Worth looking into this. The idea of the Pennebaker method goes back to a paper of his in 1986 that details the health benefits (including mental) of expressive writing. Sounds a lot like the underlying idea of morning pages, though that has the connotation of clearing one's head versus health related benefits.

Compare/contrast the two methods.

Is there research underpinning morning pages?

See also: Expressive Writing in Psychological Science https://journals.sagepub.com/doi/full/10.1177/1745691617707315<br /> appears to be a recap article of some history and meta studies since his original work.