A carcinogen is a cancer causing substance.
Carcinogen
The medical term for a foreign substance is "antigen." An antigen is any substance that the immune system identifies as foreign and triggers an immune response.
Keratin
antibiotic
Soporific is the medical and common term meaning pertaining to something that produces sleep.
Allergen
It is called bilirubin.
"Placebo". Alternatively, "homeopathy".
Bioavailability
analgesic
A pediculocide kills lice. It is a class of insecticides.
The substance injected during an angiography is called radionuclide.
Syncope is the medical term meaning fainting.