But those who need it most, the severely mentally ill, can be hard to reach, especially if they are homeless or coming out of prison.
"This is not a population that is necessarily easy to enroll," Honberg said. "But if we can get people enrolled, the effects of the ACA could be huge."
Complementary and alternative medicine
Complementary and alternative medicine has tried for years to achieve mainstream acceptance. Now, the law may be helping it break through.
The section that could make a difference is Section 2706, the nondiscrimination clause. It states that insurers cannot discriminate against any health provider with a state-recognized license. They must pay for services such as a prevention visit or physical exam performed by any licensed person. These would include chiropractors, acupuncturists, and massage therapists. "These disciplines, and more importantly the patients interested in these disciplines, are honored and included in a way that they have never been before," said John Weeks, editor of the alternative medicine online site Integrator Blog. "What was outside is in; it's gigantic."
But some doubt it will happen. Erica Oberg, a naturopathic doctor at Bastyr University in San Diego, wonders whether insurers will comply with the law.
"The devil will be in the details, whether the implementation remains true to the intention," Oberg said. She suggests that patients call their insurers to ask how they plan to comply with Section 2706.
Either way, coverage will vary along with state licensing requirements and how states define their essential-benefits plan.
Once dismissed as a result of weak will, substance-use disorders will be on par with other chronic illnesses such as diabetes. Addiction care will be part of each marketplace plan as one of the essential benefits.
"There is no illness that is going to be more affected by the Affordable Care Act than substance-use disorders," said A. Thomas McLellan, CEO of the Treatment Research Institute in Philadelphia.
Until recently, substance abuse and addiction were considered criminal problems caused by bad parenting or lack of restraint, McLellan said.
Also, those treated tended to be the most affected, addicts receiving inpatient care. McLellan hopes the law will draw attention to those who are using substances at a "medically harmful" level, but who aren't classified as addicted.
The system is also expected to move toward prevention and treating substance use as a chronic condition. Insurance will now cover physician and clinic visits, family counseling, some anti-addiction medications, and smoking cessation.
The law has the biggest effect on current citizens. But it will have a similar impact on legal immigrants or legal permanent residents. Both face the individual mandate - they must buy insurance or pay a penalty.
But these groups are also eligible for tax credits and cost-sharing reductions to ease the burden of buying coverage. Medicaid may be another option, although in Pennsylvania and New Jersey, most adults must be legal residents for five years to be eligible. And for those without legal status?
"For the undocumented, the law essentially provides no help at all," said Drexel University law professor Robert Field. "They are where they were before the law came into effect."
These individuals will not be allowed to buy insurance in the marketplace, nor will they be eligible for tax credits. They must rely on public health centers and ERs or try to find insurance outside the new exchanges.
"Many immigrant families are mixed-status families, so it's tricky," said Jenny Rejeske, a health-policy analyst at the National Immigration Law Center. According to the Pew Research Center, 8.8 million people live in mixed-status families.
Once largely confined to public programs and largely rejected by private insurers, disabled Americans will have unprecedented options in the marketplace.
"The law gets rid of preexisting condition exclusions, so people with disabilities will have access to private health-care coverage," said Henry Claypool, executive vice president of the American Association of People with Disabilities. "It's a very significant accomplishment."
Before, the only guaranteed health insurance came from public programs such as Medicaid, but that also meant certain income and asset restrictions applied.
"You are not permitted to work at any significant level, because once you do, you compromise your eligibility for Medicaid," Claypool said. "It has been a real disincentive for people with disabilities to work."
He believes the law will help disabled people achieve greater economic self-sufficiency.
It also provides and expands financial incentives to states for their Medicaid programs to better serve those with disabilities in their homes and communities. A disabled person might get daily assistance from an aide to avoid going into a nursing home.
The law will give small businesses more options, but some larger companies may be getting the worst deal.
The law creates a division between what it considers a small business and a large employer, drawing the line at 50 full-time, or full-time equivalent, employees. Even when a business has 30 full-time employees and 100 part-timers, the total number of hours would likely put it in the large-employer group.
"The biggest losers of the Affordable Care Act will be some companies with more than 50 employees that have to pay coverage, but are not eligible for federal subsidies," said Drexel's Field. "It's a glitch in the law that I hope Congress is able to take care of."
Larger firms will be subject to the "pay or play" penalty starting in 2015, with employers required to provide health insurance to full-time employees and eligible dependents or face a penalty. But 94 percent of firms with 50 to 199 employees already offer coverage, so this change won't affect most businesses.
Those with fewer than 50 employees will have access to the Small Business Health Options Program, or SHOP marketplace, a new way to find insurance packages for employees. But because the "pay or play" rule doesn't apply to them, they also can forgo coverage and have employees use the marketplace to find their plans.
"It really does open it up for these small businesses to rethink and have options," said Eric Pochas, director of client services for the consulting firm Vantagen. "They were once handcuffed with what they could do."
Added Mark Duggan, a business economist at the Wharton School: "The current system pre-ACA worked terribly for small companies." He stressed that workers in small firms are three times more likely to be uninsured than their counterparts in large firms.
"It was so hard for them to get health insurance," Duggan said, "and they ended up getting prices that are 20 percent higher than big companies."
This story was produced in partnership with Kaiser Health News, an editorially independent program of the Henry J. Kaiser Family Foundation, a nonprofit, nonpartisan health-policy research and communication organization not affiliated with Kaiser Permanente.