Paul Clough’s job gives him a headache. The worst one went on for 14 straight days. Occasionally, his work causes him to develop a nasty rash on his back or arms. Sometimes he’ll throw up or get diarrhea. He’s been stuck with needles so many times that the crooks of his arms are covered in scar tissue. At times, he must wear a heart monitor. It’s not uncommon for his urine or feces to be inspected. And that’s all fine with him. As a person paid to help researchers collect data on new drugs, he accepts that certain unpleasantries come with the territory.

“It’s not that bad,” he says. “I mean, that’s why I’m there.”

Over the past 14 years, Clough, 39, who admits he’s a little out of shape these days but otherwise a healthy guy with an average build, has participated in more than a hundred clinical trials. His first was in Kansas City, Kansas. He’d been working as a day laborer, and the guy shoveling next to him said he knew a much easier way to make money. Clough spent three nights at a clinic, earned $600 for taking a series of capsules—and was hooked. Soon he was bouncing around the country’s regional research hotbeds, hitting clusters of clinics in New Jersey, Texas, and the Midwest. All told, Clough estimates, he has earned more than $400,000 as a professional test subject.

More than half a dozen times, Clough has made the trek to the Chicago area’s own hub for drug studies: the AbbVie Clinical Pharmacology Research Unit in north suburban Grayslake. The only major phase 1 clinic in Illinois, AbbVie’s site is regarded by many guinea pigs as one of the more pleasant places in the country to be confined while receiving repeated doses of experimental drugs. Set off along a wooded stretch of Route 45, the squat brick-and-concrete-block building resembles a midtier business hotel. And indeed, you could say it is, if you swapped out guests like traveling salespeople and conference attendees with men and women looking to make a few bucks while helping bring the next AndroGel testosterone booster to market.

Unlike later-stage testing, in which a medication is given to patients to test its effectiveness, phase 1 studies are simply about a drug’s safety (its side effects, how it’s metabolized in the body, that kind of thing), and that means trying it out on healthy volunteers. Most of the time, those volunteers are required to stay onsite, in an atmosphere that participants liken to a sleep-away camp for adults, for the duration of the trial, which could last from one day to several weeks. For this they are paid respectably—typically $200 to $300 a day.

“That first study, you either love it or you hate it,” says Clough, who lived in Chicago for a year before moving to Texas in 2015. “Some have an issue with cabin fever. Not me. I’m focused on the prize.”

AbbVie is a behemoth in the pharma world, ranked seventh in global drug sales. Formed in 2013 as a spinoff of Abbott Laboratories, the company is best known for Humira, an anti-inflammatory that treats conditions ranging from psoriasis to Crohn’s disease and had sales of $28 billion in 2017. At any given time, AbbVie’s scientists are working on dozens of new medications. The first step in moving them from the lab into the real world is the phase 1 clinical trial.

Finding that next blockbuster drug requires an army of volunteers. AbbVie declined to disclose how many studies it conducts annually, but typically its website is recruiting for half a dozen or so. Some trials are tagged by the condition the drug is supposed to treat, like Parkinson’s or psoriasis. Others are given only cute names like Winterberry and Daisy—codes for trials of medications intended to alleviate, say, rheumatoid arthritis or something vaguely menacing, like “tropical diseases.”

AbbVie touts altruism as a motive for volunteering. If chosen, “you will be participating in important health research and helping to advance scientific knowledge,” states its website. But the vast majority of test subjects get involved with phase 1 trials for another reason: They consider them easy money. Many are cash-strapped students. Some are between jobs. Others just need a little extra dough for a vacation or home improvement project.

And then there are “professionals,” like Clough, who travel the country from trial to trial, treating it as their job. “I’ve had issues with the law,” explains Clough, “and getting a traditional job is not the easiest.” (Of his criminal past, he says only that he “borrowed things from people and failed to return them.”)

