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                                                                    Exhibit 14.1

                           CUBIST PHARMACEUTICALS, INC
                              AMENDED AND RESTATED
                           CODE OF CONDUCT AND ETHICS
                          EFFECTIVE SEPTEMBER 15, 2003

INTRODUCTION

     This Code of Conduct and Ethics (this "Code") covers a wide range of
business practices and procedures. It does not cover every issue that may arise,
but it sets out basic principles to guide all employees of Cubist
Pharmaceuticals, Inc. (the "Company"). All of our employees must conduct
themselves accordingly and seek to avoid even the appearance of improper
behavior. This Code should also be provided to and followed by the Company's
agents and representatives, including consultants.

     If a law conflicts with a policy in this Code, you must comply with the
law; however, if a local custom or policy conflicts with this Code, you must
comply with the Code. If you have any questions about these conflicts, you
should seek advice from: (i) your Vice President, (ii) any director-level or
higher employee in Human Resources, (iii) any director-level or higher employee
in the Law Department.

     If you wish to report a violation or suspected violation of this Code, you
can contact the Company's Corporate Responsibility Hotline, which is
781-860-8600. The head of Human Resources will promptly investigate such
reports.

     If you wish to report ANONYMOUSLY a violation or suspected violation of
this Code, including, but not limited to, those: (i) relating to accounting,
internal accounting controls, or auditing matters or (ii) by one or more of the
Company's Executive Officers, you can contact the Company's CONFIDENTIAL
Corporate Responsibility Hotline, which is 617-241-1456. The Company's Internal
Auditors will promptly investigate all reports to the Confidential Corporate
Responsibility Hotline and, if after investigation, the Internal Auditors
determine that further action is necessary, they will report their findings to
the Audit Committee.

     A GOOD BASIS FOR DECIDING WHEN TO GET ADVICE IS TO ASK WHETHER THE CONDUCT
MIGHT BE EMBARRASSING TO THE COMPANY OR THE EMPLOYEES INVOLVED IF THE DETAILS
WERE FULLY DISCLOSED TO THE PUBLIC BY THE MEDIA.

     Those who violate the standards in this Code will be subject to
disciplinary action, up to and including termination.

1.   COMPLIANCE WITH LAWS, RULES AND REGULATIONS

     Obeying the law, both in letter and in spirit, is the foundation on which
this Company's ethical standards are built. All employees must respect and obey
the laws of the jurisdictions in which we operate. Although not all employees
are expected to know the details of these

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laws, it is important to know enough to determine when to seek advice from: (i)
your Vice President, (ii) any director-level or higher employee in Human
Resources, or (iii) any director-level or higher employee in the Law Department.

     The Company holds information and training sessions and has put in place
various policies and standard operating procedures in order to promote
compliance with laws, rules and regulations, including insider-trading laws.
Each department head is responsible for ensuring that his/her employees attend
all mandatory training sessions that are related to compliance with laws, rules
and regulations.

2.   CONFLICTS OF INTEREST

     All employees are expected to make decisions in the best interest of the
Company, and not for personal gain. Therefore, all employees are required to
avoid "conflicts of interest."

     A "conflict of interest" exists when a person's private interest interferes
in any way with the interests of the Company. A conflict situation can arise
when an employee, officer, or director takes actions or has interests that may
make it difficult to perform his or her Company work objectively and
effectively. Conflicts of interest may also arise when an employee, officer or
director, or members of his or her family, receives improper personal benefits
as a result of his or her position in the Company. Loans to, or guarantees of
obligations of, employees and their family members may create conflicts of
interest.

     It is almost always a conflict of interest for a Company employee to work
simultaneously for a competitor, customer, or supplier. You are not allowed to
work for a competitor as a consultant or board member. The best policy is to
avoid any direct or indirect business connection with our customers, suppliers,
or competitors, except on our behalf.

     Conflicts of interest are prohibited as a matter of Company policy, except
if approved by the Board of Directors on a case-by-case basis. Conflicts of
interest may not always be clear-cut, so if you have a question, you should seek
advice from: (i) your Vice President, (ii) any director-level or higher employee
in Human Resources, or (iii) any director-level or higher employee in the Law
Department. Any employee who becomes aware of a conflict or potential conflict
should bring it to the attention of: (i) his or her Vice President, (ii) any
director-level or higher employee in Human Resources, or (iii) any
director-level or higher employee in the Law Department.

