Radiotherapy may occasionally affect sexual function when it is given for cancers of the prostate , rectum and bladder . Adverse effects on erection are related to the dose used. The effects occur because of nerve damage or because blood vessels that supply the penis become scarred and are unable to let enough blood through to fill the penis. About one third of men treated in this way say that their erections are less strong than before. The changes are usually slow in onset, and can worsen over the first year or two following radiotherapy.
Some men get an erection but then lose it.
Others are unable to have one at all. Some feel a sharp pain as they ejaculate, caused by radiation irritating the urethra. This usually disappears within a few weeks after the treatment has ended. Chemotherapy Chemotherapy often reduces sexual desire. If people experience sickness, vomiting, weakness, depression, tiredness and lack of energy, this can affect the desire for sex.