On April 29 a media frenzy erupted over a botched execution in Oklahoma. The story is now familiar: a doctor administered a three-drug cocktail to convicted murderer Clayton Lockett. He lost consciousness for a few minutes, according to eyewitnesses, then regained it, writhed in apparent pain, and cried out, “Oh, man.” Officials said it was the administration of the drug—not the drug itself—that caused the complication, but nonetheless, the incident turned international attention to the logistics of carrying out the death penalty.

The controversy spilled south to Texas, which has the country’s most active death chamber, where the next execution, of a man named Robert James Campbell, was scheduled for May 13. A federal court stayed Campbell’s execution over questions about his mental faculties, but news outlets around the world had already tied his story to the debate about lethal injection drugs.

The next Texas execution, of a man named Manuel Vasquez, is scheduled for August. He will be given a fatal dose of a single drug, pentobarbital, in a protocol the Texas Department of Criminal Justice has been using since 2012. Death penalty opponents will be looking for evidence that the drug causes Vasquez to feel pain, a violation of the Eighth Amendment’s ban on cruel and unusual punishment, while Texas prison officials, it is safe to presume, will be hoping for a smooth procedure so as to not invite the attention of journalists and activists.

Pentobarbital will take the stage again, and one question above all others will be asked of the drug: Is it a painless way to die?

Before pentobarbital developed its infamous reputation as a drug used in executions, it was just one of numerous barbiturates marketed to an American public hoping to fall asleep faster or to combat anxiety. Synthesized in 1928, pentobarbital rose to prominence when a Mayo Clinic anesthesiologist named John S. Lundy began administering Nembutal, the brand name for the drug, as an anesthesia for surgeries. In lower dosages, it eventually gained popularity as a sleep aid, an anti-anxiety drug, and a treatment for epilepsy and asthma. It was swallowed as a pill, inserted as a suppository, and injected. Ads from the fifties feature drawings of children too anxious to sleep and promised a “short but powerful hypnotic effect and prolonged sedative action” without a “morning-after hangover:”

     “When little patients balk at scary, disquieting examinations (before you’ve begun) . . .
      When they’re frightened and tense (and growing more fearful by the minute) . . .
      When they need prompt sedation (and the oral route isn’t feasible) . . . try
      Nembutal Sodium Suppositories”

As with nearly all barbiturates, overdose was a risk, and the drug received negative attention in 1962 after Marilyn Monroe was found dead at her home in Los Angeles. The autopsy report ruled her death an “acute barbiturate poisoning,” brought on by the interaction of pentobarbital and another sleep aid, chloral hydrate. Conspiracy theories flourished, but no matter what you might have believed about the star’s death, there was no denying that pentobarbital might not be the best thing to give your kid before bed.

After Monroe’s death, pentobarbital, along with other barbiturates, saw a decline in use in America. It was still used to treat certain rare forms of epilepsy and to induce comas, but once safer sleep aids hit the market, it wasn’t prescribed with the same frequency. Yet its ability to cause a peaceful, sleepy death became increasingly useful for one group of doctors: veterinarians.

For years now, drug makers have been selling pentobarbital to vets, promising “humane, painless, and rapid euthanasia,” as one label reads. It tends to be bright pink or blue so you can’t mistake it for something else. “It is thick and sticky,” described Danielle Hein, a veterinarian from Baltimore who regularly uses the drug for this purpose. “It feels like syrup if it gets on your hands.”

Veterinarians are confident that pentobarbital offers a painless death to animals if administered properly. Still, there are times when the animal’s body “maintains some non-cerebral reflexes” and thus appears to be in pain. “I once had an animal with no corneal reflex—meaning it was completely brain-dead—appear to sit up and cry out as it died, but it certainly was unconscious,” Hein told me. “It was really terrible to see, though, and it is hard to reconcile what you know to be true with what you see.”

As far back as the early eighties, prison officials around the country used a three-drug cocktail in executions: a barbiturate to knock the inmate out, a paralytic, and potassium chloride, which stops the heart. Then in 2011 the Illinois-based drug manufacturer Hospira Inc. announced that it would no longer be producing sodium thiopental, the barbiturate of choice for many executioners. The company had planned to shift production of the drug to a plant in Italy, but the Italian government—which opposes the death penalty—refused to license the facility to make the drug for use in executions. Arizona and California obtained shipments of the drug from England, but then that country too refused to allow further exports.

Prisons scrambled for a replacement. “We keep beating the bushes,” a Kentucky corrections officer wrote in a 2010 email. “Perhaps some pharmacy somewhere has some on the shelve [sic].” California sent their officials on a “secret mission” to obtain sodium thiopental from Arizona. This dearth of the drug prompted many states, including Texas, to switch from sodium thiopental to pentobarbital.

But procuring this alternative also proved difficult. In January 2014 Missouri corrections officer Dave Dormire testified, according to court documents, that he paid $11,000 for pentobarbital to a pharmacy he found in the Yellow Pages (“I take them cash,” he said in his sworn statement). The Colorado Independent discovered that in January 2011 Texas officials asked Oklahoma for advice on obtaining pentobarbital, an ironic twist considering that just one year earlier, Oklahoma needed sodium thiopental and Texas was of no assistance. “Looks like they waited until the last minute and now need help from those they refused to help earlier,” Oklahoma assistant attorney general Stephen J. Krise wrote to a colleague. “So, I propose we help if TX promises to take a dive in the OU-TX game for the next 4 years.” Another official from Oklahoma dubbed his colleagues “Team Pentobarbital” and said he would request, at one of these football games, “an on-field presentation of a commemorative plaque at halftime recognizing Oklahoma’s on-going contributions to propping up the Texas system of capital punishment.”

