UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

eFFECTOR Therapeutics, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

28202V 108

(CUSIP Number)

December 31, 2021

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

☐ Rule 13d-1(b)

☐ Rule 13d-1(c)

☒ Rule 13d-1(d)

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

Persons who respond to the collection of information contained in this form are not

required to respond unless the form displays a currently valid OMB control number.

ITEM 1.

eFFECTOR Therapeutics Inc. (the “Company”)

11120 Roselle Street, Suite A, San Diego, CA 92121

ITEM 2.

This Schedule 13G is being filed jointly by SR One Capital Fund I Aggregator, LP (“SR One Fund I”), SR One Capital Partners I, LP (“SR One CP I”), SR One Capital Management, LLC (“SR One Management”), SR One Co-Invest I, LLC (“SR One Co-Invest”), SR One Co-Invest Manager I, LLC (“Co-Invest Manager”), Simeon George (each, a “Reporting Person” and, together, the “Reporting Persons”), pursuant to an Agreement of Joint Filing filed herewith in accordance with Rule 13d-1(k)(1) under the Act.

SR One Fund I is owned and controlled by SR One Management, which is indirectly owned and controlled by Simeon George. SR One CP I serves as the general partner of SR One Fund I and SR One Management serves as the general partner of SR One CP I. Co-Invest Manager serves as the manager of SR One Co-Invest and SR One Management serves as the manager of Co-Invest Manager. Simeon George is the managing member of SR One Management.

Each of SR One CP I, Co-Invest Manager, SR One Management and Simeon George disclaims beneficial ownership of the securities held by SR One Fund I and SR One Co-Invest.

The principal business address of each Reporting Person is as follows:

985 Old Eagle School Road, Suite 511, Wayne, PA 19087

Delaware

Common Stock, par value $0.001 (the “Common Stock”)

28202V 108

ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO SS.240.13d-1(b) OR 240.13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A:

ITEM 4. OWNERSHIP.

The information in items 1 and 5 through 11 on the cover page for each Filer of this Schedule 13G is hereby incorporated by reference.

ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS.

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [ ].

ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON.

Not Applicable.

ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY.

Not Applicable.

ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP.

Not applicable.

ITEM 9. NOTICE OF DISSOLUTION OF GROUP.

Not Applicable.

ITEM 10. CERTIFICATIONS.

Not Applicable.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: February 11, 2022

The original statement shall be signed by each person on whose behalf the statement is filed or his authorized representative. If the statement is signed on behalf of a person by his authorized representative other than an executive officer or general partner of the filing person, evidence of the representative’s authority to sign on behalf of such person shall be filed with the statement, provided, however, that a power of attorney for this purpose which is already on file with the Commission may be incorporated by reference. The name and any title of each person who signs the statement shall be typed or printed beneath his signature.

Exhibit 1

AGREEMENT OF JOINT FILING

This joint filing agreement (this “Agreement”) is made and entered into as of January 11, 2022, by and among SR One Capital Fund I Aggregator, LP, SR One Capital Partners I, LP, SR One Capital Management, LLC, SR One Co-Invest I, LLC, SR One Co-Invest Manager I, LLC, and Simeon George.

The parties to this Agreement hereby agree to prepare jointly and file timely (and otherwise to deliver as appropriate) all filings on any Form 3, Form 4, Form 5 or Schedule 13D or Schedule 13G, and any and all amendments thereto and any other document relating thereto with respect to the beneficial ownership by each of the undersigned of the shares of common stock of eFFECTOR Therapeutics, Inc. (collectively, the “Filings”) required to be filed by them pursuant to the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Each party to this Agreement further agrees and covenants to the other parties that it will fully cooperate with such other parties in the preparation and timely filing (and other delivery) of all such Filings.

This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all of which together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the date first set forth above.