Summary: This is the published protocol for DIAMONDS, a planned two-arm individually randomised controlled trial in NHS mental health trusts in England. It aims to recruit 380 adults with type 2 diabetes and severe mental illness and will compare a co-designed supported self-management programme against treatment as usual, with the difference in HbA1c at 12 months as the primary outcome. No efficacy, glycaemic, or cost-effectiveness results are reported, because the trial had not yet read out when the protocol was published.
PICO Summary
| Element | Detail |
|---|---|
| Population | Planned n = 380 adults (aged 18 years or older) with type 2 diabetes and severe mental illness (schizophrenia, bipolar disorder, schizoaffective disorder, psychosis or severe depression); multicentre, individually randomised controlled trial across NHS mental health trusts in England. |
| Intervention | DIAMONDS programme: one-to-one sessions with a trained DIAMONDS Coach over six months covering goal setting, action planning and diabetes self-management education, supported by a paper-based workbook and an optional digital application. Allocation 1:1, so approximately 190 participants planned per arm. |
| Comparison | Treatment as usual, with participants able to be offered NICE-recommended generic diabetes self-management education in line with routine practice; approximately 190 participants planned per arm. |
| Outcome | Pre-specified primary outcome: between-group difference in glycated haemoglobin (HbA1c) at 12 months post-randomisation. Secondary outcomes include physical and mental health measures, diabetes complications and physical activity, plus economic and process evaluations. No effect estimates, 95% confidence intervals, p-values or ARR/NNT are available, because this is a protocol and no trial results have been reported. Registered as ISRCTN22275538. |
Expert Commentary
The verdict here is straightforward: this is a protocol, not a results paper, so nothing about whether DIAMONDS works can yet be concluded. The document is a methodological blueprint, and it is a careful one. The clinical question is genuinely important, because type 2 diabetes is two to three times more common in people with severe mental illness, and conventional self-management programmes are rarely designed for this group. The planned design is a strength: individual randomisation, a multicentre setting, a defined six-month coach-delivered intervention, and a pre-specified primary outcome of HbA1c at 12 months, all registered prospectively. The main limitation worth weighing is one shared by all behavioural trials of this type. The intervention cannot be blinded, so participants and coaches know their allocation, which can bias self-reported secondary outcomes; the objective HbA1c primary endpoint partly offsets this concern. Sponsorship appears academic and publicly funded rather than industry-driven, and no implausibly strong effects are claimed because no effects are claimed at all. Can I use this with my patients? Not yet. There is no efficacy or safety signal to act on, and clinicians should await the trial results rather than infer benefit from the rationale. I would watch for the primary outcome publication under ISRCTN22275538 before changing any practice.
References
O’Carroll GC, Brown JVE, Carswell C, et al. DIAMONDS-a diabetes self-management intervention for people with severe mental illness: protocol for an individually randomised controlled multicentre trial. BMJ Open. 2025;15(3):e090295. doi:10.1136/bmjopen-2024-090295