Where prison officials saw problems, opponents of capital punishment saw opportunity. For years, anti-death-penalty activists had tried futilely to stop executions with legal arguments and moral appeals to a pro-death-penalty American public. Now they had a new tactic—pressure drugmakers to choke off the supply. An activist named Maya Foa, working for the British anti-death-penalty group Reprieve, discovered that a Danish pharmaceutical company, Lundbeck Inc., was the only FDA-approved supplier of non-veterinary pentobarbital in the U.S. She made their name public, outing them as the provider of lethal injection drugs. Lundbeck expressed dismay and then sent letters to governors and correctional departments in sixteen states, including Texas, saying it did not want its pentobarbital used for executions. Then the company altered the distribution methods and made buyers sign documents promising not to resell the drug for use in executions.

Relentless pursuit of a new supplier eventually led Texas to a secret source. By July 2012, the state had such a large supply of the barbituate that when another one of the three execution drugs, pancurium bromide, expired, they developed a new protocol to administer a single, lethal dose of pentobarbital.

Officials, activists, and lawyers watched to see how the drug would fare in its solo act. Michael Graczyk, an Associated Press reporter who has witnessed hundreds of executions, told PBS the only difference was that it took a little longer for the condemned, in this case, a man named Yokamon Hearn, to die. “He was breathing deeply within the first seconds of the drug being administered and essentially went to sleep and began snoring,” Graczyk described. “And then the audio nature of the snores became less pronounced. And, finally, there was no noise and no movement at all.”

The Texas Department of Criminal Justice appeared to have devised a reliable system, and the state continued performing executions at a steady pace—two dozen from July 2012 to October 2013, when the Associated Press published the name of their most recent supplier: The Woodlands Compounding Pharmacy, near Houston. Other states had already come under fire for using pentobarbital obtained from compounding pharmacies, which are unregulated private operations that mix drugs to order and have been criticized for a lack of quality control. Harvard anesthesiologist David Waisel told Mother Jones that even tiny contaminants in pentobarbital from a compounding pharmacy could “cause an inmate immense pain in his veins” which could be “compared to rubbing sandpaper on an open wound.” Even veterinarians don’t always trust compounding pharmacies, according to Hein. (To address this problem, the TDCJ got an independent lab to test the pentobarbital the state was now buying in large quantities.) So when The Woodlands Compounding Pharmacy’s name went public, it immediately came under scrutiny. Their head pharmacist, Jasper Lovoi, was furious. “It was my belief that this information would be kept on the ‘down low’ and that it was unlikely that it would be discovered that my pharmacy provided these drugs,” he wrote in a letter to the TDCJ, demanding they return the drugs. The TDCJ refused, since they’d never signed a contract promising secrecy to Lovoi and the sale was final. Lovoi claimed to have received threats and harassment. He stopped selling to the TDCJ.

The department has since found a new supplier and has refused to release a name. Attorney General Greg Abbott, who initially supported transparency on the matter, reversed his stance in late May and sided with the prison system. He argued that the source of the drug could be kept secret since the state’s Department of Public Safety found evidence of threats to pharmacies selling the drug. “Pharmacies by design are easily accessible to the public and present a soft target to violent attacks,” DPS director Steve McCraw wrote in a letter to the TDCJ. None of these state agencies have divulged any more than that, and until a court rules that they must, none of them seem likely to do so. 

American prison officials aren’t the only ones hunting down reliable sources of pentobarbital. The New York Times reported in 2008 that men and women with chronic illnesses who want to commit suicide were illegally obtaining pentobarbital in Mexico and bringing it into the U.S. When Oregon passed the Death With Dignity Act, in 1997, it became possible for terminally ill patients in that state who want to end their lives to get prescriptions for pentobarbital (64 did in 2013). A few other states have also legalized assisted suicide, but in most of the country the practice remains illegal, and the terminally ill who want drugs for this purpose have to buy them from other countries. The problem is, when they purchase pentobarbital online or across the borders, there is no guarantee of effectiveness. 

“The question of drug purity in pentobarbital is becoming an increasingly important issue” for these types of patients, according to Dr. Philip Nitschke, a leading figure in the “aid-in-dying” movement. “We find that we are spending a lot of time trying to ensure quality so that people are reassured when they use the drug to end their lives.”

Nitschke developed a testing kit for pentobarbital and wrote The Peaceful Pill Handbook (banned in Australia, where Nitschke lives). He also created a machine that allowed his patients to administer the pentobarbital themselves. “If you press this button, you will receive a lethal injection and die in 15 seconds,” reads the screen. “Do you wish to proceed?”

Nitschke has spent much of his career developing a way to make death peaceful and painless. Both he and Dr. Jack Kevorkian’s longtime colleague Neal Nicol argue that pentobarbital is a viable solution (“incredibly peaceful,” in Nitschke’s words), but if you can’t find a reliable producer of the drug, you can’t guarantee painlessness.

This is why many find the secrecy of the TDCJ so disconcerting. If nobody knows who is making the pentobarbital and who is testing it, then nobody knows whether it will lead to a quick, painless death or an agonizing ordeal. After all, the one person who would be able to confirm or deny its efficacy isn’t capable of doing so.

In April triple murderer Jose Villegas was executed using the current stock of pentobarbital. As it began to flow through his veins, he noted, “It does kind of burn,” before gasping several times and falling silent.