To be an analog a chemical must meet three criteria-
1 Be chemically similar (in structure) to a controlled substance
2 Have affects similar to the controlled substance
3 Be sold for human consumption
This last requirement was used as a loophole by a few enterprising guys who are now in a federal prison for most of the rest of their lives.
There are still enterprising guys in countries beyond the reach of the DEA which will send you some very interesting things.