Exhibit 10.5

SECOND AMENDMENT TO LOAN AND SECURITY AGREEMENT

THIS SECOND AMENDMENT TO LOAN AND SECURITY AGREEMENT (“Amendment”) is made and
dated as of August 11, 2014, and is entered into by and between CONCERT
PHARMACEUTICALS, INC., a Delaware corporation (the “Borrower”), and HERCULES
TECHNOLOGY GROWTH CAPITAL, INC., a Maryland corporation (“Lender”). Capitalized
terms used herein without definition shall have the meanings ascribed to such
terms in the Loan Agreement (defined below).

RECITALS

A. The Borrower and the Lender are party to that certain Loan and Security
Agreement dated as of December 22, 2011, as amended as of January 14, 2014 (the
“Loan Agreement”).

B. The parties desire to amend the Loan Agreement on the terms set forth herein.

AGREEMENT

NOW, THEREFORE, Borrower and Lender agree as follows:

1. Section 7.1(c) of the Loan Agreement is hereby amended and restated as
follows:

(c) as soon as practicable and in any event within ninety days (90 days) after
the end of each fiscal year, audited financial statements as of the end of such
year (prepared on a consolidated basis, if applicable), including balance sheet
and related statements of income and cash flows, and setting forth in
comparative form the corresponding figures for the preceding fiscal year,
certified by a firm of independent certified public accountants selected by
Borrower and reasonably acceptable to Lender, accompanied by an audit report
from such accountants which is unqualified as to scope of audit;

2. Section 7.1 of the Loan Agreement is hereby amended by deleting the final
paragraph thereof, and replacing it with the following:

“The executed Compliance Certificate may be sent to Lender via e-mail to
jbourque @herculestech.com. All Financial Statements required to be delivered
pursuant to clauses (a), (b) and (c) shall be sent via e-mail to
financialstatements@herculestech.com with a copy to jbourque@herculestech.com
provided that, (i) if e-mail is not available or sending such Financial
Statements via e-mail is not possible, they may be sent via facsimile to Lender
at: (866) 468-8916, attention Chief Credit Officer, and (ii) documents to be
furnished under Sections 7.1(b) and (c) may be furnished as set forth in the
following sentence. Documents required to be delivered under Sections 7.1(b),
(c) and (e) shall be deemed properly delivered on the date on which the Borrower
posts such documents, or provides a link thereto on the Borrower’s website, or
the date on which such documents are available on Edgar or other publicly
available website and Borrower notifies Lender by email of such availability.”

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3. The Compliance Certificate is hereby amended by deleting “180 days” and
replacing it with “90 days.”

4. Except as modified herein, the Loan Agreement remains unchanged and in full
force and effect. The Borrower hereby ratifies, confirms and reaffirms the terms
and conditions of the Loan Agreement and the Loan Documents, and all grants of
security by the Borrower to the Lender in connection therewith.

5. This Amendments shall be governed by, and construed and enforced in
accordance with, the laws of the Commonwealth of Massachusetts, excluding
conflict of laws principles that would cause the application of laws of any
other jurisdiction.

6. The Borrower represents that no Event of Default has occurred and is
continuing.

[Remainder of Page Intentionally Blank]

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IN WITNESS WHEREOF, Borrower and Lender have duly executed and delivered this
First Amendment to Loan and Security Agreement as of the day and year first
above written.

 

BORROWER:

 

CONCERT PHARMACEUTICALS, INC.

Signature:   /s/ Ryan Daws Print Name:   Ryan Daws Title:   Chief Financial
Officer

Accepted in Boston, Massachusetts:

 

LENDER:

 

HERCULES TECHNOLOGY

GROWTH CAPITAL, INC.

By:   /s/ Ben Bang Name:   Ben Bang Its:   Senior Council