, or short-lived (up to about an hour) pain which occurs because of increased activity or sometimes for no reason at all. Breakthrough episodes, if they do occur, can occur up to three to four times per day. There are many commonly prescribed immediate release medications, including preparations of morphine, oxycodone, hydromorphone, oxycodone, meperidine, oxymorphone and fentanyl. Most of these medications are pills. Fentanyl comes in two preparations, Actiq and Fentora, which allow it to be absorbed into the blood stream through the lining of the mouth. Actiq and Fentora have the advantage of vary fast onset and have been approved by the FDA for cancer breakthrough pain.