Guide to Endurance-Enhancing Drugs: EPO, HIF Stabilisers, Beta-Agonists & More (UK 2026)

Performance enhancement for endurance sports operates on entirely different physiological principles to anabolic steroid use for strength and muscle development. Where anabolic steroids target muscle protein synthesis, androgen receptor activation, and muscle hypertrophy, endurance-enhancing compounds primarily target oxygen delivery, lactate threshold, fat oxidation efficiency, and recovery from training-induced mitochondrial stress. This guide covers the major categories of endurance-enhancing compounds used by UK athletes.

Erythropoietin (EPO) and Erythropoiesis-Stimulating Agents

Erythropoietin is a glycoprotein hormone produced by the kidneys in response to hypoxia. Its physiological role is to stimulate red blood cell production in the bone marrow. Synthetic EPO (epoetin alfa, darbepoetin alfa) was originally developed for the treatment of anaemia in chronic kidney disease and cancer patients.

In endurance sports, supraphysiological EPO produces:

• Increased red blood cell mass and haemoglobin concentration
• Improved oxygen-carrying capacity
• Enhanced VO2max (maximal oxygen uptake)
• Improved lactate threshold

Performance impact: EPO administration in trained athletes has been shown to improve time-trial performance by 3–7% in controlled studies — a substantial margin in elite competition where winning margins are often fractions of a percent.

Critical safety concern: The most serious risk of EPO use is polycythaemia-induced thrombosis. Elevated haematocrit from EPO use (particularly the injectable, short-acting epoetin alfa) increases blood viscosity dramatically. Multiple fatalities among professional cyclists in the 1990s were attributed to EPO-induced thrombosis during sleep (when dehydration further concentrates the blood). Haematocrit monitoring is mandatory — do not use EPO without regular blood testing. Target haematocrit must remain below 50%.

Blood Doping and Blood Transfusion

Autologous blood doping (storing then reinfusing one's own blood shortly before competition) and homologous blood transfusion (using donor blood) both increase circulating RBC mass without pharmacological EPO. These approaches predate synthetic EPO and were the primary endurance doping method before the 1980s.

Autologous blood doping: no detectable marker (no foreign substance introduced); detected only through biological passport longitudinal haematological profiling by anti-doping agencies. The biological passport programme has significantly reduced but not eliminated blood doping in elite sport.

Altitude Training and Legal EPO Stimulation

Natural altitude acclimatisation produces the same erythropoietic stimulus as EPO — hypoxia stimulates endogenous EPO production and RBC proliferation. Athletes training at altitude (2000–3000m) or sleeping in altitude tents (hypoxic sleeping tents) achieve meaningful haematological adaptation without pharmacological intervention. This remains legal in competitive sport and is standard practice among elite endurance athletes.

Synthetic EPO Alternatives: HIF Stabilisers

Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF-PHIs) — including roxadustat, daprodustat, and vadadustat — are oral compounds that stabilise HIF-1alpha, the master regulator of the hypoxic response. This stimulates endogenous EPO production without requiring injection of exogenous EPO. HIF-PHIs were developed for anaemia of chronic kidney disease. They are prohibited by WADA in all sports.

Beta-2 Agonists

Beta-2 adrenergic receptor agonists are primarily used as bronchodilators in asthma treatment (salbutamol, formoterol, salmeterol). In endurance contexts, inhaled beta-2 agonists open the airways (bronchodilation), reducing airway resistance and improving airflow — particularly beneficial in exercise-induced bronchospasm. There is also evidence of modest performance enhancement beyond the bronchodilatory effect through sympathomimetic activity.

WADA regulations: Some beta-2 agonists are prohibited unless used via inhaler with a therapeutic use exemption (TUE) for documented asthma. Salbutamol is permitted via inhaler up to certain urinary thresholds. Athletes with genuine asthma can obtain TUEs for prescribed inhaled beta-2 agonists.

Meldonium (Mildronate)

Meldonium is a drug originally developed in Latvia for the treatment of ischaemic heart disease. It works by inhibiting the biosynthesis of carnitine — a molecule involved in fatty acid transport into mitochondria. The rationale for its performance use is complex: at low intensities, carnitine facilitates fatty acid oxidation (an efficient energy source); at high intensities, blocking this pathway increases glucose oxidation and reduces lactate accumulation, theoretically improving high-intensity performance and recovery. Evidence for performance enhancement in healthy athletes is limited and inconsistent. Meldonium became widely known when Maria Sharapova tested positive for it in 2016 following its WADA prohibition.

Growth Hormone and IGF-1 in Endurance Sports

HGH use in endurance athletes targets recovery, connective tissue adaptation, and fat oxidation rather than muscle hypertrophy. At 1–2 IU/day, GH-driven fat mobilisation and improved connective tissue integrity provide meaningful recovery advantages in high-volume training. The direct performance benefit in terms of VO2max or lactate threshold is less established than EPO's erythropoietic effect. See our HGH complete guide and HGH dosage guide.

Boldenone in Endurance Contexts

Boldenone undecylenate's pronounced erythropoietic effect (EPO stimulation) makes it of interest in endurance sports as well as strength sports. Its advantage over EPO in some athletic contexts is its anabolic steroid classification rather than direct EPO-class classification under WADA, though it is of course also prohibited in all competitive sport. Its RBC-stimulating properties require haematocrit monitoring identical to EPO protocols. See our boldenone complete guide.

Peptides for Endurance Recovery

BPC-157 and TB-500 are increasingly used by endurance athletes for managing the repetitive stress injuries (tendinopathy, stress fractures, muscle tears) that accumulate under high-volume endurance training loads. Their tissue repair properties are equally applicable to endurance athletes as to strength athletes. See our BPC-157 guide and TB-500 guide.

UK Legal Status of Endurance Enhancement Compounds

EPO and HIF stabilisers are not classified as controlled substances under the Misuse of Drugs Act 1971 but are prescription-only medicines (POMs). Their supply without prescription is illegal under the Medicines Act. They are prohibited by WADA in all competitive sports. For the full legal framework, see our UK performance drug law guide.

Frequently Asked Questions

Can recreational endurance athletes benefit from EPO?

Pharmacologically yes — EPO improves performance independent of baseline fitness level. However, the risk profile is not trivial, and the risk-to-benefit calculation for recreational athletes is very different from elite professional cyclists for whom marginal gains determine livelihood and career. The thrombosis risk is real and haematocrit monitoring is not negotiable. For most recreational athletes, optimising training load, nutrition, and legal altitude or hypoxic protocols offers meaningful performance improvement without EPO's risks.

Are there any legal supplements that genuinely enhance endurance?

Yes — beetroot juice/nitrate supplementation (improves oxygen utilisation efficiency; evidence-based); beta-alanine (buffers lactate at high intensities); sodium bicarbonate (acid-buffering, effective at very high intensities); caffeine (the best-evidenced legal ergogenic; 3–6 mg/kg improves endurance and time-trial performance reliably). These legal interventions produce meaningfully smaller effects than EPO but with no safety risk.