What Are Anabolic Steroids?

Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone, the primary male sex hormone. The term “anabolic” refers to their tissue-building effects (muscle growth, bone density, red blood cell production), while “androgenic” refers to their masculinising effects (deepening voice, body hair, male sex characteristics). Every anabolic steroid has both anabolic and androgenic properties, though the ratio varies between compounds.

It is important to distinguish anabolic steroids from corticosteroids such as prednisolone, hydrocortisone, or dexamethasone. Corticosteroids are anti-inflammatory drugs prescribed for conditions like asthma, arthritis, and allergic reactions. They do not build muscle, do not affect testosterone levels, and have an entirely different mechanism of action. When people say “steroids” in a bodybuilding or performance context, they are referring to anabolic-androgenic steroids, not corticosteroids.

A Brief History

Testosterone was first isolated and synthesised in the 1930s. By the 1950s, scientists had developed modified versions of testosterone designed to enhance its anabolic properties while reducing androgenic effects. Dianabol (Methandrostenolone), developed in 1955, became the first widely used oral anabolic steroid and was openly used by athletes throughout the 1960s and 1970s.

Anabolic steroids were initially used in legitimate medical contexts including treatment of hypogonadism (low testosterone), delayed puberty, muscle-wasting diseases (HIV/AIDS, cancer), severe burns, and anaemia. Many of these clinical uses persist today, particularly testosterone replacement therapy (TRT) for men with clinically diagnosed low testosterone.

By the 1970s and 1980s, anabolic steroid use had spread widely in competitive bodybuilding, powerlifting, and professional sports. This led to increasing regulatory attention and eventually to their classification as controlled substances in many countries.

How Anabolic Steroids Are Classified

Anabolic steroids are broadly categorised by their route of administration and chemical structure:

Injectable steroids are dissolved in oil and injected intramuscularly. They typically have longer half-lives and provide more stable blood levels. Examples include Testosterone Enanthate, Trenbolone Acetate, Nandrolone Decanoate (Deca), and Boldenone (Equipoise). Browse injectable steroids.

Oral steroids are taken by mouth in tablet form. Most are 17-alpha-alkylated to survive liver metabolism, which allows oral bioavailability but increases hepatic stress. Examples include Dianabol, Anavar, Winstrol, and Anadrol. Browse oral steroids.

Key Terminology

Cycle: A defined period of anabolic steroid use, typically 8 to 16 weeks, followed by a period off.

Stack: Using two or more compounds simultaneously during a cycle.

PCT (Post-Cycle Therapy): A protocol using drugs like Clomid or Tamoxifen to restore natural testosterone production after a steroid cycle. See our PCT Guide.

Aromatisation: The conversion of testosterone into estrogen via the aromatase enzyme. Some steroids aromatise (Test, Dianabol), others do not (Anavar, Winstrol, Trenbolone).

AI (Aromatase Inhibitor): A drug that blocks aromatisation to control estrogen levels during cycle. Examples: Arimidex, Aromasin.

SERM (Selective Estrogen Receptor Modulator): A drug that blocks estrogen at specific receptors. Used for PCT and gynecomastia prevention. Examples: Clomid, Tamoxifen.

Half-life: The time it takes for half of the active compound to be eliminated from the body. Determines injection or dosing frequency.

Ester: A chemical modification attached to the steroid molecule that controls its release rate. Longer esters (Enanthate, Decanoate) release more slowly and require less frequent dosing.

Anabolic vs Androgenic Ratio

Every steroid is measured against testosterone as the baseline, which has an anabolic:androgenic ratio of 100:100. Compounds with a higher anabolic-to-androgenic ratio are considered more “anabolic” (tissue-building with fewer masculinising effects). For example, Anavar has a ratio of approximately 322:24 (highly anabolic, low androgenic), while Trenbolone is 500:500 (extremely potent in both categories).

These ratios are determined through animal studies and serve as rough guides rather than precise predictors of human response. Individual genetics, dose, duration, and other compounds in a stack all influence the actual outcome.

Medical Context vs Performance Use

It is worth understanding that anabolic steroids have legitimate medical applications under professional supervision. When prescribed by a doctor for conditions like hypogonadism, the doses used are typically much lower than those used in performance enhancement, and the patient is monitored with regular bloodwork and clinical assessment. For more on this distinction, see our guide on medical uses of testosterone and anabolic steroids.

Non-medical use carries additional risks because doses are typically higher, multiple compounds may be combined, medical supervision is often absent, and the products used may come from unregulated sources. Understanding these risks is essential. See our guides on heart health, liver and kidney health, and hormones and fertility for detailed risk information.