There are whole websites and message boards (including the expected Reddit threads) dedicated to keeping these habitual volunteers aware of the latest moneymaking opportunities. The best known, Just Another Lab Rat!, was started by Clough in 2005 as a sort of TripAdvisor for the discerning test subject. It’s here that aspiring or veteran trial volunteers can share everything from advice on how to treat forearms swollen from needle pricks to insight on which clinics offer hot sauce in the cafeteria. The site also shares warnings about studies that some guinea pigs may want to consider carefully. (See the post alarmingly titled “Chemical Castration Study!”)

For Robbin Stewart, being a lab rat has become a second career. About 15 years ago, feeling burned out, the free-spirited public interest attorney closed his law practice. Now he makes enough money as a test subject—$20,000 in a good year—to subsidize other pursuits. While sequestered in clinical trials, he’s used the time to write court briefs for pro bono cases and craft blog posts about politics and soup recipes.

He’s done about 40 studies, driving from his home in Indianapolis to clinics around the country, including at least five at AbbVie. “I never thought I’d do it for that long. But it’s such an easy habit to fall into when they are offering you that kind of money and you’re not really doing anything. You just hang out for a few weeks or a month or whatever and get a nice check.”

The relatively comfortable accommodations at AbbVie are a draw for frequent participants. “Some other places are pretty industrial,” Clough says. “I like AbbVie because it’s never too crowded and is in a nice neighborhood. It’s almost like going to a retreat.” Ample closet space. A common area with a big-screen TV. Video games. And not one, but two billiards tables. These are some of the perks volunteers rave about. (AbbVie’s food doesn’t get such stellar reviews. Just Another Lab Rat! commenters call it “horrible” and “the worst”—especially the coleslaw and meatless lasagna.)

The confinement areas are clean and well-kept, says Clough. And he is typically in a group of eight or so subjects who bunk three to a room. (His website, which he sold a couple of years ago, puts the capacity of the clinic at 60.) During larger studies at different clinics, he might sleep in a room with 20 and be herded from blood draw to blood draw with a hundred other volunteers.

Rules are strict, however: Subjects must wear scrubs when not in their rooms; lights out at 11 p.m.; no foul language or porn; no outside food, candy, gum, or beverages; no electronics beyond small personal devices; security tape over smartphone cameras.

In between the battery of tests, subjects enjoy plenty of free time. They binge-watch TV (Clough says he saw five seasons of Lost over the course of a three-week study) or play cards or Scrabble. Stewart once organized a chess tournament. For about two years, Clough would pass the time between blood draws by making balloon animals, though he allows that wasn’t the best choice for a needle-heavy environment: “They popped a lot.”

It’s not all good times. Participants get routinely poked and probed and, of course, injected with medications that have never before been taken by humans. Though researchers have a fairly good idea how they’ll affect the body based on animal studies and their knowledge of the drug’s components, they don’t know for sure—and weird things do happen, like Clough’s two-week-long headache.

Ultimately, the question of what’s considered risky depends on one’s point of view, says Jill Fisher, a sociologist from the University of North Carolina currently working on a book about healthy test subjects. “Do you find it harmful if you are subjected to diarrhea and vomiting for a few days?” she asks. “I might, but someone else might be nonchalant about it. There is a lot of normalizing that happens when you talk with healthy volunteers. You’ll have somebody say something like, ‘I’d rather be paid $2,000 to have diarrhea than to have to pay for my lunch at a Chinese buffet and accidentally get it.’ ”

Even those who look critically at the industry acknowledge the trials are generally safe. “The problem is, catastrophic events happen,” Fisher adds. “They are rare but do happen, and they are shocking when they occur.” In 2006, for instance, six test subjects in London were rushed to the hospital and treated for organ failure. They survived but were told that over the long term, they’d likely develop cancer or an autoimmune disease as a result of a single injection of a drug intended to treat leukemia and arthritis.

Clough estimates he’s experienced adverse reactions roughly 10 percent of the time—the two-week headache being the worst. But he shrugs it off, saying there’s an upside to a drug’s having side effects that scare off other volunteer candidates: “It just gives me more of a chance to get into a study.”

