One study found that puberty blockers did not alleviate negative thoughts in children with gender dysphoria.
A British study  found that puberty blockers used to treat children aged 12 to 15 who have severe and persistent gender dysphoria had no significant effect on their psychological function, thoughts of self-harm, or body image.
However, as expected, the children experienced reduced growth in height and bone strength by the time they finished their treatment at age 16.
 Carmichael, P., Butler, G., Masic, U., Cole, T. J., De Stavola, B. L., Davidson, S., Skageberg, E. M., Khadr, S., & Viner, R. M. (2021). Short-term outcomes of pubertal suppression in a selected cohort of 12 to 15 year old young people with persistent gender dysphoria in the UK. PLOS ONE 16 (2). [Link]