Small Business FDA User Fee Adjustment Act of 2021 This bill reduces and waives certain fees related to marketing certain over-the-counter (OTC) drugs for businesses with fewer than 500 employees, including employees of affiliates. Starting in FY2022, the Food and Drug Administration (FDA) must waive the fee for the first OTC monograph order request from such a business. (Generally, an OTC monograph order request is a request for the FDA to evaluate whether a nonprescription drug meets certain standards.) The fee for each subsequent OTC monograph order request for such a business shall be 25% of the amount otherwise owed. For such a business, the FDA must also reduce the annual OTC monograph drug facility fee to 25% of the amount otherwise owed. (Generally, such a facility is engaged in the manufacturing or processing of an OTC monograph drug.)