Since you mentioned it, THC and tetrahydrocannabinol are the same... but different. I don't know enough about these kinds of diagrams to know what the differences are - but surely they should be the same?
The problem here is naming compounds - a name like "THC" is not precise enough to distinguish between these isomers. A more exact name could be "(–)-trans-Δ⁹-tetrahydrocannabinol" (from wikipedia).