A Ph.d is a doctorate. A person with the letters Ph.d after their name is called a Doctor, even if they did not study medicine.
People who study medicine are called medical students or medical professionals, depending on their level of training.
I guess you can call that person an athlete.
Micrologist
What is the study of codes
Astronomer
PHILOSOPHER
Smart person
An astronomer
A person who sells herbs to be used as medicine is typically called an herbalist or a herbal practitioner.
I think you call it a medicine tester
It is a vulcanologist.