UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

SCHEDULE 13G

(Rule 13d-102)

Information to be Included in Statements Filed Pursuant

to § 240.13d-1(b), (c) and (d) and Amendments Thereto Filed

Pursuant to § 240.13d-2

Under the Securities Exchange Act of 1934

(Amendment No.    )

Disc Medicine, Inc.

(Name of Issuer)

Common Stock, $0.0001

par value per share

(Title of Class of Securities)

254604101

(CUSIP Number)

February 15, 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 on 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, as amended (“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).

The calculation of beneficial ownership is based on (i) 18,882,850 shares of Common Stock issued and outstanding, as reported by the Issuer in its prospectus supplement filed with the Securities and Exchange Commission on February 14, 2023 and (ii) 1,046,227 shares of Common Stock to be issued upon the exercise of pre-funded warrants held by Bain Capital Life Sciences Opportunities III, LP, which reflects the Beneficial Ownership Blocker.

Item 1(a). Name of Issuer

The name of the issuer to which this filing on Schedule 13G relates is Disc Medicine, Inc. (the “Issuer”).

Item 1(b). Address of Issuer’s Principal Executive Offices

The principal executive offices of the Issuer are located at 321 Arsenal Street, Suite 101, Watertown, Massachusetts 02472.

Item 2(a). Name of Person Filing

This Schedule 13G is being filed by Bain Capital Life Sciences Opportunities III, LP, a Delaware limited partnership (the “Reporting Person”).

Bain Capital Life Sciences Investors, LLC, a Delaware limited liability company (“BCLSI”), is the manager of Bain Capital Life Sciences III General Partner, LLC, a Delaware limited liability company (“BCLS Fund III GP”), which is the general partner of Bain Capital Life Sciences Fund III, L.P., a Delaware limited partnership (“BCLS Fund III”), which is the sole member of Bain Capital Life Sciences Opportunities III GP, LLC, a Delaware limited liability company (“BCLS III Opportunities GP” and, together with the Reporting Person, BCLSI, BCLS Fund III GP and BCLS Fund III, the “Bain Capital Life Sciences Entities”), which is the general partner of the Reporting Person. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Reporting Person.

Item 2(b). Address of Principal Business Office or, if None, Residence

The principal business address for each of the Bain Capital Life Sciences Entities is 200 Clarendon Street, Boston, Massachusetts 02116.

Item 2(c). Citizenship

Each of the Bain Capital Life Sciences Entities are organized under the laws of the State of Delaware.

Item 2(d). Title of Class of Securities

The class of securities of the Issuer to which this Schedule 13G relates is Common Stock, $0.0001 par value per share (“Common Stock”).

Item 2(e). CUSIP Number

The CUSIP number of the Common Stock is 254604101.

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

If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution.

Item 4. Ownership

(a) Amount beneficially owned:

As of the date hereof, the Reporting Person holds 944,687 shares of Common Stock and pre-funded warrants to purchase 1,229,224 shares of Common Stock.

The Reporting Person is prohibited from exercising its pre-funded warrants if, as a result of such exercise, the Reporting Person would beneficially own more than 9.99% of the total number of shares of Common Stock then issued and outstanding immediately after giving effect to the exercise (the “Beneficial Ownership Blocker”). Accordingly, pursuant to Rule 13d-3 of the Act and the relationships described herein, the Reporting Person may be deemed to beneficially own 9.99% of the outstanding shares of Common Stock, representing 1,990,914 shares of Common Stock as of the date hereof.

The calculation of beneficial ownership is based on (i) 18,882,850 shares of Common Stock issued and outstanding, as reported by the Issuer in its prospectus supplement filed with the Securities and Exchange Commission on February 14, 2023 and (ii) 1,046,227 shares of Common Stock to be issued upon the exercise of pre-funded warrants held by the Reporting Person, which reflects the Beneficial Ownership Blocker.

(b) Percent of class:

See Item 4(a) hereof.

(c) Number of shares as to which the person has:

(i) Sole power to vote or to direct the vote:

0

(ii) Shared power to vote or direct the vote:

See Item 4(a) hereof

(iii) Sole power to dispose or to direct the disposition of:

0

(iv) Shared power to dispose or to direct the disposition of:

See Item 4(a) hereof

Item 5. Ownership of Five Percent or Less of a Class

Not applicable.

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 or Control Person

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

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the Issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURES

After reasonable inquiry and to the best of its knowledge and belief, the undersigned certifies that the information in this statement is true, complete and correct.