Keep in mind, when Hoffman reported his first LSD experience at 250 micrograms, his colleagues repeatedly asked him if he was SURE he had his measurement right. It seemed an absurdly small dose at the time. I'm open to the idea of something being active at less than one microgram, incredible though it would be. The absolute lightest, unnoticeable except to rigorous scientific testing, effects of LSD begin around 7 micrograms.
Shulgin always began at 1 microgram for this very reason, though I think the next jump after that was to 10 micrograms, and then to 100. Assuming the molecule was extremely potent, and the dosage response curve very steep, the worst that could happen would be he tripped really hard on an unknown compound for an unknown length of time. That he's alive today after testing thousands of new compounds seems to suggest his method worked.