Complex sentence: He has also published research on the nocebo effect, in which he found that cholecystokinin is responsible for the transmission of pain by the nocebo effect, and that drugs used to block this chemical can also stop nocebo pain.
Split into simpler sentences: He has also published research on the nocebo effect, in which he found that cholecystokinin is responsible for the transmission of pain by the nocebo effect. This research also found that drugs used to block this chemical can also stop nocebo pain.