Table 4.
Subgroup analyses to explore potential causes of heterogeneity among included studies
| Outcome | Subgroups | Between group heterogeneity | Effect size with confidence intervals and heterogeneity (I2) per subgroup | Conclusion |
|---|---|---|---|---|
| Change in depression scores | Type of depression: primary or secondary | Significant (P=0.002) | Primary: Hedges’ g=0.84 (95% CI 0.07 to 1.61, I2=79.9%) Secondary: Hedges’ g=3.25 (95% CI 0.97 to 5.53, I2=79.1%) |
The effect size for reduction in depression post-intervention is considerably larger in secondary depression studies, but both subgroups contain considerable statistical heterogeneity suggesting factors other than depression type likely contribute to the observed heterogeneity |
| Change in depression scores | Depression measure: MADRS, QIDS, or BDI | Significant (P=0.001) | MADRS: Hedges’ g=1.18 (95% CI −1.36 to 3.73, I2=89.6%) QIDS: Hedges’ g=0.53 (95% CI 0.03 to 1.02, I2=0.0%) BDI: Hedges’ g=3.25 (95% CI 0.97 to 5.53, I2=79.1%) |
Studies using the patient reported QIDS and BDI questionnaires significantly favoured psilocybin, whereas MADRS studies did not The MADRS and BDI subgroups display considerable heterogeneity, whereas the QIDS subgroup did not |
| Change in depression scores | Psilocybin dosage: 10-15 mg or 20-25 mg | Not significant (P=0.26) | 10-15 mg: Hedges’ g=1.10 (95% CI −0.43 to 2.62, I2=86.9%) 20-25 mg: Hedges’ g=2.10 (95% CI 0.18 to 4.02, I2=92.2%) |
The two dosage groups did not appear to differentially affect the primary outcome, change in depression scores. Superior effect sizes seen in the higher dosage group should thus be interpreted with caution |
| Change in depression scores | Time of assessment post-psilocybin: 2-4 weeks or 4-8 weeks | Not significant (P=0.28) | 2-4 weeks: Hedges’ g=1.21 (95% CI 0.19 to 2.24, I2=82.1%) 4-8 weeks: Hedges’ g=2.62 (95% CI −2.66 to 7.90, I2=96.1%) |
The two time to assessment groups did not appear to differentially affect the primary outcome, change in depression scores. Superior effect sizes seen in the group assessed at 2-4 weeks should thus be interpreted with caution |
| Response rate | Type of depression: primary or secondary | Not significant (P=0.24) | Primary: risk ratio 1.79 (95% CI 0.88 to 3.64, I2=31.0%) Secondary: risk ratio 2.63 (95% CI 0.95 to 7.29, I2=0.0%) |
The likelihood of treatment response was not substantially affected by type of depression |
| Remission rate | Type of depression: primary or secondary | Not significant (P=0.92) | Primary: risk ratio 2.68 (95% CI 1.27 to 5.63, I2=0.0%) Secondary: risk ratio 2.79 (95% CI 0.60 to 12.88, I2=10.2%) |
The likelihood of remission was not substantially affected by type of depression |
I2=measure of heterogeneity.
BDI=Beck depression inventory; CI=confidence interval; MADRS=Montgomery-Åsberg depression rating scale; QIDS=quick inventory of depressive symptomatology.