Vivitrol Shot

My son 23 is considering getting the vivitrol shot. He has been in and out rehabs and out patients for the past several years. He has been clean now for 2 weeks, but is getting urges again he tells me. We have discussed possibly getting the vivitrol shot. Do any of you have any experience with the shot or thoughts on it. I know it can be dangerous if he relapses and tries heroin again, but if he continues to use we end up with the same results. He does not attend NA meeting as he doesnt believe in god :( and says the meetings are not for him. He is currently talking to therapist weekly that recommended getting the shot. Any insight a comments will be appreciated.

Is he attending NA meetings regularly (daily) ??
he had been to NA meeting and says they are not for him. He is currently going to a therapist and we are looking in a group called smart recovery.
My daughter is on vivitrol. The shot may help the cravings, but I think the spiritual part of recovery is very important. He needs a higher power. It doesn't have to be God.