Depression Is the Strongest CBT-I Outcome Predictor — and Knowing That Can Change What You Do Next

Depression — not anxiety — is the strongest predictor of long-term CBT-i outcomes. Here’s what a four-year study of over 1,000 insomnia patients means for your treatment plan.

You finished a course of CBT-i. For a few months, things were better — you fell asleep faster, woke less often, and the days felt more manageable. Then, slowly, the old patterns crept back: the racing mind at 2 a.m., the heaviness in the morning, the doubt about whether the therapy even worked.

If that sounds familiar, you are not alone — and it is not your fault. A significant number of people who complete Cognitive Behavioural Therapy for Insomnia experience some relapse, especially after the first year. A major study published in Frontiers in Neuroscience followed over a thousand insomnia patients for up to four years and found a clear answer to who is most likely to slide back — and it is not who most people expect. The single strongest predictor of long-term CBT-i outcomes was not anxiety. It was baseline depression.

TL;DR: A four-year study of 1,022 insomnia patients found real CBT-i gains in the first year — but a mild relapse pattern after month 12. The strongest predictor of who struggled long-term was baseline depression severity (PHQ-9), not anxiety and not insomnia severity. When depression is addressed alongside insomnia, outcomes for both improve substantially. The two most clinically important takeaways: routine depression screening before CBT-i, and planned follow-up after it.

What the new research found

Huang and colleagues (2026) tracked 1,022 insomnia patients for up to 48 months. Participants received mobile-delivered CBT-i alongside standard pharmacotherapy, with sleep quality (PSQI), depression (PHQ-9), anxiety (GAD-7), daytime sleepiness, and somatic symptoms measured from two weeks out to four years.

The results were encouraging and sobering at once. In the first 12 months, patients improved significantly across every domain — median PSQI dropped from 15 to around 9–10 by month three, and depression scores fell by roughly half. But after the 12-month mark, a mild relapse pattern emerged: small but statistically significant upward trends across sleep, mood, and somatic symptoms. Not a return to square one — but enough to matter clinically.

The headline finding: baseline PHQ-9 score was the single strongest predictor of outcomes across every symptom domain — sleep quality (β = 0.091, p = 0.008), daytime sleepiness (β = 0.154, p < 0.001), and somatic symptoms (β = 0.122, p < 0.001). Depression at the front door predicted what happened years down the road. The study’s conclusion was direct: routine depression screening before CBT-i is essential for risk stratification and follow-up planning.

Why does depression undermine CBT-i — even when anxiety feels like the problem?

Most people who come to us for insomnia treatment identify anxiety as the culprit, and lying awake with a racing mind certainly feels like anxiety. But once depression was accounted for, baseline anxiety showed limited independent prognostic value. Anxiety on its own did not reliably predict who would struggle over time. Depression did.

This does not mean anxiety is irrelevant. It means that what looks like anxiety-driven insomnia may actually be insomnia shaped by an underlying depressive process — one that drains energy, flattens motivation, and narrows the cognitive bandwidth CBT-i requires. CBT-i is not passive: it asks you to keep a sleep diary, restrict your time in bed, get out of bed when you cannot sleep, and challenge your thought patterns about rest. Adherence research shows only about half of patients closely follow prescribed sleep restriction schedules in the first four weeks (Muench et al., 2022). Layer depression on top, and the executive function and motivation needed to stick with the plan are already compromised.

That is why “CBT for insomnia not working” is rarely about willpower. It is more often about an unaddressed condition making the treatment harder to complete as designed.

What happens after month 12? The 12-month drift

Gains from CBT-i are real and substantial in the first year. After month 12, there is a gentle drift back toward symptom return — what we might call the 12-month drift. This is not failure; it is a known, manageable pattern.

Think of physiotherapy for a knee injury: the initial course gets you functional, but if you stop all exercises and never check in, the knee stiffens. Sleep works the same way. That is where booster sessions come in — typically one to three sessions spaced months apart, about 50 minutes each, covering three things: what has changed in your sleep since the last check-in, which CBT-i strategies have slipped, and whether your mood warrants closer monitoring. For insomnia complicated by depression, boosters may include a brief PHQ-9 re-screen — because a dip in mood and a dip in sleep quality tend to travel together.

Without proactive follow-up, the mild relapse often goes unaddressed until a full-blown insomnia episode returns. The answer is usually not that CBT-i failed. The answer is that no one checked in.

