This study directly compared two popular psychedelic drugs, LSD and psilocybin (magic mushrooms), in 28 healthy volunteers. Researchers found that these substances produce very similar mental effects when given at equivalent doses, with the main difference being that LSD lasts longer. The study establishes that about 20 milligrams of psilocybin is roughly equivalent to 100 micrograms of LSD. These findings could help guide dosing for future psychiatric treatments using these psychedelics.