By Toni Clarke

(Reuters) - The U.S. House of Representatives is expected to pass a $6.3 billion piece of legislation on Wednesday designed to spur medical innovation, speed access to new drugs, expand mental health treatment, and combat opioid abuse.

The bill, known as the 21st Century Cures Act, provides $4.8 billion to the National Institutes of Health (NIH) over 10 years to support brain, cancer and precision medicine research. It also provides $500 million to the Food and Drug Administration to approve drugs and devices more quickly.

President-elect Donald Trump has promised to cut "red tape" at the FDA. He has not commented specifically on 21st Century Cures. The U.S. Senate is expected to vote on the bill next week. It is expected to pass, though possibly not before some additional changes are made. It would then go to President Barack Obama for signature.

The bill calls for $1 billion over two years to treat and prevent opioid abuse, including improving prescription drug monitoring programs, training for health care providers, and expanding access to opioid treatment programs.

Critics of the bill, including Senator Elizabeth Warren of Massachusetts, a Democrat, said it contains too many give-aways to the pharmaceutical industry and will allow companies to push treatments with limited proof of efficacy.

Speaking on the Senate floor on Monday, Warren said she could not vote for the bill despite its many positive elements and would not be a "lackey" for the drug industry.

Warren, along with Republican Senator Charles Grassley of Iowa, also objects to a provision that would allow companies to hide payments to doctors under the auspices of continuing medical education. Grassley co-authored the Sunshine Act which led to the creation of a database listing drug and device company payments to doctors.

"A lot of earlier payments to doctors were under the umbrella of Continuing Medical Education," Grassley said in a statement on Monday. "We shouldn't create a loophole that would let drug and medical device companies mask their payments to doctors under a payment category that's too broad and could gut the spirit and the letter of the Sunshine Act."

The bill would add an additional reporting exemption for physicians who receive indirect payments for speaking fees.

Patients groups hailed the bill, saying it would bring patient voices to the center of the drug approval process.

"This is a patient-centered bill," said Ellen Sigal, chair and founder of Friends of Cancer Research, a patient advocacy organization. "It fosters innovation and doesn't lower safety standards."

(Reporting by Toni Clarke in Washington; editing by Diane Craft)