Teen experimenting with herbal marijuana – does he need treatment?

I caught my son with some sort of herbal marijuana, and I’m not sure how worried I should be. He says it not real marijuana, only some sort of herb blend and that it’s not even really illegal or harmful. He says it’s no big deal and that he’s smart enough not to do ‘real’ drugs, and that I’m freaking out for nothing. My son has always been a really nice kid and a good student and involved in bands and sports other activities at school, but this year it seems different and we’re getting pretty concerned. He just turned 17 and he doesn’t seem to care about any of that stuff any more; he’s always hanging out with a new set of friends that I don’t really know and we’ve caught him coming home drunk a few times over the last year or so. We’ve tried grounding him and taking away his keys to the truck and talking about our worries but all we get in return is bad attitude and no change in his bad behaviors. My husband suggested we consider some kind of treatment program to deal with the drug taking before it gets too serious but when we brought this up with Andy he went crazy and said he wasn’t a drug addict and didn’t need any kind of help! Is my husband right? Should we get him into some sort of treatment program?