For more than 6,000 years, farmers have known that castrating animals facilitates their domestication.7 In 1786, John Hunter performed the first testicular transplant from a rooster to a chicken. In the mid-19th century, experiments by Berthold also demonstrated that some substance in the testes was responsible for the growth of the comb and feathers in roosters, promoted their interest in the chickens, and increased their aggression toward other males. These characteristics were lost following castration only to be recovered after reimplantation of testicles onto the capons and even after a testicular transplant from another male.

Although the testicle is a testosterone-producing organ, it does not store it, unlike other endocrine glands such as the thyroids or pancreas. In addition, testosterone is inactivated by the liver when taken orally. Nevertheless, the consumption of testicles or extracts of it have been recommended since ancient times and in various cultures.

In contrast, castration—not taking to account social (eunuchs, slaves, harem guards), religious (castrati, or singing boys who were castrated to conserve the high ranges of a child’s voice, but with the lung power of an adult), or punitive reasons—was recommended as a treatment for various diseases such as lunacy, epilepsy, gout, priapism, and leprosy.

Brown Séquard (1817–1894), through his organ therapy, used extracts from the testes of pigs and dogs. Although his elixir contained truly homeopathic concentrations, he reported that it increased strength, mental capacity, and appetite. In addition, he stated that it cured constipation and, most of all, increased the length of the urinary stream. His product was a great commercial success, which led to various criticisms such as that of Harvey Cushing, who defined this practice as “endocriminology.”8 Oscar Zoth, winner of the Nobel Prize in Chemistry, together with his colleague Fritz Pregl were the first to use hormone extracts in athletes in 1869.

In 1929, the German Adolf Butenandt isolated the first sex hormone, estrone, and later the first androgen, androsterone, in the urine of a pregnant woman. He shared the 1939 Nobel Prize in Chemistry with Leopold Ružička. In 1935, Erns Laqueur and his collaborators isolated testosterone.

In 1950, athletes and body builders started to use testosterone and afterwards, in the 1952 and 1956 Olympic Games, the German and Soviet Union teams did. The magnificent results obtained by the German Democratic Republic after the 1960s, especially in women, notably attracted the public’s attention and, after demonstrating their link to anabolic steroids, the International Olympic Committee prohibited them in 1974.9,10 The most famous case of anabolic steroid abuse was that of Ben Johnson, who lost the gold medal he won after beating Carl Lewis the 100-meter dash finals in the 1988 Seoul Olympic Games for testing positive for stanozolol, a synthetic androgen.11

Since they have become commercially available, androgens, in addition to their use as replacement therapy in cases of hypogonadism, have demonstrated their benefit in some diseases such as anemia (before the introduction of erythropoietin), burns, growth with Turner syndrome, and wasting syndrome in HIV disease.12 At present, the main indication of androgen treatment is replacement therapy in organic male hypogonadism (hypothalamic hypogonadism, Kallman syndrome and variants, hypogonadotropic hypogonadism, primary hypogonadism, genetic-Klinefelter syndrome, etc.) and in transgender hormone therapy.

However, in recent years, testosterone prescriptions have multiplied in relation to the diagnosis of functional hypogonadism, which is linked to the concept of late-onset hypogonadism. Its use in this disease is doubtful and, what’s more, entails the possibility of androgenic dependence.13 A low testosterone level with proportionally low sex hormone-binding globulin levels together with normal follicle-stimulating hormone and luteinizing hormone values is characteristic of pseudohypogonadism, which occurs in obesity. Functional hypogonadism is not a disease and treatment with testosterone is not justified unless there is evidence of its safety and efficacy is shown in clinical trials.14

It is difficult to establish the frequency of use of androgens in the general population. Estimates vary widely (between 1% and 15%)15 depending, logically, on the population studied; the rate is not the same when comparing students and body builders. At present, only 20% of users are professional athletes.16

Indeed, 68% of short- and long-distance runners in the 1976 Olympic Games of Montreal who were asked recognized having trained with anabolic steroids for the 1972 Olympic Games of Munich, which took place before their prohibition; in another study, all the weightlifters did.17

A survey of university students in the USA and various European countries revealed a rate of anabolic steroid use between 1% and 5%.18 Another study on 6,000 Swedish adolescents revealed a figure of 2.8%–3.6% in males versus no cases in women.19 A meta-analysis of various studies in different countries indicated a prevalence of 6.4% in men and 1.6% in women,20 but there may have been over-representation of body builders, athletes, gymnasts, and prisoners in the sample.

