President-elect Donald Trump promised to take control of the heroin and opioid epidemic that has taken the U.S. by storm, but some experts are concerned how he can accomplish such a mission if Obamacare is repealed.

Senate Republicans made a major move Thursday when they approved a budget blueprint that would make their agenda to dismantle the Affordable Care Act (ACA) more achievable. But repealing the law would result in more than 20 million people losing health care coverage, many of whom are recipients struggling with mental health and addiction, who were able to gain health coverage through ACA’s Medicaid expansion.

About 30 percent of people covered by ACA struggle with addiction to substances like opioids and alcohol or suffer from a mental disorder like schizophrenia, according to the federal Substance Abuse and Mental Health Administration. While stopping the flow of illegal drugs as Trump proposed during his campaign would be decidedly helpful in preventing more people from having access to drugs, lawmakers believe repealing Obamacare would have an immediate adverse effect on people who are currently using their coverage to get treatment for their addiction.

“He pledged to take on this crisis, not immediately make matters much worse,” Sen. Jeanne Shaheen, D-N.H., said in a statement to USA Today. “Repealing the Affordable Care Act without a replacement is highly reckless and will come at a high cost for people struggling with substance use disorders.

In New Hampshire, which has the highest synthetic opioid death rate in the nation, more nearly 120,000 people would lose health coverage if the ACA was repealed, 48,000 of which Shaheen said filed Medicaid claims for substance use disorder in 2015.

In a Wednesday report in The Hill, two researchers from Harvard Medical School and New York University said repealing the ACA and its behavioral health provisions would have “stark effects” on people suffering from behavioral illnesses and drug addiction. The report said roughly 2.8 million Americans have a substance use disorder, 222,000 of whom are battling an opioid disorder and would lose some or all of their coverage if the ACA is repealed.

Heroin and opioid overdose killed more than 33,000 people in the U.S. in 2015, which the Centers for Disease Control said was the highest number of fatal overdoses than any year on record.