After almost 20 years, I had to accept that my son was probably going to be addicted forever...and that his "forever" would most likely be brief because drugs kill. It was the most difficult acceptance I ever had to make.
My alternative was to keep believing that he would change, or worse, that I could make him change...and go down with him to the depths of darkness where addiction lives.
It's up to you to make your own choices, but like Tomsteve said, there is nothing "recreational" about using heroin. If you think it's just once in a while, it just means he's getting his using past you. Heroin doesn't DO once in a while.
Good luck, this must be hard for you.