My brother has been taking prednisone250mg for 3years is that safe?

Are you sure?: 250 mg of prednisone is incredibly high doses particularly for three years. That would be highly undesireable. Nonetheless any prednisone for long periods - like months to years - is undesireable. It can cause weight gain, set one up for diabetes, worsening blood pressure, cause fluid retention, disrupt sleep, weaken bones, predispose one to infections and other things too!