The Drugs Used In Execution By Lethal Injection

Monday, May 19th, 2014

David Kroll explains the original three drugs proposed for lethal injection:

  1. a sedating drug to render the condemned unconscious (barbiturates such as sodium thiopental or pentobarbital)
  2. a neuromuscular blocking drug to cause paralysis of all muscles except the heart (such as pancuronium or vercuronium bromide)
  3. a lethal dose of potassium chloride to arrest the heart

He then addresses the drugs in reverse order:

Potassium chloride

Among the various salt ions that allow our bodies to function, one of the most tightly regulated is potassium. It’s required for all manner of nerve signals, proper brain functioning, and for the constant beating of the heart. The body keeps most of our potassium in cells with only a small fraction present in our blood. A large dose of potassium chloride introduced into the bloodstream, like that used in executions, would irreversibly paralyze the heart.

If given alone without the other drugs, the high concentration of potassium chloride would be terribly painful, akin to fire or electricity coursing through the veins.

Pancuronium, vecuronium, or other neuromuscular blocking agents

These drugs are modern relatives of the South American arrow poison, curare. They work by blocking the chemical signals from the brain and spinal cord that tell our muscles to contract. They act precisely where these nerves end at our muscles, hence the term neuromuscular blocker.

These drugs are most often used during surgery to allow a breathing tube to be inserted into the patient and to prevent involuntary muscle contractions during surgery. But the high dose used in executions is intended to stop the offender from breathing while also ensuring that the condemned appears completely still to the audience.

If given without the other drugs, it would be like having the worst night terror imaginable. You would experience oxygen hunger from being unable to breathe but be unable to move, all while being fully conscious.

Thiopental, pentobarbital, or other barbiturates

Barbiturates were first created in the early 1900s and were used intravenously throughout much of the last century to induce anesthesia, producing a loss of consciousness and an inability to perceive pain. They were then usually followed by an inhaled anesthetic for the maintenance of anesthesia. At lower doses, barbiturates were used to relieve anxiety in the years before the introduction of the safer benzodiazepine drugs: Librium (chlordiazepoxide) and Valium (diazepam).

For anesthesia, the barbiturates have largely been replaced by other safer drugs, usually in a combination that includes following: midazolam (Versed), an opioid like fentanyl, and a general sedative-hypnotic drug like propofol.

If given alone without the other drugs, a high dose of barbiturate alone could kill a person just fine. But it would take anywhere from 30 to 60 minutes. In fact, many drugs will cause death within an hour or two. However, corrections officials sought for execution to be rapid. This is why the sedating barbiturate was used in combination with the neuromuscular blocker and the potassium chloride.


  1. James James says:

    Why are neuromuscular blocking agents used? Seems to me that sedation and then stopping the heart would be sufficient. What purpose does paralysing muscles including breathing serve?

    The article describes a botched execution because they couldn’t find a suitable vein. Seems to me that hanging would be better.

  2. Isegoria says:

    The neurological blocking agents are for ensuring that the condemned appears completely still to the audience. Nobody wants an unpleasant execution.

  3. Space Nookie says:

    I was reading the other day that after the Revolution the Moscow Cheka was executing so many people that they ran out of bullets. Instead, they would rope their prisoners to cattle barges and then sink the barges in the river.

  4. Jay Dugger says:

    I wonder whether the three-drug cocktail increases, for want of a better phrase, the execution’s efficacy as a ritual, and eases the psychological effects on the executioners.

  5. James James says:

    Oh, so the cessation of breathing is just a side-effect.

    Space Nookie, I haven’t heard that one before but the French revolutionaries famously used drowning for mass executions.

    Wikipedia says the Khmer Rouge used pickaxes when they ran out of bullets. I seem to recall reading that they beat people to death with guns.

    Who was it that used one bullet to execute several people at once?

  6. Isegoria says:

    I believe Schindler’s List shows the Nazis lining up Jews in order to execute more than one person with each rifle shot.

