PROMISSORY NOTE

Exhibit 10.3

PROMISSORY NOTE

May 23, 2011

FOR VALUE RECEIVED, RADIUS HEALTH, INC., a Delaware Corporation located at the address stated below (“Borrower”), promises to pay to the order of OXFORD FINANCE LLC or any subsequent holder hereof (each, a “Lender”), the principal sum of THREE MILLION ONE HUNDRED TWENTY FIVE THOUSAND and 00/100 Dollars ($3,125,000.00) or, if less, the aggregate unpaid principal amount of all Term Loans made by Lender to or on behalf of Borrower pursuant to the Agreement (as hereinafter defined).  All capitalized terms, unless otherwise defined herein, shall have the respective meanings assigned to such terms in the Agreement.

This Promissory Note is issued pursuant to that certain Loan and Security Agreement, dated as of May 23, 2011, among Borrower, the guarantors from time to time party thereto, General Electric Capital Corporation, as agent, the other lenders signatory thereto, and Lender (as amended, restated, supplemented or otherwise modified from time to time, the “Agreement”), is one of the Notes referred to therein, and is entitled to the benefit and security of the Debt Documents referred to therein, to which Agreement reference is hereby made for a statement of all of the terms and conditions under which the loans evidenced hereby were made.

The principal amount of the indebtedness evidenced hereby shall be payable in the amounts and on the dates specified in the Agreement.  Interest thereon shall be paid until such principal amount is paid in full at such interest rates and at such times as are specified in the Agreement.  The terms of the Agreement are hereby incorporated herein by reference.

All payments shall be applied in accordance with the Agreement.  The acceptance by Lender of any payment which is less than payment in full of all amounts due and owing at such time shall not constitute a waiver of Lender’s right to receive payment in full at such time or at any prior or subsequent time.

All amounts due hereunder and under the other Debt Documents are payable in the lawful currency of the United States of America.  Borrower hereby expressly authorizes Lender to insert the date value as is actually given in the blank space on the face hereof and on all related documents pertaining hereto.

This Note is secured as provided in the Agreement and the other Debt Documents.  Reference is hereby made to the Agreement and the other Debt Documents for a description of the properties and assets in which a security interest has been granted, the nature and extent of the security interest, the terms and conditions upon which the security interest was granted and the rights of the holder of the Note in respect thereof.

Time is of the essence hereof.  If Lender does not receive from Borrower payment in full of any Scheduled Payment or any other sum due under this Note or any other Debt Document within 3 days after its due date, Borrower agrees to pay the Late Fee in accordance with the Agreement.  Such Late Fee will be immediately due and payable, and is in addition to any other costs, fees and expenses that Borrower may owe as a result of such late payment.

This Note may be voluntarily prepaid only as permitted under Section 2.4 of the Agreement.  After an Event of Default, this Note shall bear interest at a rate per annum equal to the Default Rate pursuant to Section 2.6 of the Agreement.

Borrower and all parties now or hereafter liable with respect to this Note, hereby waive presentment, demand for payment, notice of nonpayment, protest, notice of protest, notice of dishonor, and all other

notices in connection herewith, as well as filing of suit (if permitted by law) and diligence in collecting this Note or enforcing any of the security hereof, and agree to pay (if permitted by law) all expenses incurred in collection, including reasonable attorneys’ fees and expenses, including without limitation, the allocated costs of in-house counsel.

THIS NOTE SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS OF THE STATE OF NEW YORK.

No variation or modification of this Note, or any waiver of any of its provisions or conditions, shall be valid unless such variation or modification is made in accordance with Section 10.8 of the Agreement.   Any such waiver, consent, modification or change shall be effective only in the specific instance and for the specific purpose given.

IN WITNESS WHEREOF, Borrower has duly executed this Note as of the date first above written.