Identifying distinct trajectories of change in anhedonia during psychological treatment for depression

While initial anhedonia predicts poor psychotherapy outcomes, little is known about its trajectory during treatment. This study aimed to: (1) identify distinct anhedonia trajectories during high-intensity depression treatment; (2) examine patient and treatment predictors; and (3) compare outcomes across treatment types.

Sessional anhedonia scores (PHQ-9 item-1) from 22,605 patients in NHS talking therapies (primarily receiving either cognitive-behavioral therapy [CBT] or counseling for depression [CfD]) were analyzed using latent growth curve (LGC) and growth mixture modeling. Multinomial logistic regression examined predictors of class membership.

A quadratic LGC model best fit the data, reflecting a decrease in symptoms before leveling out. Six latent classes emerged. Notably, three "non-responder" classes characterized by linear-stable or minimal-change patterns comprised over 50% of the sample (51.3%). In contrast, two "responder" classes (41.4%) exhibited improvement, typically shifting between sessions 4 and 6. This suggests an early "inflection point" where the trajectory of recovery is established. Poorer response was predicted by unemployment, chronic health conditions, psychotropic medication, and longer wait times. There was only a sufficient sample size to compare CBT and CfD treatment types. While CBT was associated with membership in specific classes, the probability of being a "responder" did not differ significantly between CBT and CfD.

Most patients followed non-responder trajectories, highlighting a major efficacy gap for anhedonia in standard depression protocols. The 4-6 session window suggests that if improvement is not observed early, the treatment strategy may require further evaluation. Further research into targeted anhedonia interventions is essential.