Half the children were given growth hormone, half 'Puberty blockers' such as might be given in gender clinics.
They were all given puberty blockers - some were also given the growth hormone:
This randomized trial treated 30 adopted children with early puberty and short stature with either gonadotropin-releasing hormone agonist (GnRHa) alone or in combination with growth hormone (GH) for 3 y.
There was a drop in IQ across both groups, but both groups were given the puberty blockers. This doesn't mean that the drugs were a cause of this drop, but I'm surprised it wasn't seen as significant.