Opioids can be administered via a number of systemic routes. The choice of route will depend on multiple factors including site and severity of the pain; patient factors such as age, cognitive ability, and willingness to accept a technique; and organizational factors including cost, staff education, and the level of monitoring and supervision available. In the absence of any contraindications, the oral route is the route of choice for opioid administration, unless a patient has severe acute pain. It is simple, effective, and well tolerated by most patients. Immediate-release oral opioid preparations such as those of oxycodone, morphine, and hydromorphone are preferred for the initial and early management of acute pain. In most cases their peak effect will be obtained within about 45–60 minutes. The submucosal venous plexus of the rectum drains into the superior, middle, and inferior rectal veins.