UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Item 2.

Identity and Background

Item 2 is hereby supplemented to add the following:

Nordic may be deemed to be a member of a “group,” within the meaning of Section 13(d)(3) of the Act, comprised of Nordic and the other persons referred to on Schedule A attached to this Schedule 13D (the “Separately Filing Group Members”). It is the understanding of Nordic that the Separately Filing Group Members have filed or are filing separate Schedule 13Ds pursuant to Rule 13d-1(k)(2) under the Act. Schedule A attached to this Schedule 13D sets forth certain information concerning the Separately Filing Group Members, which information is based solely on the information contained in the Schedule 13Ds filed by the Separately Filing Group Members.

Item 3.

Source and Amount of Funds or Other Consideration

Item 3 is hereby amended and restated in its entirety as follows:

Pursuant to an Agreement and Plan of Merger dated April 25, 2011 (the “Merger Agreement”), by and among the Issuer (under its former name of MPM Acquisition Corp.), RHI Merger Corp., a Delaware corporation and wholly owned subsidiary of the Company (“MergerCo”), and Radius Health, Inc., a Delaware corporation (the “Former Operating Company”), MergerCo merged with and into the Former Operating Company, with the Former Operating Company remaining as the surviving entity and a wholly-owned operating subsidiary of the Issuer. This transaction is referred to as the “Merger.” The Merger was effective as of May 17, 2011, upon the filing of a certificate of merger with the Delaware Secretary of State.  At the effective time of the Merger (the “Effective Time”), the legal existence of MergerCo ceased and all of the shares of the Former Operating Company’s common stock, par value $.01 per share (the “Former Operating Company Common Stock”), and shares of the Former Operating Company’s preferred stock, par value $.01 per share (the “Former Operating Company Preferred Stock”), that were outstanding immediately prior to the Merger were cancelled and each outstanding share of Former Operating Company Common Stock outstanding immediately prior to the Effective Time was automatically converted into the right to receive one share of the Issuer’s Common Stock, par value $.0001 per share (the “Common Stock”) and each outstanding share of Former Operating Company Preferred Stock outstanding immediately prior to the Effective Time was automatically converted into the right to receive one-tenth of one share of the Issuer’s Preferred Stock, par value $.0001 per share (the “Preferred Stock”) as consideration for the Merger.  Each share of the Preferred Stock is convertible into ten (10) shares of the Common Stock.

Following the Merger on May 17, 2011, the Issuer’s Board of Directors approved a transaction pursuant to which the Former Operating Company merged with and into the Issuer, leaving the Issuer as

the surviving corporation (the “Short-Form Merger”). In connection with the Short-Form Merger, the Issuer relinquished its corporate name and assumed in its place the name “Radius Health, Inc.” The Short-Form and name change became effective on May 17, 2011, upon the filing of a Certificate of Ownership and Merger with the Delaware Secretary of State.

On November 18, 2011, pursuant to the terms of that certain Series A-1 Convertible Preferred Stock Purchase Agreement (as amended, the “Stock Purchase Agreement”), dated as of April 25, 2011, among the Issuer and the investors referenced therein (the “Investors”), the Issuer issued an aggregate of 263,178 shares (the “Stage II Series A-1 Shares”) of its Series A-1 Convertible Preferred Stock, par value $.0001 per share (the “Series A-1 Stock”), to the Investors.  Such shares were issued in connection with the consummation of the Stage II Closing contemplated by the Stock Purchase Agreement at a purchase price of $81.42 per share resulting in aggregate proceeds to the Issuer of $21,427,952.76.  On December 14, 2011, pursuant to the terms of the Stock Purchase Agreement, the Issuer issued an aggregate of 263,180 shares (the “Stage III Series A-1 Shares” and together with the Stage II Series A-1 Shares, the “Series A-1 Shares”) of its Series A-1 Stock, to the Investors.  Such shares were issued in connection with the consummation of the Stage III Closing contemplated by the Stock Purchase Agreement at a purchase price of $81.42 per share resulting in aggregate proceeds to the Issuer of $21,428,115.6.

Following the Merger, the Short-Form Merger and the transaction reported in this Amendment No. 1, and assuming the conversion of all issued and outstanding shares of preferred stock of the Issuer, Nordic (a shareholder of the Former Operating Company prior to the Merger and the Short-Form Merger) owns 64,430 shares of Common Stock issuable to Nordic upon the conversion of 6,443 shares of Issuer Series A-5 Preferred Stock.

Item 4.

Purpose of the Transaction

Item 4 is not amended.

Item 5.

