“I’m really good at selling drugs — like really good,” Ragan said right before she climbed up the stairs to do a four-figure deal with one of her Manhattan clients.

She wore blue eyeshadow, an oversized sweatshirt and Birkenstocks, still looking like the smart undergrad who just two years earlier took a math degree at one of the best colleges in the country. MDMA, the main ingredient in ecstasy, and thousands of dollars of cash were stashed in a cloth backpack hanging over her shoulder.

Ragan was slinging merchandise for one of the biggest MDMA-dealing rings in the Northeast, grossing up to $45,000 a month for a couple of hours worth of work a day. Together she and her bosses, Chad, a floppy-haired rich kid from Texas who worked as a distributor, and Nick, the “connect” to British Columbia, run a $4 million-a-year operation.

Ecstasy is a party drug, popular especially among fans of electronic dance music. Ragan and her team specialize in a type called “Molly” that comes in a white powder form encased in gel caps. It triggers a high by releasing serotonin, giving the user a feeling of happiness or serenity for about three to six hours. Beats become richer, glo-sticks glow brighter. Everyone is your friend.

It also causes an hour or so low-mood period after that, called the comedown, that can include depression and paranoia. Medical studies show that ecstasy can cause long-term brain damage.

Labs hidden deep in the wilderness of Canada, along its western and eastern coasts, manufacture the bulk of the world’s ecstasy supply and almost all of the supply to the US.

A popular drug in the 1990s, ecstasy has seen a resurgence in the past few years. MDMA seizures along the Canadian border jumped from about 500 pounds in 2006 to more than a 1,000 pounds in 2010, according to the Justice Department. Seizures last year in New York surpassed those in the late 1990s. And studies show a surge in MDMA use among those 12 or older since 2007, with the largest increase being among 18- to 25-year-olds.

Though drugs like cocaine arrive in greater supply, ecstasy has a broader reach. Because of corruptions of the recipe, including chemicals called “bath salts,” meanwhile, ecstasy has become more dangerous.

But that hasn’t stopped young people like Ragan from getting into the business, lured by widespread demand. It’s money, she says, for almost nothing.

In exchange for an extraordinary level of access into their business, The Post changed their names and a few potentially identifying details. Everything else is the straight dope.

Ragan’s first client of the day is Jerod, a NYU student with cute green eyes and freckles, who lives in a small two bedroom in lower Manhattan.

She sat down in his room — a space that barely fit one twin-sized bed and a dresser — and he pulled out a nice wad of cash. He’d purchased a sizeable quantity of drugs in recent weeks and owed Chad $1,050.

“How can he wait so long for that much money?” asked Jerod. Ragan ignored the question. The answer seemed obvious enough: Chad, her boss, makes so much green he doesn’t care.

Ragan’s phone rang. It was Nick, Chad’s business partner. Ragan stepped into the living room and talked money with him, quietly negotiating the repayment of the $6,500 Chad owed Nick for product. They settled on $4,500 for the time being — all the cash she had on her — and the balance would come later.

Ragan enjoyed herself throughout the transaction.

“It’s great being a girl in this business,” she said on her way out. “It’s so easy to sell. People think I’m less likely to f – – – them over. And guys especially like buying drugs from me.”

She got on the subway, headed towards the East Village. She was quiet and admitted she felt shy talking about herself in an official, on-the-record capacity.

Ragan has reason, of course, to be worried about the legal implications of her activities. A first-time offender caught carrying more than 25 grams of Molly can face up to 10 years in prison; a second-time offender gets up to 14-year sentence.

But the financial rewards for dealing are hard to resist.

Though she makes $40 an hour teaching SAT classes and tutoring kids in their math classes, most of her income comes from dealing ecstasy. It’s a year-round business, but summer is especially lucrative. “High season,” she calls it. Much of the spike in demand is driven by music festivals — a common venue for dropping ecstasy.

Ragan runs Molly for Chad for a few hundred dollars a week. She makes most of her cash doing deals of her own with customers, who buy mainly for personal consumption. She gets about an ounce at a time from Chad for $1,200 a pop. One ounce can make about 280 pills.

Always precise with her math, she marks up the drug between two and three times what she buys it for when selling it to her dozens of customers. Her earnings can vary, though; the market price of ecstasy tends to fluctuate.

Once she arrived at her East Village subway stop, Ragan went to meet with Nick. She never said much about the extremely private Molly mover, except that she thought he was cute.

“I think drug dealers are sexy, though,” she said sheepishly.

Nick arranged meet-ups with Ragan at random locations in the tri-state area. About an hour beforehand, he would call and tell her where to go. The meetings typically lasted 20 to 40 minutes, as they wandered around together. When she needed to hand him money, she would do so inside, say, a shopping bag.

The first time Ragan met Nick, she had to sit for half an hour at a random park bench. Over several months their rapport developed enough so he would accept money from her directly, saving Chad trips around the area.