3.   INSIDER TRADING

     Employees who have access to confidential information are not permitted to
use or share that information for stock trading purposes or for any other
purpose except the conduct of our business. All non-public information about the
Company should be considered confidential information. To use non-public
information for personal financial benefit or to "tip" others who might make an
investment decision on the basis of this information is not

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only unethical but also illegal. If you have any questions, please refer to your
copy of the Company's Amended and Restated Policy on Insider Trading and
Confidentiality, and then ask the Law Department.

4.   CORPORATE OPPORTUNITIES

     Employees, officers, and directors are prohibited from exploiting for their
personal advantage opportunities that are discovered through the use of
corporate property, information, or position without the consent of the Board of
Directors. No employee may use corporate property, information, or position for
improper personal gain, and no employee may compete with the Company directly or
indirectly. Employees, officers, and directors owe a duty to the Company to
advance its legitimate interests when the opportunity to do so arises.

5.   COMPETITION AND FAIR DEALING

     We seek to outperform our competition fairly and honestly. We seek
competitive advantages through superior performance, never through unethical or
illegal business practices. Stealing proprietary information, possessing trade
secret information that was obtained without the owner's consent, or inducing
such disclosures by past or present employees of other companies is prohibited.
Each employee should endeavor to respect the rights of and deal fairly with the
Company's customers, suppliers, competitors, and employees. No employee should
take unfair advantage of anyone through manipulation, concealment, abuse of
privileged information, misrepresentation of material facts, or any other
intentional unfair-dealing practice.

     Drug development is highly competitive, and it is the policy of the Company
to compete aggressively, but fairly. A major part of this commitment to compete
fairly is a commitment to abide fully by the antitrust laws. In general, these
complex laws prohibit any form of agreement or understanding -- whether formal,
informal, express, or implied -- that unreasonably reduces competition and
business rivalry. Our commitment in this regard also prohibits any unfair or
untrue disparagement of a Company competitor.

     Absent compelling circumstances, the company should select all vendors and
contractors on the basis of written competitive bids.

     The purpose of business entertainment and gifts in a commercial setting is
to create good will and sound working relationships, not to gain unfair
advantage with customers. Gifts or entertainment should not ever be offered,
given, provided or accepted by any Company employee, family member of an
employee or agent unless it: (1) is not a cash gift, (2) is consistent with
customary business practices, (3) is not excessive in value, (4) cannot be
construed as a bribe or payoff,(5) does not violate any laws or regulations, and
(6) is offered in compliance with applicable SOPs. You can also refer to the
"PhRMA Code" for additional guidance (copies of which are available from the Law
Department). Please seek advice from: (i) your Vice President, (ii) any
director-level or higher employee in Human Resources, or (iii)

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any director-level or higher employee in the Law Department, regarding any gifts
or proposed gifts which you are not certain are appropriate.

     It is the policy of the Company to comply with health care "fraud and
abuse" laws. This includes Federal and State anti-kickback laws that prohibit
offering or giving kickbacks or other improper inducements to those who may be
in a position to purchase or prescribe (or to arrange for or recommend the
purchase or prescription of) our products. Any arrangements with healthcare
customers (including but not limited to the provision of gifts, grants, and
business courtesies) should be reviewed to ensure compliance with applicable
laws, Company policies, and SOPs, which are available from the Law Department.

6.   DISCRIMINATION AND HARASSMENT

     The diversity of the Company's employees is a tremendous asset. We are
firmly committed to providing equal opportunity in all aspects of employment and
will not tolerate any discrimination or harassment of any kind. Please refer to
Cubist's "Anti-Harassment Policy" and "Policy Against Sexual Harassment in the
Workplace" for additional information and guidance.

7.   HEALTH AND SAFETY

     The Company strives to provide each employee with a safe and healthful work
environment. Each employee has responsibility for maintaining a safe and healthy
workplace for all employees by following safety and health rules and practices
and reporting accidents, injuries and unsafe equipment, practices or conditions.

     The Company will not tolerate violence and threatening behavior. Employees
should report to work in condition to perform their duties, free from the
influence of illegal drugs or alcohol. The Company will not tolerate the use of
illegal drugs in the workplace or on the Company's property. Please see the
Company's Employee Handbook for further guidance.

