Final answer:
The psychoactive compound in marijuana responsible for its 'high' is THC, which affects mood and consciousness. THC is used medically in FDA-approved drugs for certain treatments, while the legal status of marijuana varies by location.
Step-by-step explanation:
The main psychoactive chemical in marijuana that is responsible for its altering effects on the brain is known as THC (tetrahydrocannabinol). THC is one of over 200 chemicals found in marijuana, but it is particularly significant because it affects mood and consciousness, leading to the 'high' associated with marijuana use. The FDA has approved medications that contain THC for medical purposes such as treating nausea from chemotherapy and stimulating appetite in AIDS patients. Cannabis status varies across different jurisdictions, with some places allowing its use for recreational and/or medical purposes.