Heading 2938 requires that the article be a chemically defined glycoside compound — natural or synthetic — or a derivative thereof. Crude plant extracts that are not chemically defined single compounds typically fall under headings for vegetable extracts or other natural products. If the glycoside has been isolated and is chemically pure or of defined composition, 2938 is the appropriate heading; consult CBP for borderline botanical preparations.

Yes, cardiac glycosides including digoxin fall within the residual subheading 293890 when traded as bulk chemical substances. If formulated into a finished dosage form, they would instead be classified under the medicaments headings. FDA drug import requirements apply to cardiac glycoside APIs.