The FDA and the DEA have no connection to each other.
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.
The DEA enforces FDA regulations though through criminal and civil prosecution of those using otherwise DEA-legal and properly prescribed substances that are not FDA approved. Except for medical marijuana which had specific executive order to place state-licensed cannabis exempted from FDA regulation, a legally prescribed controlled substance becomes a DEA enforceable illegal substance when it is dispensed without FDA approval of the material.
The DEA enforces FDA regulations though through criminal and civil prosecution of those using otherwise DEA-legal and properly prescribed substances that are not FDA approved. Except for medical marijuana which had specific executive order to place state-licensed cannabis exempted from FDA regulation, a legally prescribed controlled substance becomes a DEA enforceable illegal substance when it is dispensed without FDA approval of the material.