Delta 8 and Delta 9 have similar effects on the body through the endocannabinoid system. They both create effects of euphoria and a mental state more commonly defined as a "high." Both have relatively the same molecular structure. The difference is that the double bond for Delta 8 is on the 8th carbon while on the 9th for Delta 9; hence their names. The double bond is what gives THC the psychoactive quality.