Usually, protein supplements (e.g., whey protein) are used by athletes and body-builders.
Because isometric exercise like body-building increases the diastolic blood pressure in short-term 1, it is recommended to check for serum creatinine and Urea before supplementation (because it may accelerate renal function decline in people with mild renal insufficiency 2), along with check-ups every 6 months (it is my personal comment as a physician).
It is all because there are some researches stating that high amount of Urea due to the intake of protein supplement may promote kidney damage by chronically increasing the glomerular pressure and hyperfiltration 3 , 4 ,5.
Even recommended doses of creatine monohydrate supplementation may cause kidney damage; therefore, anybody using this supplement should be warned about this possible side effect, and their renal functions should be monitored regularly6.
Toxic hepatitis is another rare side effects of supplementation for body-builders, which warrants these check-ups 7.
However, it does not mean that high-protein intake necessarily damages the kidneys in all users 8.
Furthermore, interactions with other drugs should be noticed if the users have underlying diseases or they use other medications.