My daughter has done both over the years and as I haven’t seen her for a couple of months, I’m not sure which method she does now. Mainly she was smoking it, unless she hasn’t got enough money, she tends to inject.
Heroin addiction is an awful thing and I think the hardest part is accepting the fact that there is absolutely nothing you can do about it. It is completely out of your control and nothing will change until they want to change their lifestyle. Unfortunately, you have no control over that either and it makes you feel helpless. But remember, their addiction is not your fault.
Be strong and if you have accepted that there isn’t anything you can do, then you will find yourself in a better place. I think about my daughter every single day but still have to live my life as best as I can. I totally empathise with you and fully understand because I’m livig it too. Take care.