In a German study, 13.5% of gym clients admitted to having taken anabolic steroids at some point, of which 3.9% were women.21 In another Iranian study, the percentage of body builders who had used some type of substance to enhance physical performance was 51.7% and of these, 79.4% used anabolic-androgenic steroids.22 A more recent study in a similar population found a rate of 36.2%.23

This disparity in results is due to the fact that many consumers hide their use either intentionally or out of ignorance.20 On the opposite end, false positives may be due to mistaking anabolic steroids with corticosteroids or dietary products.24

The main reason for using androgens is to increase muscle mass and strength and, in subjects who do not compete, to improve physical appearance or body image, or what is known as vigorexia.25 Users’ expectations of results are based on the recommendations of friends, trainers, or information on the internet. Those who purchase products on the internet do not know exactly what they are buying, as it may not contain any of these substances or be a dangerous product. The countries where the use of anabolic steroids is most frequent are the USA, Brazil, Australia, and the Nordic countries of Europe. However, use is much lower in China, Korea, and Japan, where culturally, a muscular appearance is must less valued in men.

Several specific types of anabolic steroid users have been described.26 Athletes have been consulted in various surveys about whether they would take a prohibited substance if it were not detected in order to win an Olympic medal (what is known as Goldman’s dilemma), and a high percentage responded affirmatively.27

Generally, athletes administer anabolic steroids by stacking, or progressively increasing the dose over 6–12 weeks in order to then decrease it in the second part of the cycle. Various anabolic steroids tend to be used simultaneously, reaching doses that are 40–100 times higher than physiological levels. We have even observed recommended regimens for gymnasts in which the only weekly change was in the brand name.

Another form of administration is cycling, which involves periods of use and rest. In the rest period, many use tamoxifen and hCG to try to recover or restore testicular function.13 Despite a lack of evidence, users believe these patterns of use lead to fewer undesirable effects and greater benefits.10,11

Although the substances used should ideally only act as anabolic steroids and not have any androgenic or virilizing effect, the reality is that all exert both actions to a greater or lesser extent. In future developments in selective androgen receptor modulators (SARMs), the effects may be selectively modified, as has occurred with selective estrogen receptor modulators (SERMs).28

Androgens can be administered as transdermal testosterone in gel or patches. Their half-life is short. Therefore, testosterone esters in the 17 ®-hydroxyl group are administered in oil form through the parenteral route of administration (propionate, enantate, cypionate, undecanoate) in order to prolong their activity.

The elimination of the methyl group in position 19 gave rise to 19-nortestosterone and derivatives (nandrolone decanoate and phenpropionate) with a greater anabolizing effect than virilizing effect. These directly bind to androgen receptors and, after aromatization to estrone and estradiol, also to estrogen receptors.29 A third type are alkylated compounds in the C-17-〈, which are administered orally. They include, among others, oxymetholone, oxandrolone, metenolone, methandrostenolone, and stanozolol, which generate a slow hepatic metabolism that explains their greater toxicity.

Another form of increasing the rate of circulating androgens is through the administration of drugs that increase their endogenous production. This group includes gonadotropins (luteinizing hormone and hCG), aromatase inhibitors (anastrozole, letrozole, exemestane), SERMs (clomiphene, tamoxifen, raloxifene, bazedoxifene, fulvestrant, etc.), and lastly testosterone precursors (4-androstenedione, 4-androstenediol, 5-androstenediol, and dehydroepiandrosterone) or precursors of the synthetic androgen nandrolone (norandrostenedione, 4-norandrostenediol, and 5-norandrostenediol).

