INTRODUCTION
For pharmacists wearing the white coat, medicines have always been associated with a sacred mission: saving lives. However, throughout the history of modern medicine and law, there has been a darker side in which pharmacological knowledge has been fundamentally repurposed to serve the opposite goal: ending human life.
This is the practice of lethal injection in capital punishment.
From a professional perspective, this method of execution is not merely a legal procedure. Rather, it involves a complex series of pharmacological effects, raising significant scientific, ethical, and medical controversies.
1. FROM CAPITAL PUNISHMENT TO LETHAL INJECTION
Throughout human history, methods of capital punishment such as hanging, firing squads, electrocution, and gas chambers have been associated with considerable violence and visible physical trauma.
In an effort to develop a supposedly more "humane" alternative, one that would minimize the suffering of condemned individuals and reduce the psychological burden on execution personnel, lethal injection was introduced.
First implemented in the United States in the late twentieth century, this method was subsequently adopted and standardized in several countries. As a result, an execution increasingly came to resemble a medical intervention performed in a hospital emergency room.
2. WHY ARE DRUGS USED TO END HUMAN LIFE?
Drugs are chemical substances capable of altering the physiological functions of the human body. Life depends on maintaining stable physiological parameters, including heart rate, respiratory function, and cellular membrane potentials.
When an active pharmaceutical ingredient is administered at doses far exceeding its therapeutic range, it can disrupt the body's homeostatic balance.
The pharmacological agents historically associated with lethal injection target three essential physiological systems through a cascade of effects:
Central nervous system suppression: Enhancing inhibitory neurotransmission and eliminating consciousness.
Neuromuscular transmission blockade: Preventing voluntary respiratory muscle activity.
Disruption of cardiac cellular membrane potentials: Interfering with normal cardiac electrical activity and potentially causing cardiac arrest.
Together, these effects produce a profound disruption of normal physiological function. Although the process may superficially resemble someone falling asleep, its underlying mechanism involves a series of forced biochemical reactions at the molecular level.
3. MOLECULAR PHARMACODYNAMICS AND CELLULAR TARGETS
Historically, the three-drug lethal injection protocol has provided an example of drug combinations based on different pharmacodynamic mechanisms and molecular targets.
Group 1: Central Nervous System Depressants – Sodium Thiopental
Sodium thiopental is an ultrashort-acting thiobarbiturate. Its primary target is the gamma-aminobutyric acid type A (GABA-A) receptor complex, a ligand-gated ion channel located on central nervous system neurons.
Mechanism of action:
The drug acts on GABA-A receptors in the brain, enhancing chloride ion (Cl⁻) channel activity. The resulting influx of negatively charged chloride ions causes neuronal hyperpolarization, reducing the ability of neurons to generate and transmit electrical impulses.
Pharmacological effect:
Central nervous system activity becomes profoundly suppressed, resulting in deep unconsciousness and coma.
Group 2: Nondepolarizing Neuromuscular Blockers – Pancuronium Bromide
Pancuronium bromide is a nondepolarizing neuromuscular blocking agent belonging to the aminosteroid class. Its primary target is the nicotinic muscle-type (Nm) acetylcholine receptor located at the neuromuscular junction of skeletal muscle.
Mechanism of action:
The drug acts as a competitive antagonist of acetylcholine at nicotinic receptors on skeletal muscle. By preventing acetylcholine from activating these receptors, it interrupts neuromuscular signal transmission and prevents muscle contraction.
Pharmacological effect:
Progressive skeletal muscle paralysis occurs, including paralysis of the diaphragm and intercostal muscles, resulting in respiratory failure.
Group 3: Potassium Chloride (KCl) – Cardiac Dysfunction Through Electrolyte Imbalance
Mechanism of action:
Under normal physiological conditions, intracellular potassium concentrations in cardiac muscle cells are substantially higher than extracellular concentrations. This gradient is essential for maintaining normal electrical activity and cardiac rhythm.
A substantial disturbance in this potassium gradient disrupts the electrical properties of cardiac cells and their ability to generate and conduct electrical impulses.
Pharmacological effect:
Severe disturbances in cardiac electrical activity can result in the loss of effective cardiac contraction and cardiac arrest.
4. PHYSICOCHEMICAL INCOMPATIBILITY WITHIN THE VASCULAR SYSTEM
One significant technical limitation associated with the historical three-drug protocol involves pH-dependent incompatibility between sodium thiopental and pancuronium bromide.
Conflicting pH requirements
Sodium thiopental is a salt of a weak acid and requires a strongly alkaline environment for formulation, typically maintained using sodium carbonate (Na₂CO₃), to preserve its ionized, water-soluble form.
Pancuronium bromide is an alkaloid salt whose structure and stability are maintained under mildly acidic conditions.
Mechanism of precipitation
When the two solutions come into direct contact within an intravenous catheter or vascular line without an appropriate flushing procedure, the pH of the thiopental solution may decrease below the range required to maintain its solubility.
As a result, thiopental molecules become protonated and may transition from their soluble salt form into the poorly water-soluble free-acid form (thiopental acid).
Potential clinical consequences
Intravenous line obstruction: Precipitated thiopental acid may form visible white particles, potentially obstructing the delivery system or compromising vascular access.
Inadequate anesthetic exposure (underdosing): A portion of the drug may remain in precipitated form rather than being available in solution, reducing the amount delivered into the bloodstream.
Awareness under paralysis: Inadequate anesthetic exposure may leave an individual conscious despite profound muscle paralysis. The individual may experience severe pain and respiratory distress while being unable to move or communicate.
This phenomenon illustrates how physicochemical incompatibility can have consequences extending far beyond the formulation itself.
