From the CMI:

Some of the more common side effects expected with Rectogesic are listed below.

Headache is a common side effect experienced with Rectogesic. These are usually mild and occur after the first few applications only, due to intolerance to the Rectogesic. The headache may be relieved with a simple analgesic, such as paracetamol.

After applying Rectogesic, you may also experience fainting effect or dizziness, particularly if you are an older person. Changing position slowly from lying or sitting to standing up may help you to avoid this problem. A possible effect is reduced control over your bowel movements and leaking of bowel motions although this is expected to be a rare event and has not been reported to date.

If you experience any of these unwanted effects, do not use any more ointment for at least eight hours, then continue treatment by reducing the amount of ointment by half. If the effect persists, stop the treatment and see your doctor. If anal bleeding increases, stop treatment and tell your doctor.

Overdosage may occur if you use too much ointment or if you are sensitive to the effects of Rectogesic. Some signs of overdosage are headache, fainting or dizziness. When these symptoms are experienced, you should stop using Rectogesic for at least 8 hours and then resume use with half the dosage. Simple analgesics such as paracetamol may provide temporary relief of headaches. If any of these symptoms persist, stop using Rectogesic and consult your doctor.

More information here.