No, we cannot - at least not reliably. That's why, with a few exceptions like chemo drugs, clinical trials start by giving separate groups of healthy patients i

No, we cannot - at least not reliably. That's why, with a few exceptions like chemo drugs, clinical trials start by giving separate groups of healthy patients increasing doses of the drug until 50% of a test group can no longer tolerate the side effects, to establish a maximum dose for the rest of the trials. Deaths in these Phase 1 trials are not exactly an every day occurrence but it's enough of a risk that this phase is most often done under total medical supervision (i.e. the patients don't go home until their role in the trial is over). This is also the phase where doctors begin to collect data about the pharmacology of the drug, which is used to compare the animal models against in vivo to figure out how the effects diverge.