most medicine are safe as in they are excreted by the body quite fast normally in a day or so. Unless the patient dont follow recommended dosage or has problem with kidney and liver.

it is the duty of doctor to adjust the dosage of medicine according to age, sex, weight, and other condition of the patient.

as for patient with terminal illness its really up to the patient to receive treatment or not.

for normal sickness its better to take medicine as that will hasten recovery, prevent complications and less infect other people.

if patient has any doubt, just ask the doctor. patient has the right to know what they are taking.

issues i can think about medicine is that medicine (in general) might interfere with the process of evolution by saving both weak and thus saving the "bad" genes. these genes thus continue in the gene pool and slow or prevent further evolution.

also the rich takes more benefit from medicine than the poor, thus results in social imbalance between the rich and poor.