You must mean vitamin D3. Lab produced vitamin D3 is indeed used as a rodenticide and it is also toxic to some other animals - but even with rats the toxic dose has to be very high. We recommend that people get their vitamin D3 from sunshine as much as possible. Sometimes, however, such things as time of year,
location, work schedule prevent people from getting natural vitamin D3, When such is the case, we recommend supplementing with D3 - but only in modest amounts. I have seen no convincing evidence that supplementing with minimal amounts of D3 is harmful.