What does science say about the effects of meditation?

https://www.medicalnewstoday.com/articles/324839.php

negative effects of meditation, side-effects

The investigators note that most of the unwanted effects — 41.3 percent — occurred during individual, not group, practice. They also report that 17.2 percent of the unwanted effects took place in the course of focused attention meditation and that 20.6 percent occurred when a person meditated for longer than 20 minutes.

According to the researchers, 39 percent of these unwanted effects did not last long and were not severe enough to require medical intervention.

The authors of a review analyzing the findings of other studies that reported potential adverse effects of mindfulness practices argue that "rather than mindfulness per se, [...] it is a lack of understanding of the nuances of mindfulness among some instructors — and the subsequent poor teaching of mindfulness — that is likely to pose the greatest risk to patients."