8.   RECORD-KEEPING

     The Company follows the accepted accounting rules and controls set forth by
the U.S. Securities and Exchange Commission and the Financial Accounting
Standards Board. The Company requires honest and accurate recording and
reporting of information in all circumstances, and without exception. The
Company requires that its certified public accountants have access to any and
all information necessary for them to conduct audits properly.

     Business expense accounts used by employees must be documented and recorded
accurately. If you are not sure whether a certain expense is legitimate, ask
your supervisor or the Controller. Rules and guidelines are available from the
Controller.

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     All of the Company's books, records, accounts and financial statements must
be maintained in reasonable detail, must appropriately reflect the Company's
transactions and must conform both to applicable legal requirements and to the
Company's system of internal controls. Unrecorded or "off the books" funds or
assets should not be maintained unless permitted by applicable law or regulation
and approved in writing by the Chief Financial Officer.

     Business records and communications often become public, and we should
avoid exaggeration, derogatory remarks, guesswork, or inappropriate
characterizations of people and companies that could be misunderstood. This
applies equally to e-mail, internal memos, and formal reports. Records should
always be retained or destroyed according to the Company's record retention
policies. In accordance with those policies, in the event of litigation or
governmental investigation, threatened or known, please consult with a
director-level or higher employee in the Law Department.

9.   CONFIDENTIALITY

     Employees must maintain the confidentiality of confidential information
entrusted to them by the Company or its customers, except when disclosure is
authorized by a director-level or higher employee in the Law Department, or
required by laws or regulations. Confidential information includes all
non-public information that might be of use to competitors, or harmful to the
Company or its customers, if disclosed. It also includes information that
suppliers and customers have entrusted to us. The obligation to preserve
confidential information continues even after employment ends.

10.  PROTECTION AND PROPER USE OF COMPANY ASSETS

     All employees should endeavor to protect the Company's assets and ensure
their efficient use. Theft, carelessness, and waste have a direct impact on the
Company's profitability. Any suspected incident of fraud or theft should be
immediately reported for investigation. Company equipment should not be used for
non-Company business, though incidental personal use may be permitted.

     The obligation of employees to protect the Company's assets includes its
proprietary information. Proprietary information includes intellectual property
such as trade secrets, patents, trademarks, and copyrights, as well as business,
marketing and service plans, engineering and manufacturing ideas, designs,
databases, records, salary information and any unpublished financial data and
reports. Unauthorized use or distribution of this information would violate
Company policy. It could also be illegal and result in civil or even criminal
penalties. Please see the Company's policies on IT usage and confidentiality
(copies of which are located in Cubist's Employee Handbook) for further
guidance.

11.  PAYMENTS TO GOVERNMENT PERSONNEL

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     The U.S. Foreign Corrupt Practices Act prohibits giving anything of value,
directly or indirectly, to officials of foreign governments or foreign political
candidates in order to obtain or retain business. It is strictly prohibited to
make payments to government officials of any country.

     In addition, the U.S. government has a number of laws and regulations
regarding business gratuities, which may be accepted by U.S. government
personnel, including, but not limited to, employees of Medicare, Medicaid, and
the Veterans Administration. The promise, offer or delivery to an official or
employee of the U.S. government of a gift, favor or other gratuity in violation
of these rules would not only violate Company policy but could also be a
criminal offense. State and local governments, as well as foreign governments,
may have similar rules.

     The Company does not contribute, directly or indirectly, to any political
campaign or party. Employees may not use company expense accounts to pay for any
personal political contributions or seek any other form of company
reimbursement. In addition, employees should not use company facilities or
company assets for the benefit of any party or candidate, including an employee
individually running for office. Employees are not prohibited from contributing
to properly established political action committees.

12.  MISREPRESENTATIONS AND FALSE STATEMENTS

     Employees must never make a deliberate misrepresentation concerning the
Company or its business operations. No employee shall create, or assist another
in creating, a false or misleading entry on the Company's books.

13.  RESPONDING TO GOVERNMENT REQUESTS

     Employees are expected to respond truthfully to Governmental inquiries. It
is the Company's policy to cooperate with all reasonable requests from
Governmental agencies concerning the Company's business operations.

