Interesting that the drug enforcement administration can make it illegal to buy something as a chemical. Their name would suggest that they're merely the enforcement arm of the FDA regarding drugs.
The DEA is a law enforcement agency that aims to fight illegal drug trafficking. the FDA is regulatory agency that aims to ensure the food and medicine legally sold in the US is safe.
If you are out there using e.g some experimental cancer drug that hasn't been FDA approved yet, the DEA isn't going to stop you. Their mission is to stop recreational use of drugs that get you high.
They are not going to give a shit about most experimental cancer drugs because they're not controlled substances.