The Drug Enforcement Agency wants the reclassification and an FDA panel voted earlier in the year to reclassify hyrdocodone, but the FDA has yet to grant final approval for the shift.
"(I'm) totally, absolutely frustrated, trying to figure out a way for the FDA to try and reschedule hydrocodone," Manchin said.
He believes an investigation could help precipitate a change, but he also wants to see if the FDA or the pharmaceutical companies involved did anything illegal.
He sent a letter to FDA Commissioner Margaret Hamburg asking her to provide information about the panel's meetings, companies who paid to attend, panel recommendations and more.
"These press reports raise troubling questions about the FDA's delay in issuing a recommendation regarding this petition," Manchin wrote in the letter.
"I truly hope that the FDA is not allowing their relationship with the pharmaceutical industry to influence their duty to protect the American public."
Manchin said he expected Hamburg, members of the panel, officials from the companies and others to be subpoenaed for the hearing. The Washington Post story and Manchin's letter do not specifically name any pharmaceutical companies.
The partial shutdown of the federal government should not affect the hearing or investigation, Manchin said.
The senator bemoaned the shutdown, calling it "craziness" that needs to end. He said there needs to be a negotiation as to how to fund the government, and scolded Republicans for not accepting a previous deal from Democrats on the debt ceiling.
Manchin did not say if he would support a Democrat-backed measure to raise the country's borrowing limit without attaching any other amendments. He said he doesn't like the idea of attaching social policies to such a bill.
"But sooner or later we're going to have to be serious about fixing the debt of the nation," Manchin said.
Experts expect the county will reach the debt ceiling Oct. 17.Contact writer Dave Boucher at 304-348-4843 or david.bouc...@dailymail.com. Follow him at www.twitter.com/Dave_Boucher1.