Guidelines on prescribing metformin in the context of antipsychotic use indicate that metformin can be considered for people who develop metabolic side effects such as weight gain and elevated blood glucose related to antipsychotic treatment, particularly to mitigate or treat antipsychotic-induced diabetes or prediabetes.
Antipsychotic medication initiation and initial physical health monitoring (including glucose and HbA1c) should occur under secondary care supervision, with the secondary care team responsible for at least the first 12 months or until the person's condition stabilises. After this, ongoing monitoring including metabolic parameters may be transferred to primary care under shared care arrangements.
Metformin is primarily indicated as first-line pharmacotherapy for type 2 diabetes and should be titrated gradually to minimise gastrointestinal side effects. Starting metformin in primary care is appropriate when the diagnosis of diabetes or prediabetes related to antipsychotic use has been established, especially after initial stabilisation and monitoring by secondary care.
This means that metformin initiation can be done in primary care, particularly when there is a clear indication of impaired glucose control or diabetes following antipsychotic use, provided there is suitable monitoring and shared care arrangements are established with secondary mental health services.