First, let's define the word "Endocrinology".
Endocrinology is the study of the endocrine glands. This endocrine gland secretes a messenger molecule known as hormone. So what is hormone? Hormone comes from the Greek word "hormon" which means to excite or to arouse activity. It is a substance of the body that sends out messages that can affect cells. Examples of these are Adenocorticotrophic hormone (ACTH) and Thyroid Stimulating Hormone (TSH).
Toxicology deals with the study of toxins that can become poisonous when it enters our body that will cause harm and later on it can cause some certain diseases or even death. It may occur through ingestion (which is the most common cause of poisoning) and inhalation.
Last but not the least,
Drug Testing is the process by which we detect if there is a prohibited drug intake (e.g cocaine [benzoylmethylecgonine], marijuana [cannabis]). This test is usually required for some application such as drivers license. Urine is the most common specimen for this test but hair, blood, sweat and saliva can also be used.