(CNN) They're not slumped over in alleyways with used needles by their sides. Their dignity, at least from outside appearances, remains intact. They haven't lost everything while chasing an insatiable high.

They are functioning heroin addicts -- people who hold down jobs, pay the bills and fool their families.

For some, addiction is genetic; they're wired this way. For others, chronic pain and lack of legal opioids landed them here. Or experimentation got them hooked and changed everything.

What addicts have in common, according to experts, is a disease that has more to do with their brains than the substances they use. About 85% of people can take a pain pill, for example, and never crave it again.

This is a story about the others, those traveling the dangerous road of functional addiction. What works for them now, experts explain, can easily and lethally be derailed.

Hanging in the balance are people you may never imagine: peers, co-workers and neighbors. Loved ones, bosses and teachers. Respected members of your community who, for the benefit of everyone's understanding, want to be heard.

After CNN gave voice last fall to addicts on skid row , the sorts we think of when we picture "heroin addict," I set out to tell this overlooked part of the heroin story.

Being a functioning addict hinges on heroin use staying hush-hush, so we agreed to change the names of those willing to open up.

'All smiles and happiness at work'

Loving and successful parents, good schools, a great upbringing in the Midwest: Todd can't point to anything that drove him to drugs. He was a typical suburban high school student who dabbled in weed. Then, at 15, he popped a Percocet his mother left lying around while she was recovering from surgery.

"The feeling in my head was, 'I want to feel like this for the rest of my life,' " Todd says. "It was the perfect drug for me."

The 11 years since have been a dance with opioid addiction, even as he graduated from college and embarked on a successful career in corporate management. Now 26, he has gone stretches where he's been sober, but the pull is strong and keeps yanking him back.

He's done heroin for periods of time and says it's "fantastic," but shooting up isn't his style. His preference, assuming he can find them, is to buy more expensive opioids. For a long time, OxyContin was his drug of choice; now he prefers Opana and, if he can't get that, Subutex.

He makes good money, which means he can afford his $350- to $600-a-week habit.

He's figured out how much to take so he doesn't feel the pains of withdrawal, which is now his goal -- rather than getting a full-on high. His sweet spot: 60 milligrams of Opana.

"I don't know how to describe withdrawal. It's like the worst flu you've ever had in your life -- and then multiply that by 1,000," he says. "There's a scraping inside your brain. You're willing to do anything to feel better."

To avoid that hell, Todd often lives a lie. He's "all smiles and happiness at work," he says, and he spins tales to guard his secret. He might say he's in one city when he's really in another. That quick trip he says he's taking to McDonald's could be to meet his dealer at Burger King. When he's used heroin, he's explained the bruises on his arm by telling people he has diabetes or an infectious disease. He once told a pharmacist he was a science teacher in need of syringes for experiments. He's invented the deaths of family members to get days off.

But death is very much a reality in his life.

His last serious girlfriend also used drugs and died from an overdose. Over the past six years, he's lost seven people he cares about to addiction.

He'd like to find love, build a relationship and have a family but says, "It would be dishonest, and I never want to hurt anybody. That's the biggest problem."

He knows that he has a lot to live for, but he often forgets that and struggles to imagine a future. And because he can't stray far from his dealer, a dream he does have remains on hold indefinitely.

"I've always wanted to see the world," he says. "I've never been outside the country because I can't leave. I'm f***ing chained where I'm at. It's a f***ing prison."

The sign of an addict

The sensation Todd had the first time he popped a Percocet, that feeling he wanted to hold onto for the rest of his life, was the giveaway. He, like 10% or 15% of people, has the disease of addiction, explains Dr. Stuart Gitlow, past president of the American Society of Addiction Medicine

What offers no special high for most people or may even make them feel queasy became Todd's aspiration. And part of the problem, says Gitlow, is that "you don't know in advance what person you're going to be."

Todd may be functioning now, but Gitlow warns that tolerances and doses often change. As an addictive disease progresses, it is also influenced by life events and stressors. What happens if Todd loses his job someday or can't afford his preferred pills?

"They all start out functioning," he says. "The bulk of people taking heroin are probably functioning. It's only in the end stage that they're nodding off in an alley and have a pretty good shot of dying."

What Todd needs, Gitlow says, is help from a doctor who is certified in addiction medicine and can treat his disease. The vast majority, or 80%, of those who seek appropriate treatment and adhere to their treatment recommendations do well, he says.

Not a unique story

It didn't start with a pill for Lisa. Her first addiction took hold at 12, when she began cutting herself.

Carving into her flesh released dopamine in her brain, giving her a high, she says. The first time she did it, she never anticipated a rush. She was overwhelmed emotionally and simply acting out. But cutting became her way to self-medicate because it offered her solace, easing the emotional pain of living in a household full of screaming.

Now, at 23, Lisa opts for heroin. And because of it and other opioids she's used, "I hurt myself a lot less."

The difference now is that she, like Todd, no longer seeks a high. When she shoots up each morning, she insists, "I just do enough to stay well" through the day and not feel physical pain.

