I would talk about specific truths and facts. I would also say..... “Just say no”, isn’t completely stupid. It’s completely stupid as a general propositiom, but you know what? Pointing out that certain drugs are way more likely to cause pointless harm (say for example, tobacco, or cocaine, opiates, etc.) isn’t a terrible idea I don’t think. I would actually talk about “just say no” to them, and explain it as a tactic that has generally been agreed to have been a failure - but then explain why it was in any way a desirable tactic in the first place.

I’d point out the difference between drugs that are basically a bullet train to heck (like opiates), and other drugs that responsible adults use, and describe the risks they come with - and how extreme those risks can become. Talk about how alcohol can* become as extreme a problem as opiates become (while being careful to explain how opiates almost universally develop into that level of extremity when used recreationally on anything approaching a regular basis). Explain how in some states marijuana is being legalized and how in Canada it is legal because it does not have the extreme problems associated with alcohol - and then explain the problems that can indeed come with marijuana.

Basically, tell them where “just say no” actually is a rational proposition, and where in other cases they may want to tread carefully, and how carefully they may want to tread in those areas. Describe a realistic hierarchy of risk and fill in the details of why and how they earn their places in that hierarchy. “Just say no” to cannabis or even alcohol, is dumb. These are drugs that have risks, but are acceptable in terms of risk for experimentation for responsible adults. Just say no to dilaudid? Not a bad idea. That one’s gonna come with so much risk it’s just better to not bother there, ever.