The isolation of testosterone — Adolf Butenandt and the 1935 Nobel
10 min read · Uplevel editorial
On the first of June, 1889, Charles-Édouard Brown-Séquard stood before the Société de Biologie in Paris and described what he had done to himself. He was 72 years old, a neurologist of considerable distinction — he had been Jean-Martin Charcot's predecessor at the Salpêtrière, he had described the hemisensory syndrome that still bears his name — and he had spent the previous months injecting himself with a fluid he had prepared from the crushed testicles and testicular blood of dogs and guinea pigs. He reported that he felt thirty years younger. His intellectual energy had returned, his physical strength had improved, his digestion was better. He could run upstairs. He could work longer hours.
He was probably wrong about what was causing it, and almost certainly right that something was happening.
Brown-Séquard's self-experiment was methodologically inadequate in ways that would be obvious to any contemporary researcher: no control condition, strong placebo motivation, self-reported outcomes, a 72-year-old man who wanted very much to feel better. The aqueous extract he was injecting almost certainly contained insufficient testosterone to have a pharmacological effect, a point that later biochemists confirmed when they calculated the concentration of hormone in testicular tissue relative to the volumes he described using. What he likely experienced was placebo effect. But the idea he planted in the scientific literature was not a placebo. He articulated, in formal academic terms, that the internal secretions of the gonads could act at a distance on the body's systems — that the testicle was doing something beyond reproduction. He called it organotherapy. He licensed an extract product called Spermine. European physicians began experimenting with testicular extracts in their patients. Brown-Séquard died five years later, his self-experiment remaining controversial, but the category he had opened did not close.
The 1920s and 1930s brought more rigorous approaches. Animal experiments had established that castration produced predictable physiological changes — atrophy of secondary sex characteristics, reduced muscle mass, altered behavior — and that these changes could be reversed by testicular tissue transplantation or extract administration. The masculinization effects were real and measurable. Something in the testis was producing them. Identifying and isolating that something required the tools of steroid biochemistry that were just becoming available: large-scale tissue extraction, crystallization methods, color reactions for identifying steroid structures. The molecule was likely a steroid, because the known hormonal steroids — estrogens had already been isolated, cholesterol was structurally characterized — gave a framework for what to look for.
Adolf Butenandt was 32 years old when he isolated androsterone, the first androgen, from 15,000 liters of male urine in 1931. He was working at the University of Göttingen, and the project required the kind of industrial-scale chemistry that made hormonal isolation during this period seem less like biology and more like extraction mining. Androsterone was not testosterone — it was a urinary metabolite of testosterone, less potent, and not the primary testicular secretion — but its isolation proved that male sex hormones were steroid molecules amenable to chemical characterization. The structure could be determined. The compound could be named.
The race to isolate testosterone itself — the primary androgenic hormone produced directly by the testes — converged rapidly in 1935. Butenandt, by then working in Danzig, isolated testosterone from bull testes in May 1935 and determined its structure. Leopold Ružička, a Croatian-born chemist at the ETH Zurich, achieved synthesis of testosterone from cholesterol within weeks, demonstrating both the structural relationship to other steroids and the pathway for producing the compound without animal glands. The two papers appeared in close succession in the Hoppe-Seyler's Zeitschrift für physiologische Chemie. The priority dispute between Butenandt's isolation and Ružička's synthesis was never fully resolved to everyone's satisfaction, but the Nobel committee awarded both men the 1939 Nobel Prize in Chemistry — Butenandt for his work on sex hormones (extending through progesterone and estrogen isolation as well), Ružička for his work on polymethylenes and higher terpenes that encompassed the steroid synthesis.
Butenandt declined to travel to Stockholm to accept the prize. The Nazi government had prohibited German citizens from accepting Nobel Prizes following Carl von Ossietzky's peace prize in 1935, and Butenandt complied — though he accepted the prize itself after the war ended in 1949, when the prohibition no longer applied. The institutional complications of conducting chemistry in Germany in 1935 are part of the record.
Testosterone was available as a pharmaceutical compound within the same year of its isolation. The first clinical applications were for hypogonadism — men whose testes were not producing adequate testosterone — and for certain cases of female breast cancer, where the hormonal milieu was believed to influence tumor behavior. The injections required frequent administration, because testosterone is metabolized rapidly and the early preparations lacked the esterification chemistry that would later extend duration of action. Testosterone propionate, developed in the late 1930s, gave three-day activity. Testosterone enanthate and cypionate, developed in the 1950s, gave one to two weeks. The formulation history is a series of attempts to extend the window between injections without sacrificing the physiological properties of the molecule.
