On 2 occasions, from different sources, I was told that a rumor is being spread about me that I am addicted to narcotics. It's untrue. I live in MA. My boss hasn't done anything about it. Do I have a right to meet with the person spreading the rumor? Do I have a right to sue for damages? How do I fix this terrible problem? Where do I get to say "Show me proof that your statement is true" when they can't prove it, do they get fired? Do I sue them? What happens next? A TON of people think I'm an addict. How can I get the word out that I'm not? Send Ms. Gossip around to groups telling them she's a Rumor Mill?
Your question has a lot of important factual issues balled up in it. Who and what constitutes this "group"? Why is your employer implicated -- is it a group at work? What kind of office or shop do you work in? Are you a union member? Are you in management? Is the speaker in management and senior to you? Has your career been affected by these statements?
It appears that it makes sense for you to find a lawyer with experience both in employment law and defamation law to listen to the full scope of your situation and advise you appropriately. Good luck.