Some argue that THC-O is legal, under the 2018 Farm Bill, because the molecule is derived from legal hemp plants. However, opponents cite the 1986 Federal Analogue Act in claiming that any substance analogous to a Schedule I drug (like THC) would qualify, in turn, as a Schedule I drug.
As with products containing delta-8 THC and delta-10 THC, products with THC-O exist in the marginal legal space between hemp (which is legal nationwide) and cannabis (which is not). State regulators and legislators are currently playing whack-a-mole with the growing number of hemp-derived compounds, banning novel compounds only to see new derivatives take their place.
Until THC-O and other hemp derivatives come under a state-regulated system, consumers will need to weigh the risks and benefits of these compounds for themselves.