From the article:
A recent review of nearly 7,000 studies of meditation practices found that less than 1% of them measured adverse effects. Willoughby Britton, an associate professor of psychiatry and human behavior at Brown University, said that this is largely because assessing adverse effects (a process known as “harms monitoring”) in non-pharmacological treatments like mindfulness-based meditation programs is difficult to do well.
To address that gap, Britton conducted a new study on adverse effects in mindfulness-based programs that identified common obstacles to harms monitoring and, importantly, showed how to address them. The study also found that the rates of adverse effects from mindfulness were similar to those found in other psychological treatments.