Objectives: To investigate the efficacy of the Thai Health Improvement Profile intervention for preventing clinically significant weight gain in people with early stage psychosis.

Methods: We undertook a randomised controlled trial from 10/2018 to 05/2021. Participants with early stage psychosis (<5 year duration)were recruited using convenience sampling from the caseloads of community psychiatric nurses in Thailand and randomly allocated to either the Thai Health Improvement Profile intervention or treatment as usual group following baseline assessment. Outcome assessors were blind to group allocation, whereas participants were not. Participants in the intervention group received three monthly (five in total) systematic health checks using the Thai Health Improvement Profile tool, which was used to develop a personal health plan in collaborationwith a family member/carer. Nurses supported participants to implement the health plan using behaviour change techniques derived from motivational interviewing. The treatment as usual group consisted of medication and psychosocial support, and no additional intervention was provided. The primary  outcomewasweight gain (defined as a greater or equal to 7 % increase inweight against baseline) within 1 year.

Results: Fifty-three participantswere allocated to the intervention and an equal number to the treatment as usual group. Primary outcome datawere available for 30 participants in each group at the 12month follow-up.We undertook an intention to treat analysiswithmultiple imputation (to handle themissing data) for the primary outcome. The treatment as usual group was found to have higher odds than the Thai Health Improvement Profile intervention group of gaining ≥7 % of baseline body weight (OR = 6.52; 95 % CI: 1.88–22.65, p = 0.004).

Conclusions: The Thai Health Improvement Profile interventionwas effective at preventing weight gain in people with early stage psychosis at one year, though attrition was relatively high. The results highlight the need for community mental health nurses to adopt a holistic approach, the potential benefits of conducting regular comprehensive health checks and the importance of involving familymemberswhen aiming to improve the physical health of people diagnosedwith early stage psychosis. A large definitive multi-site randomised controlled trial of the Thai Health Improvement Profile with a longer follow-up is now justified.