What this means if you’re starting CBT-i in Saskatchewan

If you have depression alongside insomnia, this research does not mean CBT-i won’t help you. The evidence points the opposite way: treating insomnia can significantly improve depression.

Key finding: Adding CBT-i to antidepressant medication nearly doubled the rate of depression remission — 61.5% versus 33.3% with medication alone. Among those who achieved insomnia remission, 83% also achieved depression remission (Manber et al., 2008).

A meta-analysis in npj Digital Medicine confirmed digital CBT-i improves both insomnia and depressive symptoms, with a moderate effect for depression (SMD −0.42) and a large effect for sleep (SMD −0.76) — and higher adherence strengthened the effect (Lee et al., 2023). So the message is not “depression makes CBT-i pointless.” The message is that depression changes what a good treatment plan looks like:

• Assess and address depression at the same time as insomnia. Walking into CBT-i with unrecognized depression is the strongest modifiable risk factor for poor long-term outcomes. You don’t need to resolve depression first — both should be on the table from the start.
• Plan follow-up beyond the initial treatment block. An eight-session course is a starting point, not a finish line. If your baseline depression score is elevated, check-ins at three, six, and twelve months catch early relapse before it becomes entrenched.
• Work with a clinician who can treat both. Tip sheets and generic apps can’t adapt to the interaction between depression and insomnia in your case — especially given rural and northern access realities in Saskatchewan.

Good news for older adults

One encouraging finding: older age was associated with better treatment response, with lower anxiety and depression scores over time. The study didn’t isolate a mechanism, but the picture makes sense — more regular routines that align with CBT-i’s structure, fewer competing life demands, and strong motivation for health-related change. If you are an older adult considering CBT-i, the data suggest you are well positioned to benefit.

Should you screen for depression before starting CBT-i?

Yes — and this is not a formality. The PHQ-9 is a nine-item questionnaire that takes about two minutes, scoring 0–27. In the Huang study, nearly a quarter of participants entered treatment with severe depression (PHQ-9 ≥ 15) and another 20% with moderate depression — exactly the patients most likely to show attenuated gains and earlier relapse, and exactly the ones who benefit most from a depression-aware plan. Primary-care research points the same way: baseline depressive symptoms, not baseline insomnia severity, predicted who achieved remission after CBT-i (Michel et al., 2023).

At STG Health, the PHQ-9 is part of every insomnia intake. If your score is elevated, we adjust the plan — not by withholding CBT-i, but by building in concurrent mood monitoring, more frequent check-ins, and coordination with your prescribing physician when appropriate.

If CBT-i has not held for you, the answer is not “try harder”

If your gains didn’t last, the problem was probably not effort. Depression may have been part of the picture and not adequately addressed alongside the insomnia. That is fixable: depression is treatable, insomnia is treatable, and when both are treated together, outcomes for each improve. You do not need to figure this out alone.

Frequently asked questions

Does depression affect how well CBT-i works?

Yes, significantly. Baseline depression severity was the single strongest predictor of long-term CBT-i outcomes — stronger than anxiety or insomnia severity (Huang et al., 2026).

Can CBT-i help with depression, not just sleep?

Yes. Adding CBT-i to medication nearly doubled depression remission compared with medication alone (Manber et al., 2008).

Why do CBT-i gains sometimes fade after a year?

The 12-month drift is a documented pattern, particularly with elevated baseline depression. Booster sessions and planned follow-up are the most effective way to sustain gains.

Should I address my depression before starting CBT-i?

You don’t need to resolve depression first — but both should be assessed and monitored from the outset.

References

• Huang, X., et al. (2026). Long-term outcomes of mobile-delivered CBT-I in insomnia patients: A four-year follow-up study. Frontiers in Neuroscience.
• Lee, E., et al. (2023). Digital cognitive behavioral therapy for insomnia and comorbid depression and anxiety: A meta-analysis. npj Digital Medicine.
• Manber, R., et al. (2008). Cognitive behavioral therapy for insomnia enhances depression outcome in patients with comorbid major depressive disorder and insomnia. Sleep, 31(4), 489–495.
• Michel, F., et al. (2023). Predictors of CBT-I remission in primary care insomnia. Psychiatry Research.
• Muench, A., et al. (2022). Treatment adherence in cognitive behavioral therapy for insomnia. Journal of Sleep Research.

Ready to actually fix your sleep? SaskSleep delivers CBT-i-informed insomnia care across Saskatchewan via secure telehealth. Book your intake session or start with the free Sleep Starter Plan.