This is because the data shows what is being prescribed to people registered with Welsh GP practices and this activity is monitored and influenced by health boards.
Y rheswm am hyn yw bod y data’n dangos beth sy’n cael ei roi ar bresgripsiwn i bobl sydd wedi cofrestru â meddyg teulu yng Nghymru a chaiff y gweithgarwch hwn ei fonitro a’i lywio gan fyrddau iechyd.