His need for discretion stemmed from the fact he smuggled dozens of pounds of ecstasy across the Canadian border at regular intervals. His sources are three factories in and around Vancouver that, according to Chad, before the last year supplied much of the Molly for the greater areas of Chicago, Boston and New York. Nick was considered their New York branch.

Nick knew of 12 other Molly-making labs in British Columbia, but they were controlled by Vietnamese gangs and a notorious Chinese crime syndicate called the Triads. Nick tried to stay away from these groups — as Chad put it, “How long before you wanna get robbed?”

Once Nick would make a purchase, he transported the product by passenger train and kept his powder-filled suitcases nicely filed on the racks. He never lost a shipment, he told Chad.

Since the summer, though, Nick has been outsourcing the smuggling responsibility to his network of associates in Canada and the US.

Nick has offered Ragan up to $20,000 cash to sneak drugs from Toronto, moving her up the supply chain. His Canadian associates would hide the product in the tires of her car, and she would stay in the area a couple nights to evade border patrol suspicions. So far, though, she has declined. Getting busted drug smuggling could mean 20 years in jail.

When Nick gets a shipment, he moves the stash to an office space in a nice building in the tri-state region. Each pound costs Nick about $5,000 wholesale. And he charges Chad $13,000 to $15,000 per pound for the connect and transportation.

Selling 15 to 20 pounds a month — Nick sells a few extra pounds to outside dealers — he takes home $160,000 to $200,000 a month during peak times.

The street price for Molly can go for up to $150 a gram — that is, $4,250 an ounce or $67,200 a pound. But to manage legal risks, Chad sells 65% of his allotment to smaller dealers in ounce-size quantities.

He charges $1,400 for an ounce. At that rate, the pound that Nick bought in Canada for $5,000 sells for more than $20,000.

Multiply that by 15 pounds a month and 12 months a year, and it’s a $4 million business with eye-popping profit margins.

“I’m making a killing,” said Chad with an excited grin.

And, at the start of summer, due to a local shortage of good ecstasy, his profits had been fatter than ever.

A drought in Canada had led to a shortage of safrole oil, the main ingredient needed to produce Molly. According to Chad, the Vancouver labs ran dry and even California, a growing hub in the US, lacked the substance.

Police in Canada had been cracking down on all avenues of ecstasy production, and conservationists helped the cause by fighting against the harvesting of sassafras plants, whose root bark and fruit provide safrole oil.

Things got so bleak last year that Chad and Nick considered contacting an administrator of an online ecstasy forum; he offered to sell 10 gallons of the stuff for $60,000 a gallon. Ultimately, they decided not to pursue the offer out of fear that they might be stepping into a Drug Enforcement Agency trap.

The bottleneck led to a proliferation of adulterated Molly that included synthetic drugs called “bath salts” — crystals that when crushed into a powder and mixed the right way can pass for ecstasy, especially to the untrained eye. They look like epsom salts but otherwise have nothing to do with actual bath salts; they cause people to become hyped up, as with cocaine.

Chad found the development extremely worrisome.

“Bath salts is a crazy f – – – ing drug,” he said. “The comedown is terrible, so you keep going up and up until you eat someone’s face off,” a reference to the Miami guy thought to be high on bath salts when he devoured a homeless man’s face.

Chad jacked up his prices after testing more than 14 samples of Molly he bought from other dealers in New York. Only one of the samples contained any substantial MDMA — the rest of the testers had a random combination of stuff.

Synthetic chemicals like K2 Spice and bath salts have been on the rise the last few years as they make their way into the world from China, reports the DEA. Advances in chemistry and science have helped foreign labs create brand-new drugs in a few months compared to a few years.

“It’s totally terrifying. The active dose to get high on bath salts can be five times less than MDMA,” said Chad. He remembered watching an acquaintance eat half a gram of what he thought to be Molly — and then seeing the guy spiral into a long and paranoid bath-salt trip.

The American Association of Poison Control Centers reported 6,138 calls about bath salts in 2011, up from 304 in 2010.

The lack of real MDMA has only increased profit margins. Chad would score $100,000 on his last kilo of the summer.

“It just goes to show that nobody is gonna stop rolling. It’s such a huge part of the rapidly growing electronic music scene. People are just gonna do f – – – ed up drugs,” he says.

But MDMA shortages and the risk of serious prison time mean Chad and Ragan won’t be rolling forever.

He’s been saving up to start a novelty wine business over the past year. “Hipsters are going to eat my s – – – up!” he says with a big smile.

Ragan thinks about growing up to be a banker like a lot of her classmates. But she’s not really sure where she’s going or what she’s doing, and in all her uncertainty, she sounds like a lot of other twenty-something-year-olds. “I just wanna pay the rent,” she laughs.