Totally different. In the case of synthetic cannabinoids it is different chemicals that act on the same receptors as natural cannabinoids. Many of the ones that are really problematic,are full agonists instead of partial agonists so extreme effects that simply aren't possible with natural ones can happen. With mushrooms we have a mix of two chemicals that become the same thing once they hit the stomach. Synthetic psilocin and psilocybin (and also,the not naturally occuring but very similar 4 AcO-DMT) all produce what is essentially the same experience as eating mushrooms or drinking mushroom tea. I find the biggest difference is the pure chems are easier on the stomach.