14.  COMPLIANCE PROCEDURES

     We must all work to ensure prompt and consistent action against violations
of this Code. However, in some situations it may be difficult to know right from
wrong. Since we cannot anticipate every situation that will arise, it is
important that we have a way to approach a new question or problem. These are
the steps to keep in mind:

     -    MAKE SURE YOU HAVE ALL THE FACTS. In order to reach the right
          solutions, we must be as fully informed as possible.

     -    ASK YOURSELF. WHAT SPECIFICALLY AM I BEING ASKED TO DO? DOES IT SEEM
          UNETHICAL OR IMPROPER? This will enable you to focus on the specific
          question you are faced

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          with and the alternatives you have. Use your judgment and common
          sense; if something seems unethical or improper, it probably is.

     -    CLARIFY YOUR RESPONSIBILITY AND ROLE. In most situations, there is
          shared responsibility. Are your colleagues informed? It may help to
          get others involved and discuss the problem.

     -    DISCUSS THE PROBLEM WITH YOUR SUPERVISOR. This is the basic guidance
          for all situations. In many cases, your supervisor will be more
          knowledgeable about the question and will appreciate being brought
          into the decision-making process. Remember that it is your
          supervisor's responsibility to help you solve problems.

     -    SEEK HELP FROM COMPANY RESOURCES. In the rare case where it may not be
          appropriate to discuss an issue with your supervisor, or where you do
          not feel comfortable approaching your supervisor with your question,
          discuss it with any director-level or higher employee of Human
          Resources, any director-level or higher employee in the Law
          Department.

     -    YOU MAY REPORT VIOLATIONS IN CONFIDENCE AND WITHOUT FEAR OF
          RETALIATION. You may report violations or suspected violations of this
          Code by calling the Company's Corporate Responsibility Hotline at
          781-860-8600. All inquiries to the Corporate Responsibility Hotline
          will be handled confidentially to the extent reasonably possible. You
          may ANONYMOUSLY report violations or suspected violations of this
          Code, including, but not limited to, those: (i) relating to
          accounting, internal accounting controls, or auditing matters or (ii)
          by one or more of the Company's Executive Officers, by calling the
          Company's CONFIDENTIAL Corporate Responsibility Hotline at
          617-241-1456. The Company does not permit retaliation of any kind
          against employees for good faith reports of ethical violations.

     -    ALWAYS ASK FIRST, ACT LATER. If you are unsure of what to do in any
          situation, seek guidance before you act.

15.  HOW TO REPORT ANY ILLEGAL OR UNETHICAL BEHAVIOR

     Employees are encouraged to seek advice from: (i) their respective Vice
President, (ii) any director-level or higher employee in Human Resources, or
(iii) any director-level or higher employee in the Law Department about observed
illegal or unethical behavior and, when in doubt, about the best course of
action in a particular situation.

     YOU SHOULD REVIEW SECTION 13 IF YOU BELIEVE YOU HAVE OBSERVED ILLEGAL OR
UNETHICAL BEHAVIOR AND PROMPTLY REPORT SUCH BEHAVIOR TO: (i) YOUR VICE
PRESIDENT, (ii) ANY DIRECTOR-LEVEL OR HIGHER EMPLOYEE IN HUMAN RESOURCES, OR
(iii) ANY DIRECTOR-LEVEL OR HIGHER EMPLOYEE IN THE LAW DEPARTMENT. YOU MAY ALSO
REPORT SUCH BEHAVIOR TO THE COMPANY'S CORPORATE RESPONSIBILITY HOTLINE AT
781-860-8600. IF YOU WISH TO REPORT SUCH BEHAVIOR

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ANONYMOUSLY, YOU CAN CALL THE COMPANY'S CONFIDENTIAL CORPORATE RESPONSIBILITY
HOTLINE AT 617-241-1456. Employees are expected to cooperate in internal
investigations of misconduct.

16.  NO RETALIATION

     The Company will not retaliate in any manner, including, but not limited
to, discharging, demoting, suspending, threatening, harassing, or otherwise
discriminating against an employee who reports in good faith violations or
suspected violations of this Code, including, but not limited to, accounting
fraud or securities law violations.

17.  WAIVERS OF THE CODE OF BUSINESS CONDUCT AND ETHICS

     Any waiver of this Code for employees may be made only by the Board of
Directors. Any waiver of this Code for executive officers or directors may be
made only by the Board of Directors and will be promptly disclosed as required
by law or Nasdaq regulation.

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