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PLOS BLOGS Speaking of Medicine and Health

“Pulling Back the Curtain” on Lethal Injection

PLOS Medicine Associate Editor, Thomas McBride, reflects on the 2007 research article that investigated whether lethal injection consistently induces a painless death.

Image credit: Joseph Kranak, Flickr
Image credit: Joseph Kranak, Flickr

The December 7, 1982 execution of Charles Brooks Jr. in Texas marked the first use of lethal injection, conceived as a painless and more “humane” alternative to the electric chair. With the patient laying on a gurney, heart monitored by an ECG and an IV drip in arm, the new procedure certainly looked like a controlled death delivered by medical science. Over the next three decades lethal injection would become the most common form of execution in the United States and worldwide. But when reports of complications arose, the public and lawmakers began to question whether inmates were being forced to needlessly suffer. By 2006, 11 states had suspended executions while they considered changing the protocol. In a 2007 PLOS Medicine research article, Leonidas Koniaris and colleagues asked whether lethal injection truly delivers a consistently painless execution.

The article was an interesting choice for a medical journal. Despite appearances, lethal injection is anything but a controlled medical environment. Ending the life of a physically healthy person against his or her will is antithetical to medicine, which is why the technician who attaches the IV is not a doctor or nurse. The protocol was designed not based on experimental evidence, but the personal experience of Oklahoma state medical examiner Jay Chapman. Academic editor Clifford Woolf recalls the decision to publish was a “tough call, since it could be argued the paper better belonged in journal specializing in ethical or legal issues.” In an Editorial that ran in the same issue, the PLOS Medicine Editors expressed hopes that the data presented in the research article would convince US lawmakers that execution is inhumane.

The topic was also a departure from the norm for Koniaris and his colleagues, primarily cancer researchers. Lead author Teresa Zimmers recalls it was difficult to fit this research around their “day jobs” but that despite the sacrifices, they were “excited to add knowledge about the process and to help shape the debate.”

Adding to the authors’ difficulty, while lethal injection has been practiced in 37 different states, and a number of states collect data on their executions, only a few states release this information. The authors worked with what they could get their hands on. The states who did allow the researchers access to data all used versions of the three drug protocol originally devised by Chapman: 1) The fast acting anesthetic sodium thiopental, expected to render the inmate unconscious and induce death “within 1-2 minutes” by depressing respiration. 2) The paralytic pancuronium bromide, which should also stop respiration. 3) Potassium chloride, which should produce cardiac arrest. It was thought that any of the three drugs would be lethal on their own; the only reason to use them in combination was redundancy.

Data from executions told a different story. Koniaris and colleagues found executions that questioned the effectiveness of each of the drugs. Using data on body weight from the North Carolina Department of Corrections and the known pharmacokinetics of sodium thiopental, close to the range used for surgical anesthesia, and not enough to induce death on their own. Data on the time course of executions from California supported this interpretation, as some inmates continued to breathe up to 9 minutes after thiopental was injected. In other cases, breathing continued after pancuronium bromide administration, and the heart continued to beat after potassium chloride was given.

If neither the thiopental nor the potassium chloride doses can reliably produce death, respiratory cessation from pancuronium bromide was likely the cause of death in some inmates. This was almost certainly true in cases where the IV line was misplaced, pancuronium bromide being the only drug of the three that is effective when delivered intramuscularly or subcutaneously. Koniaris and his colleagues presented the possibility that some inmates were awake but paralyzed through some of the execution procedure, conscious as they suffocated to death. The authors’ call for more states to release the execution data they had collected echoes PLOS’ dedication to open access.

Though it was not a typical article for PLOS Medicine, its timeliness and the political nature of the topic likely drove the attention (over 21,000 views in its first year and 50,000 views through October 2014). Not everyone agreed with Koniaris and colleagues. There are some people who are not sympathetic to the suffering of those convicted of murders, and comments made on the article make it clear that their support of the death penalty is unwavering. In 2008 the US Supreme Court upheld Kentucky’s method of lethal injection against a challenge that it violated the 8th Amendment’s ban on cruel and unusual punishment. However, in Justice Ginsburg’s dissenting opinion, she pointed out the potential the inmate would not be unconscious during the injection of the second and third drugs “poses an untoward, readily avoidable risk of inflicting severe and unnecessary pain.”  An unintended consequence of the article was a call for research into better methodology; in a 2008 PLOS Medicine Essay, Koniaris and Zimmers argued such research crosses a line into unethical human experimentation.

And while lethal injections were approved to continue, the companies that formulate the sodium thiopental refused to supply it for use in lethal injection based on moral opposition. The supply shortage has delayed executions and some states are now adopting different drug protocols. Reflecting on this work and its impact, Dr. Zimmers expresses pride: “I feel we helped pull back the curtain on the shoddy medical charade that masqueraded as a humane death.” PLOS Medicine agrees and is proud to have played our part to provide this information to the public.

You can read the full research article here:

Zimmers TA, Sheldon J, Lubarsky DA, López-Muñoz F, Waterman L, et al. (2007) Lethal Injection for Execution: Chemical Asphyxiation? PLOS Medicine 2007


This is post 5 of 8 in PLOS Medicine’s 10th Anniversary blog series on the most interesting and influential articles of the last ten years.You can find links to all the posts in the series as they are published here.


  1. The conclusion was this:

    “Koniaris and his colleagues presented the possibility that some inmates were awake but paralyzed through some of the execution procedure, conscious as they suffocated to death.”

    Almost anything is possible and that defines the importance of the speculation.

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