5. WHY DOES LETHAL INJECTION REMAIN A SUBJECT OF PHARMACOLOGICAL CONTROVERSY?
Although lethal injection was designed to produce a seemingly smooth and painless process, it has faced substantial criticism from the scientific and medical communities for several reasons.
Shortages of specialized pharmaceutical products
Major pharmaceutical manufacturers, particularly in Europe, have increasingly refused to supply medicines for execution purposes on ethical and humanitarian grounds.
Consequently, some US states have turned to alternative medications, including midazolam.
Midazolam is a benzodiazepine with sedative and anxiolytic properties. However, it is not equivalent to a barbiturate anesthetic in its ability to produce profound anesthesia. Its use has therefore raised concerns about the possibility that condemned individuals may remain conscious or experience pain.
The masking effect of neuromuscular blockers
Pancuronium produces muscle paralysis but does not provide analgesia or anesthesia.
If the initial anesthetic effect is inadequate, whether due to technical problems or individual variations in drug response, an individual may remain conscious while being physically unable to move.
This creates the possibility of experiencing severe respiratory distress and intense pain without being able to communicate or seek assistance.
The distinction between unconsciousness and physical immobility is therefore particularly important when evaluating the pharmacological and ethical implications of lethal injection.
6. PHARMACOLOGICAL VARIABILITY, INDIVIDUAL RESPONSE, AND THE CONCEPT OF A "HUMANE DEATH"
In pharmacology, the concept of interindividual variation is well established.
Each person has a different physiological profile, body weight, hepatic and renal function, and history of substance exposure, including alcohol or drug dependence.
Consequently, a standardized drug regimen may produce substantially different effects across individuals. A drug that is expected to produce a particular response may have a reduced or delayed effect in someone with significant pharmacological tolerance.
Furthermore, lethal injection is generally not administered by physicians or qualified nurses. Medical professionals may refuse to participate because of the ethical principles underlying medical practice, particularly the obligation not to intentionally end human life.
Instead, the procedure may be carried out by law enforcement personnel who lack specialized clinical training.
Technical errors involving vascular access, vessel damage, or infusion management have contributed to cases in which executions lasted for several hours and involved considerable suffering.
These incidents raise serious questions about whether lethal injection can genuinely be considered a humane method of execution.
7. WHEN PHARMACOLOGICAL KNOWLEDGE EXTENDS BEYOND THERAPEUTIC PURPOSES
The controversy surrounding lethal injection places pharmacology in a profound ethical dilemma.
Core principles of clinical pharmacology, including pharmacokinetics, pharmacodynamics, and drug interactions, are traditionally applied to optimize therapeutic regimens and improve patient outcomes.
However, in the context of capital punishm ent, these same principles have been investigated for the purpose of optimizing the process of death.
The development and testing of alternative drug regimens, including single-drug approaches involving high doses or the substitution of active pharmaceutical ingredients, have attracted criticism from bioethicists.
Some have characterized such practices as a form of unauthorized human experimentation, raising serious concerns about violations of fundamental human rights.
8. A PERSPECTIVE FOR PHARMACY STUDENTS
For future pharmacists, studying the pharmacological principles underlying lethal injection is not intended to provide a basis for its application.
Rather, it offers an opportunity to understand more deeply the delicate boundary between a medicine and a poison.
Dose and intended use are among the factors that determine the effects and consequences of a pharmaceutical substance.
Examining this darker aspect of pharmacology reinforces the importance of professional ethics in healthcare and pharmaceutical practice.
Knowledge is a powerful tool, but it must always be guided by professional integrity and human conscience, serving one fundamental purpose: protecting human health and preserving life.
REFERENCES
Malcom, D. R., & Romanelli, F. (2017). The Emergence of Second-Generation Lethal Injection Protocols: A Brief History and Review. Pharmacotherapy: The Journal of Human Pharmacology and Drug Therapy, 37(10), 1249–1257.
Kas, K., Yim, R., Traore, S., et al. (2016). Lethal drugs in capital punishment in USA: History, present, and future perspectives. Research in Social and Administrative Pharmacy, 12(6), 1026–1034.
Macdonald, R. L., & Olsen, R. W. (1994). GABA-A receptor channels: Biophysics and pharmacology. Annual Review of Neuroscience, 17(1), 569–602.
Sine, S. M. (2012). End-plate acetylcholine receptors: Structure, mechanism, and disease. Physiological Reviews, 92(3), 1189–1234.
Weiss, J. N., Qu, Z., & Shivkumar, K. (2017). The electrophysiology of hypo- and hyperkalemia. Circulation: Arrhythmia and Electrophysiology, 10(3), e004667.
Szedlak, P., Steele, D. S., & Hopkins, P. M. (2023). Cardiac muscle physiology. BJA Education, 23(9), 350–357.
Morton, W. D., & Lerman, J. (1987). The effect of pancuronium on the solubility of aqueous thiopentone. Canadian Anaesthetists' Society Journal, 34(1), 87–89.
Glossip v. Gross, 576 U.S. 863 (2015).
Romanelli, F., Whisman, T., & Fink, J. L. (2008). Issues surrounding lethal injection as a means of capital punishment. Pharmacotherapy, 28(12), 1429–1436.
Koniaris, L. G., Zimmers, T. A., Lubarsky, D. A., & Sheldon, J. P. (2005). Inadequate anaesthesia in lethal injection for execution. The Lancet, 365(9468), 1412–1414.
Philpott, S. (2014). Execution by Lethal Injection: Illegal Research? Hastings Center Report, 44(2), 11–12.
Authors:
MSc. Nguyễn Xuân Tú
MSc. Nguyễn Yên Hà
Publication date: November 6, 2026
