I had a failed attempt at an endometrial biopsy with no drugs at all. They were unable to push the little plastic stick through the cervix. It wasn't that painful, but then again, they didn't get a sample of the endometrium. From reading this forum, failed endometrial biopsies seem to be pretty common. Some doctors prescribe vaginal misoprostol pills beforehand, which apparently increase the success rate. Might be worth asking about.