Important note - the participants had already displayed relapses from medication based treatments, so they were already in a position where medication was not filling their needs.
I couldn't find the paper, either. But I did find a different paper, which is on much the same topic, and which has multiple authors in common with the paper mentioned in this post:
"Mindfulness-Based Cognitive Therapy to Prevent Relapse in Recurrent Depression", Journal of Consulting and Clinical Psychology, v. 76 (6) (2008), pp. 966-978.
https://www.plymouth.ac.uk/news/mindfulness-based-therapy-co...
I was unable to find the paper in Lancet's online system.