There is also research literature on heterosexual anal intercourse among drug-using subsamples, which has found a relationship between anal intercourse and both injection and non-injection drug use Bogart et al.
Pain as an insurmountable barrier to anal intercourse is consistent with the study by Stulhofer and Adkukovic.
Further questioning revealed that all of the participants had had anal intercourse, but some did not count it as such if the man did not ejaculate or if the woman insisted he withdraw because of pain.