Many psychoactive molecules are also structurally very similar to other hormones, and molecules produced for other aspects of biological function. Take a look at NN-DMT and Melatonin:

https://en.wikipedia.org/wiki/N,N-Dimethyltryptamine

https://en.wikipedia.org/wiki/Melatonin

Just a slight mutation, or even biological synthesis under non-ideal conditions could easily result in synthesizing one or the other via the same pathway.