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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:16.0pt;font-weight:bold;">UNITED STATES</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:16.0pt;font-weight:bold;">SECURITIES AND EXCHANGE COMMISSION</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Washington,&nbsp;D.C. 20549</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:16.0pt;font-weight:bold;">FORM&nbsp;8-K</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Current Report Pursuant to</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Section 13 or 15(d) of the</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Securities Exchange Act of 1934</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Date of Report (Date of Earliest Event Reported):</font></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">October 22, 2013</font></b></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:20.0pt;font-weight:bold;">IRONWOOD PHARMACEUTICALS, INC.</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(Exact name of registrant as specified in its charter)</font></i></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Delaware</font></b></p>    </td>
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<p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">001-34620</font></b></p>    </td>
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<p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">04-3404176</font></b></p>    </td>   </tr>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(State or   other jurisdiction</font></i></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(I.R.S.   Employer</font></i></p>    </td>   </tr>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">of   incorporation)</font></i></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><i><font size="2" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(Commission   file number)</font></i></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><i><font size="2" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">Identification   Number)</font></i></p>    </td>   </tr>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">&nbsp;</font></b></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">301 Binney Street</font></b></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
<td width="32%" valign="top" style="padding:0in 0in 0in 0in;width:32.0%;">
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
<td width="32%" valign="top" style="padding:0in 0in 0in 0in;width:32.0%;">
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Cambridge,   Massachusetts</font></b></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:1.0pt;font-weight:bold;">&nbsp;</font></b></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">02142</font></b></p>    </td>   </tr>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(Address of   principal</font></i></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
<td width="32%" valign="top" style="padding:0in 0in 0in 0in;width:32.0%;">
<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
<td width="32%" valign="top" style="padding:0in 0in 0in 0in;width:32.0%;">
<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>   </tr>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">executive   offices)</font></i></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><i><font size="2" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>    </td>
<td width="32%" valign="top" style="padding:0in 0in 0in 0in;width:32.0%;">
<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>    </td>
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<p style="margin:1.0pt 0in .0001pt;"><i><font size="2" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>    </td>
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<p align="center" style="margin:1.0pt 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(Zip code)</font></i></p>    </td>   </tr>  </table>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">(617) 621-7722</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><i><font size="1" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">(Registrant&#146;s telephone number,</font></i></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><i><font size="1" face="Times New Roman" style="font-size:1.0pt;font-style:italic;">&nbsp;</font></i></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><i><font size="2" face="Times New Roman" style="font-size:10.0pt;font-style:italic;">including area code)</font></i></p>
<p style="margin:0in 0in .0001pt;text-align:justify;text-justify:inter-ideograph;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;text-align:justify;text-justify:inter-ideograph;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:</font></p>
<p style="margin:0in 0in .0001pt;text-align:justify;text-justify:inter-ideograph;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="2" style="font-size:10.0pt;"> Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)</font></p>
<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="2" style="font-size:10.0pt;"> Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)</font></p>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="2" style="font-size:10.0pt;"> Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))</font></p>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="2" style="font-size:10.0pt;"> Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))</font></p>
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<p style="margin:0in 0in .0001pt;text-align:justify;text-justify:inter-ideograph;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;text-align:justify;text-justify:inter-ideograph;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Item&nbsp;2.02 Results of Operations and Financial Condition.</font></b></p>
<p style="margin:0in 0in .0001pt;text-align:justify;text-justify:inter-ideograph;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">On October 22, 2013, Ironwood Pharmaceuticals, Inc. issued a press release containing an update on its recent business activities as well as those for the quarter ended September 30, 2013. A copy of the press release is furnished as Exhibit 99.1 and is incorporated herein by reference.</font></p>
<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">The press release is being furnished pursuant to Item 2.02 of this Current Report on Form 8-K and shall not be deemed &#147;filed&#148; for purposes of Section&nbsp;18 of the Securities Exchange Act of 1934, as amended (the &#147;Exchange Act&#148;) or otherwise subject to the liabilities of that Section, nor shall such document be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act except as shall be expressly set forth by specific reference in such filing.</font></p>
<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Item&nbsp;9.01 Financial Statements and Exhibits.</font></b></p>
<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">&nbsp;</font></p>
<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">(d)&#160;&#160; Exhibits.</font></p>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Exhibit&nbsp;No.</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Description</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">&nbsp;</font></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">99.1</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:1.0pt;">&nbsp;</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Ironwood Pharmaceuticals, Inc.   Press Release dated October 22, 2013</font></p>    </td>   </tr>  </table>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">SIGNATURES</font></b></p>
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<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.</font></p>
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<p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:11.0pt;font-weight:bold;">Ironwood   Pharmaceuticals, Inc.</font></b></p>    </td>   </tr>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Dated: October 22, 2013</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">/s/ Michael J. Higgins</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:11.0pt;">Title: &nbsp;&nbsp;Chief Operating Officer and Chief Financial   Officer</font></p>    </td>   </tr>  </table>
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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 8-K
Current Report Pursuant to
Section 13 or 15(d) of the
Securities Exchange Act of 1934
Date of Report (Date of Earliest Event Reported):
October 22, 2013
IRONWOOD PHARMACEUTICALS, INC.
(Exact name of registrant as specified in its charter)
Delaware
001-34620
04-3404176
(State or   other jurisdiction
(I.R.S.   Employer
of   incorporation)
(Commission   file number)
Identification   Number)
301 Binney Street
Cambridge,   Massachusetts
02142
(Address of   principal
executive   offices)
(Zip code)
(617) 621-7722
(Registrant's telephone number,
including area code)
Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:
o
Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)
o
Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)
o
Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))
o
Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))
Item 2.02 Results of Operations and Financial Condition.
On October 22, 2013, Ironwood Pharmaceuticals, Inc. issued a press release containing an update on its recent business activities as well as those for the quarter ended September 30, 2013. A copy of the press release is furnished as Exhibit 99.1 and is incorporated herein by reference.
The press release is being furnished pursuant to Item 2.02 of this Current Report on Form 8-K and shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act") or otherwise subject to the liabilities of that Section, nor shall such document be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act except as shall be expressly set forth by specific reference in such filing.
Item 9.01 Financial Statements and Exhibits.
(d)   Exhibits.
Exhibit No.
Description
99.1
Ironwood Pharmaceuticals, Inc.   Press Release dated October 22, 2013
SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
Ironwood   Pharmaceuticals, Inc.
Dated: October 22, 2013
By:
/s/ Michael J. Higgins
Name: Michael J. Higgins
Title:   Chief Operating Officer and Chief Financial   Officer