U.S. stocks opened lower on Thursday after U.S. President Donald Trump unveiled a massive overhaul to the tax system.

The Trump administration and U.S. Congress Republicans on Wednesday released a unified framework for tax code reform, which will cut tax rates for businesses and individuals while lacks details on how to consolidate fiscal position in face of big tax cuts.

Analysts said the excitement that lifted equities on Wednesday was replaced by questions on how the plan will be put in place.

On the economic front, U.S. real gross domestic product (GDP) increased at an annual rate of 3.1 percent in the second quarter of 2017, on par with market consensus, according to estimate released by the Commerce Department on Thursday. In the first quarter, real GDP increased 1.2 percent.

In the week ending Sept. 23, the advance figure for seasonally adjusted initial claims was 272,000, an increase of 12,000 from the previous week's revised level, the U.S. Labor Department announced on Thursday.

The four-week moving average was 277,750, an increase of 9,000 from the previous week's unrevised average of 268,750. This is the highest level for this average since Feb. 6, 2016 when it was 277,750.

Shortly after the opening bell, the Dow Jones Industrial Average fell 30.50 points, or 0.14 percent, to 22,310.21. The S&P 500 dipped 1.62 points, or 0.06 percent, to 2,505.42. The Nasdaq Composite Index decreased 12.29 points, or 0.19 percent, to 6,440.97.