  7. Isegoria says:

    Stalin’s chief executioner, Vasili Blokhin, almost single-handedly performed the thousands of executions of the Katyn Massacre, with a small-caliber German pistol, in a padded room with a sloped floor leading to a drain.

  8. Bruce Charlton says:

    Any one of the three drugs would be sufficient to kill on its own — the barbiturate would be the most pleasant (I knew of an anesthesiologist — that is to say an expert in these matters — who committed suicide with a barbiturate drip), the potassium chloride the fastest, the muscle paralyzing drug the worst.

  9. Isegoria says:

    As a non-expert, I assumed that an overdose of barbiturates would do the job painlessly, and that is how animals are put down humanely:

    Pets are almost always euthanized by intravenous injection, typically using a very high dose of pentobarbital or sodium thiopental. Unconsciousness, respiratory then cardiac arrest follow rapidly, usually within 30 seconds. Observers generally describe the method as leading to a quick and peaceful death.


    Some veterinarians perform a two-stage process: an initial injection that simply renders the pet unconscious and a second shot that causes death. This allows the owner the chance to say goodbye to a live pet without their emotions stressing the pet. It also greatly mitigates any tendency toward spasm and other involuntary movement which tends to increase the emotional upset that the pet’s owner experiences.

    For large animals, the volumes of barbiturates required are considered by some to be impractical, although this is standard practice in the United States. For horses and cattle, other drugs may be available. Some specially formulated combination products are available, such as Somulose (Secobarbital/Cinchocaine) and Tributame (Embutramide/Chloroquine/Lidocaine), which cause deep unconsciousness and cardiac arrest independently with a lower volume of injection, thus making the process faster, safer, and more effective.

    Occasionally, a horse injected with these mixtures may display apparent seizure activity before death. This may be due to premature cardiac arrest. However, if normal precautions (e.g., sedation with detomidine) are taken, this is rarely a problem. Anecdotal reports that long term use of phenylbutazone increase the risk of this reaction are unverified.

    After the animal has expired, it is not uncommon for the body to have posthumous body jerks, or for the animal to have a sudden bladder outburst. Unlike in films, the animal’s eyes do not usually close when it dies, and this has been stated purely as a drama display for pet death in movies (such as Marley & Me).

  10. Grasspunk says:

    Potassium chloride is used in salt substitutes. Seems kinda risky.

  11. Isegoria says:

    The dose makes the poison — well, the dose and the delivery method:

    Orally, potassium chloride is toxic in excess; the LD50 is around 2.5 g/kg (meaning that a lethal dose for 50% of people weighing 75 kg (165 lb) is about 190 g (6.7 ounces)). However, this is not far from oral toxicity of sodium chloride (table salt), of 3.75 g/kg, thus potassium chloride is harmless for alimentation (and even good for health, see previous paragraph). But intravenously, without the step of digestive absorption, this is reduced to just over 30 mg/kg.

  12. Grasspunk says:

    A lot of people try to reduce the salt in their diet. Maybe the inmates request salt substitute?

    LD50 is something, but what’s the lethal dose for 0.01%?

  13. James James says:

    Space Nookie, you were right. Wikipedia’s article on the “Red Terror” has the details.

  14. Windy Wilson says:

    Space Nookie and James James; I recall reading about some Einsatz Gruppen operation in Eastern Europe that tied Jews together two by two next to a high riverbank, and then shot one of each pair so that they would fall into the water to drown (if the shot one did not die outright, the unwounded one would definitely drown).

    The imagination of man to perform evil seems limitless; c.f. the Indians of the Ohio River Valley and the Toronto area of Canada with their torture methods. The Hurons were so called because that is a derivation of the French word for “the rough ones.”

  15. Toddy Cat says:

    Anyone who doubts the Christain Doctrine of Original Sin has never read history. The things that people will do to each other is simply astonishing…

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