REVIEW OF: Li X et al, J Affect Disord 2026;405:121564
STUDY TYPE: Small, randomized sham-controlled trial
EVIDENCE GRADE: Moderate (7/10)
Background
Anhedonia is a the lack of interest, enjoyment, motivation and drive; an inability to experience pleasure that colors roughly 40% of depressions. It does not respond as reliably to antidepressants as other symptoms, and this trial tested light therapy for it.
Light therapy is already well established for depression, with dozens of controlled trials supporting a medium-to-large effect size (0.6-0.8, which is larger than for antidepressants) in both seasonal (winter) and non-seasonal depression. It is well-tolerated and works in conditions where antidepressants are unsafe or ineffective, such as in adolescents, pregnant women, and bipolar disorder. At least 7 practice guidelines endorse it, including the American Psychiatric Association.
The Trial
This single-blind, placebo-controlled trial randomized 81 hospitalized patients with moderate-to-severe depression to one of four arms: morning light therapy, morning placebo (dim light), evening light therapy, or evening placebo. Active treatment was 10,000 lx for 30 minutes daily over two weeks; placebo was 100 lx. All patients continued their standard medications. The primary outcome was the Revised Physical Anhedonia Scale (RPAS); secondary outcomes included HAMD scores and salivary melatonin and cortisol levels.
Morning light therapy produced a significant reduction in anhedonia scores compared to morning placebo, with meaningful time × group interaction effects. Evening light therapy did not — the evening groups showed no significant difference on anhedonia measures. Both morning and evening BLT improved HAMD depression scores compared to their respective placebo groups, suggesting the timing makes a difference for anhedonia but not general depression.
Morning light therapy also delayed melatonin onset (a sleep hormone released in evening) by about 1.5 hours, and that phase shift correlated with anhedonia improvement even after adjusting for age, sex, education, and illness duration. No significant cortisol effects were found (a stress hormone). The study had a high dropout rate (18 of 81), and a baseline gender imbalance between morning groups is worth noting.
Practice Implications
- Dose light therapy in the morning, most studies suggest between 5:00 am and 8:00 am — later for night owls and earlier for morning people. This study used 9:00 to 10:00 am as the morning.
- You can personalize the timing further with the AutoMEQ test, but don’t let perfection get in the way of pragmatics. Patients can still benefit from light therapy later in the day, but to prevent insomnia aim for delivery before 2:00-4:00 pm.
- Most commercial lightboxes do not treat depression. Stick to clinically tested products. Though bulkier and uglier, but deliver the right dose.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
Share Your Input in Comments
- What therapies have you found useful for anhedonia?
- What problems do your patients run into with light therapy?
