Something else. I had four teenage kids and each one was a different proposition and different at different ages. I would have to read the situation. They usually know that drugs are harmful I don't think it's lecture time. It's listening time.
But I wouldn't react. My first response would be one of connection. Acceptance of them as a person and reaffirming the open door of communication because that's the golden pathway that doesn't always appear. I would want to know what was drawing them towards drugs. It could be the peer group. It could be anxiety, depression or dark thoughts. It could be misinformation. There's no prescription without a diagnosis.
Kids test you. They put out a piece of questionable information and if you overreact in their eyes they won't tell you the deeper issues.