Final answer:
The body's natural ability to protect itself against harmful substances is known as the immune response, which is a defense mechanism designed to recognize and eliminate potential threats to the body. This response includes recognizing and eliminating harmful drugs.
Step-by-step explanation:
The body's and brain's natural ability to protect itself against harmful substances is known as the immune response. This response is a defense mechanism designed to recognize and eliminate potential threats to the body. One example of this is an allergy, which occurs when the immune system mistakenly identifies a harmless protein as harmful and triggers a response. So, in the case of drugs, the immune system can also mount a response to protect the body from substances that it perceives as harmful.