UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

March 27, 2012 (March 26, 2012)

Date of Report (date of earliest event reported)

NEUROGESX, INC.

(Exact name of Registrant as specified in its charter)

2215 Bridgepointe Parkway, Suite 200, San Mateo, California 94404

(Address of principal executive offices)

(650) 358-3300

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

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 (see General Instruction A.2. below):

On March 26, 2012, NeurogesX, Inc. (the “Company”) entered into an amendment (the “Amendment”) of a warrant originally issued on August 5, 2011 (the “Warrant”) to Hercules Technology Growth Capital, Inc. (“Hercules”) in connection with the entry of the Company into a Loan and Security Agreement with Hercules. Under the terms of the Amendment, changes were made to Section 9(h) of the Warrant to require the Company to maintain the listing of its common stock on the Nasdaq Global Market, Nasdaq Capital Market, OTCBB, OTCQB or OTCQX instead of the original terms of such section which required the Company to maintain such listing only on the NASDAQ Global Market. Additionally, the number of shares of Company common stock underlying the Warrant was increased from 791,667 to 1,950,000 and the exercise price per share of common stock was decreased from $1.80 to $0.50. No other consideration was provided by either party in connection with entry into the Amendment.

The Amendment was entered into pursuant to the exemption from registration provided by Section 4(2) of the Securities Act of 1933, as amended, and by Regulation D promulgated thereunder.

The foregoing is not a complete summary of the terms of the Amendment or the Warrant described in this Item 1.01, and reference is made to the complete text of the Amendment attached hereto as Exhibit 4.1 and the Warrant attached as Exhibit 4.1 to the Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission on August 9, 2011 (the “Original 8-K”). A description of other terms of the Warrant contained in Item 1.01 of the Original 8-K is also hereby incorporated by reference into this Item 1.01.

The information set forth in Item 1.01 of this Current Report on Form 8-K is incorporated by reference into this Item 3.02.

The information set forth in Item 1.01 of this Current Report on Form 8-K is incorporated by reference into this Item 3.03.

The following Exhibit is filed as part of this Current Report on Form 8-K:

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.

EXHIBIT LIST