A friend says they've finally been sleeping well, and they're sure cannabis is the reason. You know them. You believe they're telling you what happened.
You can believe their account without treating it as a treatment plan for yourself.
They may also have changed their routine, started another treatment, or moved past a stressful stretch. A personal story usually can't separate those possibilities. It also leaves out the people who tried something similar and felt no better, or felt worse.
Listen for the jump in the story
“I slept better” is an account of someone's experience. “This treats insomnia” is a much bigger claim.
The FTC's health-products guidance makes a related point: testimonials don't take the place of scientific support for health claims. A convincing story and good evidence aren't the same thing.
That doesn't mean you have to argue with your friend. You can ask what else changed and keep your own health decisions separate from the conversation.
If sleep is a problem for you, bring it up with a clinician. Explain how long it's been happening and what you've already tried. Don't stop prescribed treatment because someone else's story sounds promising.
A friend's experience can give you a question to ask. It can't supply your diagnosis or tell you what will work with your health history.