"There's been five randomized control, placebo-controlled trials that do not show any benefit to hydroxychloroquine," Admiral Brett Giroir said.
Arizona Representative Ruben Gallego called the contract a "disgrace that must be fully investigated" on Tuesday.
"We've had more testing and had more results than any country anywhere in the world," President Trump said Monday.
Over 100 cases of the deadly virus, which has killed more than 3,000 people worldwide, have been confirmed in the U.S., according to Johns Hopkins University.
Several health programs are set to lose funds, including Medicare and Medicaid.
U.S. District Judge Dolly Gee has ordered the Trump administration to stop administering psychotropic drugs to children without parental consent or a court order.
The Trump administration is no longer disclosing how many children separated from their parents under its "zero tolerance" immigration policy are still in its care.
"This is a classic example of the adage 'No good deed goes unpunished,'" Health and Human Services Deputy Secretary Eric Hargan said.
The retired general tweeted about the now-vacant President's Council on Fitness, Sport and Nutrition, and that Ivanka Trump should "check it out."
Tom Price has resigned and will be succeeded by Don Wright, a disease prevention official.
Representative Tom Price of Georgia faces a second Senate committee on his nomination for health secretary.