Fluoxymesterone
Also known as: halotestin, halo
The 'halotestin' steroid: an extremely strong androgen with one of the worst safety profiles in this library.
Legal status: UK: Class C controlled drug and prescription-only medicine. Supplying it (including to friends) and importing it by post are criminal offences; personal possession for your own use generally is not. Checked 2026-07-26.
Prohibited in sport: Yes — on the WADA Prohibited List.
Approved medical use: Has been licensed for male hypogonadism and, historically, for some breast cancers.
What it is
Fluoxymesterone is a highly androgenic 17-alpha-alkylated oral steroid. It is used almost exclusively in strength and combat sports for its acute effects on aggression and perceived strength rather than for building tissue, and it is generally regarded even within that culture as one of the harshest compounds available.
Its licensed uses were in male hypogonadism and as a palliative treatment in some breast cancers, under supervision and with liver monitoring.
What’s claimed
- A sharp acute increase in strength and aggression before competition
- Extreme hardness and definition
- Little weight gain
What the evidence shows
It is genuinely a potent androgen, and the acute psychological effect people describe is consistent with that (Bronze: the human literature is old, clinical and small). What is not in dispute is the harm: fluoxymesterone is one of the most hepatotoxic anabolic steroids described, and its effect on lipids is severe. It offers little anabolic benefit to offset that, which is why it has no place outside the narrow niche it occupies.
The risks
- Hepatic: among the most hepatotoxic anabolic steroids described, with case reports of serious liver injury.
- Lipids: severe adverse lipid changes even over short periods.
- Psychiatric: strongly associated with aggression and mood instability.
- Endocrine: suppression of the body's own testosterone production, with testicular atrophy and impaired fertility. Recovery is not guaranteed and can be slow or incomplete.
- Androgenic: acne, male-pattern hair loss in those predisposed, and in women virilising effects, deepening of the voice, facial hair growth and clitoral enlargement, some of which do not reverse.
What needs monitoring
- Full blood count, including haematocrit and haemoglobin
- Lipid profile
- Blood pressure
- Liver and kidney markers
- Testosterone and the wider hormonal axis: a doctor is the right person to arrange these tests and to interpret what they show.
Sources
- NHS. Anabolic steroid misuse — health risks and the law.
- GOV.UK. Controlled drugs: Misuse of Drugs Act 1971 drug classes.
- World Anti-Doping Agency. The Prohibited List.
- Pope HG, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341-375.