The athletic doping history began in earnest in the early 1950s. Soviet weightlifters competing in the 1952 Helsinki Olympics were, according to later accounts, given testosterone injections by their team physicians. The American physician John Ziegler, observing this at the 1956 World Weightlifting Championships in Moscow, returned to the United States and worked with Ciba Pharmaceuticals to develop dianabol — methandrostenolone — an oral synthetic anabolic-androgenic steroid with enhanced anabolic properties relative to testosterone. The logic was to preserve testosterone's muscle-building effects while reducing its androgenic effects, which produced side effects undesirable in many contexts. The synthesis of anabolic-androgenic steroids proliferated through the 1960s and 1970s, tracking closely with the Olympic doping arms race and the bodybuilding culture that emerged in parallel. Most of these compounds are now Schedule III controlled substances in the United States; their safety profiles are not favorable at the doses used in doping contexts.
The medical history of testosterone replacement is distinct from the doping history and worth keeping separate. Hypogonadism — primary, secondary, or age-related — has a genuine pharmacological treatment in testosterone replacement therapy, which is FDA-approved in multiple formulations: injectable testosterone cypionate and enanthate, transdermal gels and patches, intranasal gel, subcutaneous pellets. The indication is documented testosterone deficiency with clinical symptoms: fatigue, low libido, reduced muscle mass, depressed mood, impaired bone density. The approved context involves blood testing, diagnosis, and monitored treatment. This is different from the optimization discussion, which concerns men with testosterone in the low-normal range rather than deficient, and where the evidence for benefit is less established and the regulatory context is different.
The off-label landscape around testosterone and aging has been contentious for two decades. Total testosterone declines by approximately 1 to 2 percent per year after age 30 in men. By 60, the average man has testosterone levels measurably lower than at 25, and many men in the low-normal range report symptoms that overlap with hypogonadism. Whether treating men with low-normal testosterone improves their symptoms and quality of life without unacceptable cardiovascular, prostate, or hematological risk is a question the literature has not yet fully answered. The Testosterone Trials, a series of seven coordinated trials completed between 2010 and 2016, demonstrated benefits in sexual function, mood, bone density, and anemia in older men with low testosterone — but the cardiovascular signal remains subject to ongoing study.
The peptide connection to testosterone is one of the more clinically interesting developments in this space. Testosterone replacement, while effective, works by adding an exogenous hormone that suppresses the hypothalamic-pituitary-gonadal axis. The brain reads adequate testosterone in the bloodstream and reduces its own signaling — LH and FSH production drops, testicular function declines, and sperm production is suppressed. For men who are not done having children, this is a meaningful concern. For men on testosterone replacement who experience testicular atrophy, it is an aesthetic and functional one. The alternatives that work through the upstream signal rather than the endpoint have attracted research attention: human chorionic gonadotropin (HCG), which mimics LH and stimulates testicular testosterone production while preserving testicular size and function; gonadorelin, a synthetic GnRH analog that stimulates LH and FSH release from the pituitary; and kisspeptin, the neuropeptide that sits upstream of GnRH release and represents the system's most proximal regulator.
The distinction between these approaches and direct testosterone replacement is philosophically similar to the distinction between sermorelin and exogenous growth hormone: one approach adds the hormone directly, bypassing regulatory feedback; the other amplifies the signal that drives endogenous production, preserving the feedback architecture. Neither approach is superior in all contexts — the right choice depends on what the person's goals are, whether fertility preservation matters, and what the clinical picture shows. But the existence of the upstream options reflects a more sophisticated understanding of the HPG axis than was available in 1935 when testosterone had just been isolated and the immediate pharmacological priority was simply getting the molecule into clinical use.
What the testosterone history teaches about hormone replacement as a category is something about the gap between discovery and clinical nuance. The isolation of testosterone in 1935 established the molecule and its pharmacological potential with remarkable speed. What took longer — and is still being refined — is the understanding of how to use it appropriately: in whom, at what doses, through what delivery mechanism, in what relationship to the axis it operates within. Brown-Séquard injecting dog testicle extract at age 72 and declaring himself rejuvenated was the crude version of a question that is still being asked more precisely ninety years later. The molecule is the same. The questions around it have gotten considerably harder.
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