Exactly. Or even- no known hallucinogens synthesized by their canonical biochemical pathways by enzymes expressed from the host species genome.
The OG hallucinogen, ergot, is ingested by eating wheat. If one presumed that the substance is made by wheat, and mined the wheat genome, they would never find the genes for its synthesis, because the hallucinogen is made by mold growing on the wheat.
It’s very rare you can draw a strong conclusion from negative results.