Can the human body produce THC?

Actually, the body DOES create its own form of THC.

This chemical is called Anandamide (AEA).

"...its structure was first described by Czech analytical chemist Lumír Ondřej Hanuš and American molecular pharmacologist William Anthony Devane in the Laboratory of Raphael Mechoulam, at the Hebrew University in Jerusalem, Israel in 1992."

-Wikipedia

The amount of anandamides we receive naturally is far below the amount that comes from consuming cannabis, however scientists have found no damage to the CB1 and CB2 receptors as a result of cannabis use.

Anandamide is thought to be an endogenous ligand for vanilloid receptors, which controls pain and inflammation.

Furthermore, because anandamide has been found to be involved in working memory, scientists are studying its roles in human behavior: eating, sleeping and pain relief.