Coffee (caffeine related products really) from my understanding seems to harshly impact deep sleep.

If you are asking in good faith (which I hope you do because its HN and we are curious people, aren't we!), I recommend looking at r/decaf for seeing people's experience that they are sharing regarding it.

Also upvoting @bossyTeacher comments and re-sharing the good points that they have made:

- High heart rate and blood pressure

- Increased risk of arrhtymia

- Less deep sleep

- Disruption to your cortisol level dynamics

Interesting, as far as I remember, those effects did not show up in studies (yet?). But it's been years since I looked it up on examine.com which was mostly free back then.