Often, the chemical structure of drugs is similar to brain chemicals or neurotransmitters. Similarity in structure allows them to be recognized by neurons and to alter normal brain messages. Illustrated above is THC, the active ingredient found in marijuana. It’s chemical structure is highly similar to anandamide, which is involved in a variety of functions including regulation of pain, appetite, memory, and mood.
As a result of scientific research, we know that addiction is a disease that affects both brain and behavior.