My adult daughter is addicted. What can I do?

I have a very strong suspicion that she and her boyfriend are addicted to heroin. Should I continue to act as if I don't know it? She would be furious if I mentioned it. My husband thinks we shouldn't say anything about it in the hopes of some day being able to denounce the boyfriend for drug dealing without them knowing we were the ones who snitched. But I don't know. Maybe if I started mentioning the drugs to her in casual conversation, she would eventually be more open about it and more receptive to getting help and going to rehab. Such a wretched thing it is having a daughter who is on drugs - the fear, the isolation. It destroys everything. How can I help her get out of this trap?