Do opiates cause loss of appitie?

Opiods. Opioids most certainly can lead to loss of appetite. Much depends on your personal pharmacodynamic response but in general opioids can less to decreased gastric/intestinal motility and constipation which could certainly lead to decreased appetite. This is in addition to the other reasons you would see in an opioid addiction setting.
Yes. Many people get a loss of appetite, nausea and vomiting and constipation.