She works hard, always has. She excelled in her college-prep private school, where she was dubbed "gifted and talented," she says. She takes her job as a store manager seriously and enjoys a supportive marriage. No one at work knows that her day begins with a call to her dealer. If she has track marks, a simple long-sleeved shirt hides the evidence.

How she found heroin, she says, is not unique.

Long plagued by tendonitis in her knees and two herniated discs in her back, Lisa tried everything. Steroid injections gave her migraines, and her stomach couldn't handle anti-inflammatories. Physical and aquatic therapies offered little relief, as did deep-tissue massage. Finally, four years ago, a physician wrote out a prescription for pain pills.

She found comfort in those legal opioids. But then came the crackdown on opioid prescriptions, she says, effectively ending her lawful pain management.

Once her pills ran out, she turned to buying them on the street. They were hard to find, though, and the cost became prohibitive. An old friend, a heroin user, suggested that she give his drug a try.

"I can't find pills, I'm in pain, and it's really cheap," she remembers telling herself. "What happened to me is what happened to thousands and thousands of people."

Where she lives in Texas, near the Mexican border, the price of heroin can't be beat. One pill might cost her $50, but she can get half a gram of heroin, which is far more potent, for $20. The same product, she says, would cost up to five times as much in other parts of the country.

"If I moved somewhere where it was $100," she says, "I'd quit."

Her husband doesn't do drugs. He barely drinks. And although he'd prefer she kick the habit altogether, he's committed to being by her side -- so much that he keeps Narcan, the overdose antidote drug, in their home and has watched training videos to learn how to administer it in case she overdoses.

"He loves me enough that he's willing to stay with me," Lisa says. "That's a key component to keeping me from going off the deep end."

Lisa says a small handful of friends know that she uses heroin. Everyone else, her family included, believes she's hooked on "just pills." It's easier that way. Pills and other vices don't come with the same sort of judgment.

"People drink, and we think nothing of it. You do heroin, and you're the scum of the earth," she says. "People will cut you out of their lives."

Everybody's problem

Heroin users weren't always "the scum of the earth." In the late 19th century, it was a trademark name for an over-the-counter drug made by Bayer.

Today, there are politics behind which drugs are demonized and which aren't, and much of that is rooted in racism, says Dr. Michael Miller, who preceded Gitlow as president of the American Society of Addiction Medicine.

White socialites snorting cocaine in an Aspen ski lodge are forgiven, while inner-city blacks smoking crack -- just another form of cocaine -- are vilified and locked away, Miller explains. Heroin was romanticized when musicians used it, he says, but after black kids in coastal cities got hold of it, the perception changed and stuck.

Now, with the explosion of the opioid epidemic and the emergence of heroin as a less expensive alternative, it's become everybody's problem -- white or black, rich or poor, on the coasts or in middle America, no matter whether you live in a city, suburb or rural community.

That's how Lisa got roped in and learned to keep a secret.

She admits that the management of her addiction hinges in large part on her husband being by her side. But what if he leaves? What if life tosses her another kind of doozy? How much heroin would she need to ease her pain then?

"She has no coping skills. She's right at the edge," Gitlow says. "What if her dealer gets arrested and her new dealer mixes in fentanyl? Boom. She's dead."

'Like downing a beer'

Not everyone I spoke to considers themselves addicts. Enter Matthew.

For as long as Matthew can remember, he's battled anxiety and depression. Beyond prescriptions like Xanax or Valium, he began self-medicating at 19 with marijuana and LSD, he says.

An arrest for possession of pot and LSD with intent to distribute landed him on probation. Facing regular drug tests that would detect cannabis, he turned to harder drugs that wouldn't stay in his urine as long. That's how Matthew, 28, first tried oxycodone.

Later, a doctor would prescribe opioids for chronic stomach pain, a condition he's had for six years.

It's the sort of pain, he says, that used to leave him racing to bathrooms so frequently, he couldn't keep a job. Multiple GI doctors have tried to help him. Only prescribed opioids and marijuana have offered relief.

Raised in the Eastern US, he now lives in rural Northern California and works as a consultant in the cannabis industry. He doesn't hide his marijuana use or his dependence on pain medications.

It's the powdered heroin he purchases on the dark net, the stuff he snorts in the bathroom a few times a day, that he keeps to himself. He says he uses it only when his prescriptions or insurance coverage lapse.

He's never used heroin intravenously. Having gone back and forth between pharmaceuticals and illegal supplies, he says he's able to use a milligram scale to carefully measure how much of the powder to take.

"It's similar to a dose of Percocet." he says. "The effect would be like downing a beer or a cocktail."

He doesn't use a lot and says he snorts only about $5 of heroin a day. He's stopped in spurts and has written down pro and con lists to see whether he can move on. The pros keep winning out.

"I just don't find sober me is the best me," he says.

Having a secret can be isolating, he says, but otherwise, heroin has not hindered his life. Rather, Matthew says, "It's changed my life for the better."