Interest in Securities of the Issuer

Item 5 is hereby amended and restated in its entirety as follows:

(a)           Aggregate number of securities beneficially owned by Nordic: 64,430

Percent of Class:  0.3%.  This percentage is calculated based upon 21,400,279 shares of outstanding Common Stock being deemed issued and outstanding, which consists of: (i) 645,399 shares of Common Stock that are issued and outstanding and (ii) an aggregate of 20,754,880 shares of Common Stock issuable upon conversion of all shares of Preferred Stock outstanding as of December 14, 2011 following completion of the Stage III Closing contemplated by the Stock Purchase Agreement  (as defined in this Schedule 13D) as disclosed in the Issuer’s Information Statement on Schedule 14C, filed with the SEC on December 27, 2011, and as disclosed to the Reporting Person by the Issuer separately.

Nordic owns 64,430 shares, excluding shares held by any of the Separately Filing Group Members, as to which Nordic disclaims beneficial ownership.

(b)           Regarding the number of shares as to which Nordic has:

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

See Line 7 of cover sheet.

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

See Line 8 of cover sheet.

(iii)          sole power to dispose or to direct the disposition:

See Line 9 of cover sheet.

(iv)          shared power to dispose or to direct the disposition:

See Line 10 of cover sheet.

Schedule A attached to this Amendment No. 1 sets forth, as of the date hereof, the number of shares owned on an as-converted basis and the percentage of shares as calculated (a) based upon 21,400,279 shares of outstanding Common Stock being deemed issued and outstanding, which consists of: (i) 645,399 shares of Common Stock that are issued and outstanding and (ii) an aggregate of 20,754,880 shares of Common Stock issuable upon conversion of all shares of Preferred Stock outstanding as of December 14, 2011 following completion of the Stage III Closing contemplated by the Stock Purchase Agreement (as defined in this Schedule 13D) as disclosed in the Issuer’s Information Statement on Schedule 14C, filed with the SEC on December 27, 2011, and as disclosed to the Reporting Person by the Issuer separately, and (b) in accordance with Rule 13d-3(d)(1) promulgated under the Exchange Act. All information with respect to the Separately Filing Group Members is based solely on the information contained in the Schedule 13Ds filed by the Separately Filing Group Members or on information provided separately to the Reporting Person by the Issuer.

(c)           Nordic has not effected any transaction in the Common Stock of the Issuer during the last 60 days.

(d)           No other person is known to have the right to receive or the power to direct the receipt of dividends from, or any proceeds from the sale of, shares beneficially owned by Nordic.

(e)           Not Applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer

Item 6 is hereby amended and restated in its entirety as follows:

Nordic is a party to the Amended and Restated Stockholders’ Agreement dated May 17, 2011, as amended by Amendment No. 1, dated as of November 7, 2011, Amendment No. 2, dated as of November 7, 2011, and Amendment No. 3 dated as of December 15, 2011, by and among the Issuer and the stockholders party thereto, which is attached as Exhibit 10.2 to the Issuer’s Current Report on Form 8-K filed with the Securities and Exchange Commission on December 15, 2011 and incorporated by reference herein.

Item 7.

Material to be Filed as Exhibits

Item 7 of the Schedule 13D is amended and supplemented as follows:

Exhibit 3           Amended and Restated Stockholders’ Agreement dated May 17, 2011, as amended by Amendment No. 1, dated as of November 7, 2011, Amendment No. 2, dated as of November 7, 2011, and Amendment No. 3 dated as of December 15, 2011, by and among the Issuer and the stockholders party thereto (incorporated by reference from the Issuer’s Current Report on Form 8-K dated December 9, 2011 and filed with the Securities and Exchange Commission on December 15, 2011).

By:

/s/ Thomas Nielsen

Name: Thomas Nielsen

Title: Chief Financial Officer

Separately Filing Group Member(2)

Outstanding
Shares
(as converted)

Voting % of
Outstanding Shares

Beneficial
Ownership

MPM Bioventures III, L.P.

302,750

1.4

%

31.9

%

MPM Bioventures III-QP, L.P.

4,502,870

21.0

%

87.5

%

MPM Bioventures III GMBH & Co. Beteiligungs KG

380,540

1.8

%

37.1

%

MPM Bioventures III Parallel Fund, L.P.

135,960

0.6

%

17.4

%

MPM Asset Management Investors 2003 BVIII LLC

87,160

0.4

%

11.9

%

MPM Bio IV NVS Strategic Fund, L.P.

2,987,790

14.0

%

82.2

%

The Wellcome Trust Limited, as Trustee of the Wellcome Trust

2,868,910

13.4

%

81.6

%

HealthCare Ventures VII, L.P.

2,292,053

10.7

%

80.3

%

OBP IV — Holdings LLC

1,837,693

8.6

%

74.5

%

mRNA II - Holdings LLC

18,411

0.1

%

2.8

%

Brookside Capital Partners Fund, L.P.

1,228,200

5.6

%

65.6

%

BB Biotech Growth N.V.

1,228,200

5.7

%

65.6

%

Ipsen Pharma SAS

173,260

0.8

%

21.2

%

All other holders of common stock and preferred stock

2,276,818

10.6

%

96.2

%