UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

(Amendment No. 1)

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, 2023

(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).

Explanatory Note:

This Amendment No. 1 to the Schedule 13G (“Amendment No. 1”) relating to eFFECTOR Therapeutics Inc., a Delaware corporation (the “Company”), is being filed on behalf of the undersigned to amend the Schedule 13G filed with the Securities and Exchange Commission on February 14, 2022 (the “Schedule 13G”). This Amendment No. 1 is being filed to disclose that the Reporting Persons have ceased to be the beneficial owner of more than five percent of the outstanding shares of common stock, par value $0.001 (the “Common Stock”) of the Company. This Amendment No. 1 is the final amendment to the Schedule 13G and constitutes an exit filing for the Reporting Persons.

ITEM 1.

eFFECTOR Therapeutics Inc.

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

ITEM 2.

This Amendment No. 1 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 I Manager, LLC (“Co-Invest Manager”), and 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.

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

28202V 108

ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO §§ 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 Reporting Person of this Amendment No. 1 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 [X].

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, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: February 9, 2024

This Amendment No. 1 was executed by Sasha Keough on behalf of the entities and individual listed above pursuant to a Limited Power of Attorney, a copy of which is attached as Exhibit 2 hereto.

Exhibit 1

JOINT FILING AGREEMENT

This joint filing agreement (this “Agreement”) is made and entered into as of February 9, 2024, 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 I Manager, 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.

This Joint Filing Agreement was executed by Sasha Keough on behalf of the entities and individual listed above pursuant to a Limited Power of Attorney, a copy of which is attached as Exhibit 2 hereto.

Exhibit 2

LIMITED POWER OF ATTORNEY

Know all by these presents, that the undersigned hereby makes, constitutes and appoints Sasha Keough, Karen Narolewski-Engel, James Macadam, and Alexander M. Bowling, and each of them singly, as each of the undersigned’s true and lawful attorneys-in-fact with full power and authority as hereinafter described to:

1. execute for and on behalf of each of the undersigned individual and entities (each, a “Filer” and collectively, the “Filers”) (i) Forms 3, 4, and 5 (including amendments thereto) in accordance with Section 16(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the rules thereunder, (ii) Form 144 in accordance with Rule 144 under the Securities Act of 1933, as amended (the “Securities Act”), and (iii) Schedules 13D and 13G (including amendments thereto) in accordance with Sections 13(d) and 13(g) of the Exchange Act and the rules thereunder;

2. do and perform any and all acts for and on behalf of each of the Filers which may be necessary or desirable to complete and execute any such Form 3, 4, or 5 (including amendments thereto), Form 144, or Schedule 13D or 13G (including amendments thereto) and timely file such form with the United States Securities and Exchange Commission (the “SEC”) and any stock exchange or similar authority, including, but not limited to, executing a Form ID or Update Passphrase request for and on behalf of each of the undersigned and filing such applications with the SEC; and

3. take any other action of any type whatsoever in connection with the foregoing which, in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by, a Filer, it being understood that the documents executed by such attorney-in-fact on behalf of such Filer pursuant to this Limited Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve in such attorney-in-fact’s discretion.

Each of the Filers hereby grants to each attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes a Filer might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all the acts such attorney-in-fact, or such attorney-in-fact’s substitute or substitutes, shall lawfully do or cause to be done by virtue of this Limited Power of Attorney and the rights and powers herein granted. Each of the Filers acknowledges that each of the foregoing attorneys-in-fact, in serving in such capacity at the request of such Filer, is not assuming any of such Filer’s responsibilities to comply with Sections 13 or 16 of the Exchange Act or Rule 144 under the Securities Act.

This Limited Power of Attorney shall remain in full force and effect until a Filer is no longer required to file Forms 3, 4, and 5 (including amendments thereto), Form 144, and Schedules 13D and 13G (including amendments thereto) with respect to such Filer’s holdings of and transactions in securities, unless earlier revoked by such Filer in a signed writing delivered to each of the foregoing attorneys-in-fact. In addition, at such time as any attorney-in-fact resigns as attorney-in-fact by the execution of a written resignation delivered to each Filer, without any action on the part of the Filers, this Limited Power of Attorney shall be partially revoked solely with respect to such individual; such individual shall cease to be an attorney-in-fact under this Limited Power of Attorney; and the authority of the other attorneys-in-fact then existing hereunder shall remain in full force and effect.

[Signature page follows]

IN WITNESS WHEREOF, each of the undersigned has caused this Limited Power of Attorney to be executed as of this 12th day of December, 2022.