13G Filing: Perceptive Advisors and Global Blood Therapeutics Inc (GBT)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Global Blood
Therapeutics, Inc.

(Name of Issuer)

Common Stock, $.001 par value

(Title of Class of Securities)

37890U 10 8

(CUSIP
Number)

December 14, 2017

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to
designate the rule pursuant to which this Schedule is filed:

☐ Rule 13d-1(b)

☒ Rule 13d-1(c)

☐
Rule 13d-1(d)

The information required in the remainder of this cover page shall not be
deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).

CUSIP No. 37890U 10 8

CUSIP No. 37890U 10 8

CUSIP No. 37890U 10 8

Global Blood Therapeutics, Inc. (the Issuer)

171 Oyster Point
Boulevard, Suite 300

South San Francisco, CA 94080

The names of the persons filing this report
(collectively, the Reporting Persons) are:

Perceptive Advisors LLC (Perceptive Advisors)

Joseph Edelman (Mr. Edelman)

Perceptive Life Sciences Master Fund, Ltd. (the Master Fund)

The address of the
principal business office of each of the Reporting Persons is:

51 Astor Place, 10th Floor

New York, NY 10003

Perceptive Advisors is a Delaware limited liability company

Mr. Edelman is a United States citizen

The Master Fund is a Cayman Islands corporation

Common Stock, $.001 par value
(Common Stock)

37890U 10 8

Not applicable.

The information required by this item with respect to each Reporting
Person is set forth in Rows 5 through 9 and 11 of the cover page to this Schedule 13G. The ownership percentages reported are based on 46,007,393 outstanding shares of Common Stock, as reported in the Issuers prospectus filed on December 19,
2017.

The Master Fund directly holds 4,889,066 shares of Common Stock. Perceptive Advisors serves as
the investment manager to the Master Fund and may be deemed to beneficially own the securities directly held by the Master Fund. Mr. Edelman is the managing member of Perceptive Advisors and may be deemed to beneficially own the securities
directly held by the Master Fund.

If this statement is being filed
to report the fact that as of the date hereof the Reporting Persons have ceased to be the beneficial owner of more than five percent of the class of securities, check the following ☐.

Not
applicable.

Not applicable.

Not applicable.

Not applicable.

By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as
a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of its knowledge and belief, each of the undersigned certifies that the information set forth in this
statement is true, complete and correct.

EXHIBIT 1

AGREEMENT

The persons below hereby agree that
the Schedule 13G to which this agreement is attached as an exhibit, as well as all future amendments to such Schedule 13G, shall be filed on behalf of each of them. This agreement is intended to satisfy the requirements of Rule 13d-1(k)(1)(iii) under the Securities Exchange Act of 1934.