Others claim losing an average of pounds a month with Phent pills, although some of that weight loss is due to water weight. After the first week or so, some seemed to stall in their weight loss efforts between pounds a month. An average expected weight loss can range anywhere between pounds a month..User Reviews for Phentermine to treat Weight Loss. Also known as Adipex P, Lomaira, Atti Plex P, Pro Fast HS, Pro Fast SR, Pro Fast SA. The following information is NOT intended to endorse drugs or recommend therapy..