My Boyfriend Is Now Into Day 20 Of Receiving The

My boyfriend is now into day 20 of receiving the Vivitrol injection. He has used heroin twice (IV) and states he did feel high... not as pleasureable as past uses but still received a pleasure effect. This is his first injection of Vivitrol - does it take more than one treatment in order for the receptors to start blocking the pleasure sense from opiates?