According to the sources, the failure rate for vasectomies is very low, with only one to two in 1,000 men experiencing a failed vasectomy. However, in rare cases, a vasectomy can fail if the doctor misses the vas deferens during the procedure, and the tube can regrow, though this is very uncommon. Another possible cause of failure is having sex too soon after the surgery, without using an alternate form of birth control.

I typically dont use pain killers before or after vasectomy. Just local anesthesia.