The most commonly used androgens in the population are testosterone and boldenone or trenbolone. The latter are only indicated for veterinary use. Among the doping substances most commonly detected by WADA in competitive athletes are testosterone, stanozolol, and nandrolone, especially among weightlifters and boxers.2

Many users often combine various doping substances in what is truly polypharmacy: for example, anabolic steroids are combined with growth hormone and aromatase inhibitors or SERMs to avoid side effects such as gynecomastia; thyroid hormones to lose weight are combined with diuretics that also serve to prevent its detection. What’s more, others are used with opioids and alcohol.30

The main effect of androgens is muscle hypertrophy due to an increase in both type i and type ii muscle fiber thickness, the number of capillaries, and the number of myocyte nuclei per fiber, which could produce an increase in muscle strength.31 The increase in protein synthesis with a positive nitrogen balance produces a gain of up to 37% when combining testosterone and exercise and only 10% with testosterone without exercise.32

This dose-dependent muscle hypertrophy is manifested more in the muscles of the neck, shoulders, thorax, and arms due to a greater number of receptors; they return to their initial size after 12 weeks of suspension. The increase in muscle strength is not unanimously accepted by the scientific community33 and is truly small and variable. Studies show conflicting results. In addition, there are few studies in women. Results in endurance sports, such as cycling, have also not been demonstrated.

Table 2 summarizes the adverse effects due to consumption of anabolic-androgenic hormones. Most data have been obtained from case-control studies and, given the aforementioned polypharmacy, cannot always be attributed to androgens.

Anabolic steroid use may be suspected due to clinical signs (muscle development, acne, sexual dysfunction, and gynecomastia in men; androgenetic alopecia and hirsutism in women) and analytical data (suppression of gonadotropins, high testosterone levels, decrease in HDL cholesterol).

The implementation of Athlete Biological Passports by the WADA in 2009 was an important step for control, as it guarantees updated confirmation that the athlete has not consumed prohibited substances.63,64

For cases of legal use due to previous hypogonadism (therapeutic use exemption), it must be taken into account that the minimum washout period is two weeks for transdermal or gel testosterone, four weeks for oral undecanoate, eight weeks for intermediate-duration esters (enanthate cypionate) and 26 weeks for prolonged-action esters (injectable undecanoate), and up to 40 weeks for subcutaneous testosterone pellets. These periods tend to be longer if the doses are greater than physiological doses.65

The testosterone:epitestosterone ratio has also been used to detect doping. Epitestosterone is an isomer that segregates jointly with testosterone and is inactive. There is no conversion from testosterone to epitestosterone or vice-versa. The normal value of the testosterone:epitestosterone ratio is close to 1:1. A value greater than 6:1 is indicative of exogenous administration. The result can be masked with the simultaneous administration of epitestosterone.

The testosterone:epitestosterone ratio is also not valid in women because in women, androgens come from the ovaries and adrenal glands.66 Therefore, other detection methods are needed, such as mass spectrometry and bioassays, which are easier and more economical, though they have the limitation of their standardization.6,12 Another possibility is the use of biological matrices such as the hair, skin, saliva, or nails.67

Finally, regarding doping with indirect androgens, the following can be used: 1) testosterone precursors such as dehydroepiandrosterone and androstenedione; 2) gonadotropins; and 3) estrogen receptor antagonists and aromatase inhibitors.

Androstenedione is produced in the gonads and adrenal glands from dehydroepiandrosterone and is converted to testosterone via 17®- hydroxysteroid-dehydrogenase. Both androgens elevate testosterone levels and increase the testosterone:epitestosterone ratio. It can also be detected via mass spectrometry. The effect on muscle strength that gonadotropins produce is scarce. Recombinant luteinizing hormone and hCG require injectable administration several times a week and are expensive. Both can be detected via immunoassay or mass spectrometry,68 although it is not valid to investigate hCG in women due to ethical reasons, given that it increases physiologically in pregnancy.

The described side effects of hCG are hyperglycemia and insulin resistance, decrease in thyroid function, adrenal insufficiency, carpal tunnel syndrome, arthralgia, myopathy, pancreatitis, hepatotoxicity, and possibility of neoplasms.48

The use of antiestrogens and aromatase inhibitors is based on the fact that estrogens are much more potent in inhibiting the gonadal axis. All of these have been prohibited by WADA since 2008, as are new SARMs. These modulating agents with specific action on different androgenic receptors are a field for future research in the development of new molecules indicated for various diseases12 in which possible toxicity must be evaluated.69