Stewart is similarly unconcerned about the risk. “Most people ask, ‘Aren’t you afraid?’ Apparently, I lack that gene to be cautious and sensible,” he quips. He, too, has had very few bad experiences. But there was that time at AbbVie when a doctor struggled to get a tube down his nose and into his large intestine. “They had kind of a tricky time threading it through the stomach, so I was in there for 45 minutes while they were playing with the tube, trying to get it right,” he recalls. He says the clinic didn’t adequately warn him about the pain that would be involved. So he wrote a complaint—and has never since been selected for an AbbVie study.

Participants are not always forthcoming about adverse reactions, Stewart says, for fear of getting booted from a study. (He got kicked out of one recently after developing a rash—not because of the test drug, he thinks, but because of a cheap detergent he’d used. And he’s not happy about it. “It cost me $1,000.”) “You can get banned at any time, for any reason,” he says. “So if someone is experiencing a side effect, they are not going to run and tell the doctor. It’s bad science and bad policy—and defeats the whole purpose.”

Because of her medical background, Lesley Williams, a 39-year-old anesthesiologist who enrolled in trials at AbbVie and other clinics in 2012 and 2013 to help pay bills during her medical rotations at hospitals around Chicago, was in a unique position to evaluate the risks of the studies she participated in. “There are very few new drugs. Most are a spinoff of something else,” she says. “If the drug [I was considering testing] didn’t exist, I would cross-reference it with some equivalent.”

But even those studies that passed her litmus test weren’t exactly a stay at the Four Seasons. Like the time about five years ago at Spaulding Clinical in West Bend, Wisconsin, when she had her blood tested 20 times over two days. “It was insane,” she recalls. “After we took the medicine, we’d get our blood drawn every 20 minutes to see how it was being metabolized. You could get woken up at 3 a.m. and have them come in and draw your blood. Then you roll over and go to sleep when they’re done.” In another trial she participated in, one gauging the effect of a drug on heart rate, a volunteer had to leave the study after a strange read on an EKG. Williams says she did around 10 studies in total, collecting $20,000, and never felt in danger: “My thinking was, Even if I do something harmful, I know I am going to bounce back. We recover. That’s why [these tests] are done with healthy people.”

“Welcome to AbbVie,” says a perky and athletic-looking woman in jeans and running shoes. She ushers me to a couch in the lobby and tells me to make myself comfortable. “We’ll get to you as fast as we can.”

I’m here to see if I’m healthy enough to enroll in a clinical trial. AbbVie’s corporate folks had no interest in being interviewed for this story, so I had to go another route: undercover. A few weeks earlier, I’d called the recruiting hotline to volunteer for trials. After answering a series of questions about my health and medical history—from whether I was a smoker (nope) to whether I’d ever suffered a head injury (does the time I got hit in the noggin with a hockey puck in junior high count?)—I was told I qualified for an in-person screening.

The morning of my appointment, a diverse group of folks are spread out across the waiting room, which is decorated in muted browns and beiges. There are a few middle-aged suburban dad types in North Face jackets, some hard-­looking outdoorsy guys, a couple of young dudes in hoodies, and a lone woman who appears to be in her 50s. They sit reading the paper, watching the Today show, or staring straight ahead, waiting for their names to be called. I can’t help wondering: Who are these people, and why are they doing this? Are they going to use the cash to put in new kitchen countertops? Did they get a little over their head in last season’s fantasy football league?

For the next three hours, I fill out reams of paperwork: health questionnaires, consent forms, emergency contact sheets. Just passing AbbVie’s strenuous screening doesn’t guarantee you’ll get in a study. Most trials have their own definition of who is considered a “healthy individual”—and it can be quite restrictive. “Your weight has to fit the requirements,” says Williams. “Your labs have to be perfect. You can’t be drinking. You definitely can’t be doing drugs. A lot of people would do different types of detoxes to improve their chances of making it in.”

I’m a stocky 5-foot-7 nonsmoker and moderate drinker who safely (OK, barely) meets AbbVie’s body mass index requirements. I figure I’m a shoo-in. But it doesn’t take long for me to reevaluate my chances.

