MANCHESTER, N.H. — Chad Diaz began using heroin when he was 12. Now 36 and newly covered by Medicaid under the Affordable Care Act, he is on Suboxone, a substitute opioid that eases withdrawal symptoms and cravings, and he is slowly pulling himself together.
"This is the best my life has gone in many, many years," Mr. Diaz, a big man wearing camouflage, said as he sat in a community health center here.
If Congress and President Trump succeed in dismantling the Affordable Care Act, he will have no insurance to pay for his medication or counseling, and he fears he will slide back to heroin.
"If this gets taken from me, it's right back to Square 1," he said. "And that's not a good place. I'm scary when I'm using. I don't care who I hurt."
As the debate over the fate of the health law intensifies, proponents have focused on the lifesaving care it has brought to people with cancer, diabetes and other physical illnesses. But the law has also had a profound, though perhaps less heralded, effect on mental health and addiction treatment, vastly expanding access to those services by designating them as "essential benefits" that must be covered through the A.C.A. marketplaces and expanded Medicaid.