Not only does it help with the pain, he says, it constipates him, allowing him to ditch the bathroom and get out of the house.

"I'm dependent," he says. "But I wouldn't necessarily call myself an addict."

The crippling truth

Matthew is kidding himself, experts say.

"Denial is a crippling component of addictive disease," Gitlow said. "Here we have a well-documented illustration of that deadly component."

Starting at 19, the signs were there when Matthew turned to drugs rather than "conventional coping mechanisms," Gitlow explains. Someone without the addictive disease might have tried those drugs for temporary relief but then realized they weren't worth the long-term risk.

Matthew's belief that he doesn't have a problem, Gitlow says, is no different from a man with hypertension or diabetes pretending there's nothing wrong with him.

Plus, using heroin and other opioids changes brain chemistry, says Siobhan Morse, director of clinical services for the Foundations Recovery Network.

The natural way a body manages pain or stress, Morse says, is by producing endorphins.

"If you're giving it the artificial substance," she explains, the brain thinks it doesn't have to make the real thing. "So when you take away the artificial substance, everything is so painful."

And for people like Matthew who have coexisting mental health issues such as anxiety or depression, self-medication with opioids can make those matters worse, Morse adds. She describes the combination as a "moving target."

Eventually, she and other experts say, Matthew's drug use will catch up with him.

"I've never met anyone who's indefinitely held it down being a heroin addict," Morse says.

The fall of 'Superwoman'

Rebecca has been using for more than three decades -- longer than Matthew, Todd and Lisa combined. She is surprised to still be alive.

She grew up in an upper-middle-class household in a tony suburb in the South where she was raised more by the housekeeper than her parents. Her mother was checked out; her father had mistresses and often traveled.

"I didn't have any boundaries," says Rebecca, 59. "I could do whatever I wanted, which was a recipe for disaster."

Starting at 12, she tried every narcotic she could find. At 15, the man who was her drug dealer and boyfriend introduced her to heroin.

"I was in love," she says of the drug. "It became the love of my life."

One day, she was sleeping on the couch in her family's home when an older sister pinned her down, rolled up one of her sleeves and called out her track marks.

"Mom didn't bat an eye," Rebecca remembers. Instead, she shrugged it off, saying, "Jewish people aren't addicts."

Her father, when he was around, was more a friend than a parent. He partied with Rebecca and gave her Quaaludes, she says.

Rebecca eventually married the drug dealer-boyfriend, and they had a daughter. But the marriage was short-lived.

Divorced and 24, Rebecca went into treatment after her daughter turned 3. Rebecca knew that she was unfit to be a parent and feared she'd lose her daughter forever. It was the first of some 20 times she'd check into a treatment facility for help.

Along the way, she re-married; husband No. 2 died of a heroin overdose.

Rebecca met her third husband in treatment and stayed sober for eight years. They had two more children and a comfortable lifestyle, enjoying the sort of privileges she knew growing up. But when this marriage fell apart, so did she.

"That was when I started to spiral down," Rebecca says. "As soon as I started using, it was immediate. ... It was like I never stopped using."

Even as Rebecca returned to heroin, spending $100 or more a day, she built a career in corporate travel, working for big-name companies.

"As long as I didn't run out [of heroin] and get sick, I was like Superwoman," she says of her job performance. "If I had come in and said I was a heroin addict, people would have laughed."

Years of use caught up with her. Lunchtime runs to see her dealer grew longer and became lies about flat tires or broken-down cars. She bounced around between five or six companies, taking extended leaves to go into treatment or try to detox at home. She kept overdosing. A $30,000 mistake at work got her fired.

"People kept saying, 'You're going to die,' " Rebecca says. "The problem with me wasn't that I was going to die, it's that I was going to live."

Her kids were mostly raised by other family members and knew her at her worst. They'd see her after overdoses and visit her in the "nasty places" she called home. "It was just awful," says Rebecca, who's still working to repair the relationships she frayed.

Today, Rebecca is three years sober.

The last time she entered treatment, she says, "something clicked, and I remember thinking, 'I can't do this anymore.' "

She was "sick and tired of being sick and tired," she says. "I didn't have it in me anymore to keep doing what it took to stay high."

Follow CNN Health on Facebook and Twitter See the latest news and share your comments with CNN Health on Facebook and Twitter.

Rebecca is not the only member of her family who's struggled. One relative is an alcoholic, another is also a heroin addict, and a third -- who won't touch heroin because of Rebecca -- is hooked on pain pills.

"It's in the genes," Rebecca says. "No doubt."

She has seven grandchildren and is determined to be a better grandmother than she was a parent. She lives with a friend in an apartment and works part time for a sober living community.

"If there's any regret, it's that I've missed decades," Rebecca says. "I just thought I wasn't going to live, so I never worried about getting old."

She is fighting to make the rest of her life matter, all the while knowing -- based on decades of experience -- how easily she could slip again.

One lapse, one moment of weakness or overconfidence that she can handle it, and everything Rebecca is building up could come crashing down and, quite possibly, bury her.