Aim: Long-acting injectable (LAI)antipsychotics are often used in psychosis to assist with medication compliance and relapse prevention, although the weight gain and metabolic effects in young people are yet to be examined. This study examined the long-term effects of aripiprazole and paliperidone in LAI formulation on weight gain and metabolic parameters in young people with early episode psychosis. Methods: Weight gain and other metabolic effects of aripiprazole and paliperidone in LAI formulation were examined in 59 young people with early episode psychosis over a 12-month period. Changes in outcome measurements were examined at baseline and 3 monthly intervals. Results: The results showed that both aripiprazole and paliperidone were associated with time-dependent increases in weight. At 12 months, weight increased by an average of 7% (6 kg) with both aripiprazole and paliperidone relative to the baseline, and the percentage of overweight or obese people increased from 33% to 60%. There was no advantage of aripiprazole compared to paliperidone with regards to weight change, although aripiprazole was associated with lower triglycerides and prolactin levels. Conclusions: Both LAI medications were associated with substantial weight increases over time. These results build on emerging evidence showing that aripiprazole is not weight neutral in young people. Our recommendation is that weight-management programs should be offered from the start of medication initiation.