<Page>
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) September 20, 2002
-------------------------------
TRIANGLE PHARMACEUTICALS, INC.
- --------------------------------------------------------------------------------
(Exact name of registrant as specified in its charter)
DELAWARE 000-21589 56-1930728
- --------------------------------------------------------------------------------
(State or other jurisdiction (Commission (IRS Employer
of incorporation) File Number) Identification No.)
4 University Place, 4611 University Drive, Durham, North Carolina 27707
- --------------------------------------------------------------------------------
(Address of principal executive offices) (Zip Code)
Registrant's telephone number, including area code (919) 493-5980
-----------------------------
- --------------------------------------------------------------------------------
(Former name or former address, if changed since last report)
<Page>
ITEM 5. OTHER EVENTS.
On September 20, 2002, Triangle Pharmaceuticals entered into an Amended
and Restated Employment Agreement with Chris Rallis, a copy of which is attached
hereto as Exhibit 10.1.
On September 20, 2002, the stockholders of Triangle Pharmaceuticals
approved the Third Amendment to the Triangle Pharmaceuticals, Inc. 1996
Incentive Plan. A copy of the amendment is attached hereto as Exhibit 10.2.
ITEM 7. FINANCIAL STATEMENTS, PRO FORMA FINANCIAL INFORMATION AND
EXHIBITS.
(c) Exhibits. The following documents are filed as exhibits to this
Report:
10.1 Amended and Restated Employment Agreement dated September 20,
2002 between Triangle Pharmaceuticals, Inc. and Chris A. Rallis.
10.2 Third Amendment to Triangle Pharmaceuticals 1996 Incentive Plan.
SIGNATURES
Pursuant to the requirements of the Securities Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.
Triangle Pharmaceuticals, Inc.
--------------------------------------------------
(Registrant)
September 23, 2002 /s/ Robert F. Amundsen, Jr.
- ---------------------------- --------------------------------------------------
Date (Signature)
Name: Robert F. Amundsen, Jr.
Title: Executive Vice President and
Chief Financial Officer
2