5. Comorbidities & Impact

Psychiatric comorbidities

• Depression: a nationwide Taiwanese cohort found CH patients had a 5.6-fold increased hazard of developing depression compared to controls (aHR 5.6, 95% CI 3.0–10.6), with the annual number of cluster bouts itself predicting depression risk (aHR 3.8 per bout) peer-reviewed47. Another French cohort found depression in 43% of chronic CH patients peer-reviewed48.
• Anxiety: a multicentre registry found moderate-to-severe anxiety in 38.2% and moderate-to-severe depression in 34.6% of CH patients during active bouts, both dropping sharply during remission (e.g. PHQ-9 depression score falling from 6.1±5.0 in-bout to 1.8±2.4 in remission) — showing these symptoms are substantially state-dependent on bout activity, not fixed traits peer-reviewed49. Co-existing migraine massively amplifies this risk (aOR for depression up to 16.88 vs controls) peer-reviewed49.
• Suicidality — “the suicide headache”: CH has carried this nickname since B.T. Horton’s early descriptions peer-reviewed50. Findings are more nuanced than the nickname suggests. A large 2025 systematic review/meta-analysis found the overall suicidal risk in CH is not clearly elevated above general-population rates (suicidal ideation ~8.0% overall vs 5.2% in non-specialised comparison groups), but risk is markedly elevated specifically during attacks (ictal) and among patients seen in specialised headache clinics, where severity is higher peer-reviewed51. A study of 175 patients in-bout found passive suicidal ideation in 64.2% during attacks, versus only 4.0% interictally and 0% between bouts — suicidality in CH is overwhelmingly attack-linked, not a constant background state peer-reviewed52. Separately, a case-control study found CH patients had double the odds of lifetime suicidal ideation versus matched controls, and that this was best predicted by demoralization rather than depression itself peer-reviewed50. Some surveys report far higher lifetime figures — one large US CH survey found 55% had experienced suicidal thoughts and 2% had attempted suicide peer-reviewed48 — a notable divergence from the 2025 meta-analysis’s more moderate estimate, likely reflecting differences between clinic-referred/self-selected survey samples and population-representative cohorts. This divergence is presented as an open, unresolved tension rather than resolved. (Editor’s note: the full set of suicidality figures, including the population-level registry tension, is in Part III, §4.8; psychological-burden context is in Part I, §2.6.)
• A large multi-headache-type study found TAC patients overall (CH included) had more than double the risk of completed suicide (aHR 2.40) compared with headache-free controls peer-reviewed53.

Sleep and physical comorbidities

OSA (detailed in Section 4) and lifestyle-related disease are both elevated: the Danish Cluster Headache Survey found current or past smoking prevalence of 48.3% in CH patients vs 9.0% in controls, alongside excess prevalence of other lifestyle-related comorbid diseases peer-reviewed37.

Quality of life and employment impact

• A large European Migraine and Headache Alliance (EMHA) survey of 1,500 CH patients across the EU (2019) found 29% of chronic CH patients had prematurely exited the workforce (14% of the full sample); 22.5% reported being unfit for paid work due to CH; 12.7% had lost one job and 8% had lost more than one; and patients missed an average of 14 work days in the prior 3 months (19.8 days for chronic CH vs 4 days for episodic) [CITIZEN-SCIENCE/PEER-REVIEWED survey]54. 75% overall (90% of chronic CH patients) reported career interference peer-reviewed54.
• A validated CH-specific quality-of-life scale (the CHQ) has been developed from 406 patients in England, reflecting growing recognition that generic headache QoL tools understate CH’s distinct burden peer-reviewed55.
• A Korean prospective study specifically examined employment status, job type, sick leave and productivity loss in CH patients, reinforcing the EU findings with a separate national dataset peer-reviewed55.
• Spain’s national health system data show a similarly steep access-to-care problem underlying the employment burden: Spanish Society of Neurology reporting states diagnostic and treatment delays translate directly into avoidable years of unmanaged disability before patients reach appropriate care peer-reviewed76.