At one point, I tell one of the nurses that I took a multivitamin a day earlier, and she looks at me with great concern. Evidently, it could somehow mess up my screening results. But she decides to press on; I may be able to participate a few weeks later. I feel like I screwed up.

Clough estimates that he passes about 85 percent of his screenings. But he admits he hasn’t always been entirely forthright. If a researcher asks him the last time he had a drink, he’ll simply respond he doesn’t remember. His biggest stumble was when he bought a deep fryer. “I was frying everything,” he says. “It took me six months to get my cholesterol down.”

After my interrogation, I’m escorted into a well-lit lab surrounded by what looks like hundreds of vials of blood stored in crates. I get mine drawn, too. It will be screened for hepatitis, HIV, and high cholesterol. I pee in a cup. Then it’s off to an exam room for an electrocardiogram and a blood pressure test. During the former, the technician, a no-nonsense woman in her 40s, takes one look at my Teen Wolf–esque chest and suggests I do some manscaping prior to check-in if I make the cut. “They may not be able to get a reading quickly enough,” she says, explaining that my hirsuteness makes it difficult to apply the sticky electrode pads.

Finally, a doctor comes in—a friendly middle-aged man in a Mr. Rogers sweater—and administers a thorough physical. He moves my head back and forth. He shines a light into my eyes and ears. He listens carefully to my heart and lungs. I even have to do one of those walk-and-turn sobriety tests. By the end, I feel like a blue-ribbon contender at the state fair. He looks at my chart and learns that I am a first-time volunteer.

“Why do you want to do this?” he asks. I mutter something about the money. He gently tsks. “No,” he says. “These studies are for the good of society.”

After my screening is over, as I’m headed toward the door, I notice some of the AbbVie employees greeting a few of the would-be volunteers by name. There’s chitchat between a nurse and a guy in sweatpants and a baseball cap. “You’ve been here before, haven’t you?” she says.

While repeat customers and referrals appear to be essential to AbbVie’s ability to maintain a steady stream of volunteers, there are strict rules regarding frequency of participation. AbbVie insists that all test subjects observe either a 30-day “washout” period or the equivalent of five half-lives between studies to give a drug time to work its way through a subject’s system. But Clough says experienced guinea pigs know how to get around such restrictions. On Just Another Lab Rat!, there are several threads dedicated to the topic of which clinics share enrollment info among themselves. To rack up additional studies, Williams played whatever angles she could. For example, she befriended a veteran volunteer who gave her direct phone numbers for screening desks, which allowed her to avoid the busy signals of the main hotlines. “When you’re looking for the next study,” she says, “it’s a hustle.”

Like those of child actors and Olympic gymnasts, the careers of professional guinea pigs have expiration dates. Most trials seek people between 18 and 55. That means Stewart, at 57, is aging out of the game. “There’s just not many studies out there for people in my bracket,” he says. “And lately my blood pressure is a little high. It doesn’t seem to make sense to drive to Fargo for a study and find out I can’t get in.”

So what does he plan to do next?

“If it gets really bad, I can always go back to practicing law.” He’s also been flipping houses.

Williams has already moved on. She’s now finishing her anesthesiology residency at a hospital in Augusta, Georgia. But she doesn’t rule out returning to the clinic trial game in a pinch. “If it ever came down to it, I would absolutely do it again,” she says. “How many other places are going to pay you $200 a day? Hopefully, as an anesthesiologist it will never come to that.”

Even Clough is ready to give it up. He’s got a business idea in mind: He plans to sell fleece tails as fashion accessories to the cosplay community—“fidget spinners for your butt,” as he puts it.

“I need to do one more study,” he says. “That will give me the money I need for the summer.”

As for my own guinea pig career, a few days after visiting AbbVie, I get a message on my voicemail. I call the company’s rep back and find out I didn’t pass. Something about my ECG reading and a high white blood cell count.

I should probably get that checked out.