The legal threshold is the EUA.

Informed consent laws are more rigorous for volunteers in a medical experiment than for patients receiving an FDA approved product. EUA for unapproved products, however, are not categorized under experimental use.

Nevertheless, informed consent under EUA requires:

https://wwwnc.cdc.gov/eid/article/13/7/pdfs/06-1188.pdf

...both healthcare providers and their patients must be made aware that the product has been authorized for emergency use, must know the “significant known and potential benefits and risks” of emergency use of the product and extent to which such benefits and risks are unknown, and must be informed of any alternatives that may be available and their benefits and risks. Additionally, as a general rule, persons must be made aware of their right to refuse the product (or to refuse it for their children or others without the capacity to consent) and of the potential consequences, if any, of this choice.

The legal threshold is the EUA.

Informed consent laws are more rigorous for volunteers in a medical experiment than for patients receiving an FDA approved product. EUA for unapproved products, however, are not categorized under experimental use.

Nevertheless, informed consent under EUA requires:

https://wwwnc.cdc.gov/eid/article/13/7/pdfs/06-1188.pdf

...both healthcare providers and their patients must be made aware that the product has been authorized for emergency use, must know the “significant known and potential benefits and risks” of emergency use of the product and extent to which such benefits and risks are unknown, and must be informed of any alternatives that may be available and their benefits and risks. Additionally, as a general rule, persons must be made aware of their right to refuse the product (or to refuse it for their children or others without the capacity to consent) and of the potential consequences, if any, of this choice.