NEW YORK/WASHINGTON (Reuters) - U.S. President Donald Trump on Monday took aim at Pfizer Inc and other U.S. drugmakers after they raised prices on some of their medicines on July 1, saying his administration would act in response.

U.S. President Donald Trump gestures during a Make America Great Again rally in Great Falls, Montana, U.S., July 5, 2018. REUTERS/Joshua Roberts

“Pfizer & others should be ashamed that they have raised drug prices for no reason.” Trump wrote in a post on Twitter on Monday. “We will respond!”

Health and Human Services Secretary Alex Azar followed up with his own tweet saying that drugmakers who have raised prices have created a tipping point in U.S. drug pricing policy.

“Change is coming to drug pricing, whether painful or not for pharmaceutical companies,” Azar wrote.

Neither Trump nor Azar detailed what policy changes would be implemented to decrease prices.

Trump had said in May that some drug companies would soon announce “voluntary, massive” cuts in prices, but none have materialized yet. During his presidential campaign, he promised lower U.S. drug costs.

Pfizer raised list prices on around 40 medicines earlier this month. Those include Viagra, cholesterol drug Lipitor and arthritis treatment Xeljanz, according to Wells Fargo. List prices do not include rebates and discounts drugmakers may offer.

“The list price remains unchanged for the majority of our medicines. Our portfolio includes more than 400 medicines and vaccines. We are modifying prices for approximately 10 percent of these, including some instances where we’re decreasing the price,” Pfizer spokeswoman Sally Beatty told Reuters.

Pfizer’s stock fell after Trump’s tweet - they closed up 5 cents at $37.16, but had been trading at $37.44 just before the tweet.

Pfizer was not the only major drug company to raise prices after Trump suggested they would voluntarily slash prices. Israeli generic drugmaker Teva Pharmaceutical Industries Ltd hiked prices on 14 drugs in June and Roche Holding’s Genentech division raised prices on a number of its drugs on July 1, according to Wells Fargo.

Teva and Roche could not be immediately reached for comment.