Anabolic:Androgenic Ratio
A 1950s–60s classification derived from the Hershberger rat bioassay. Abandoned by modern pharmacology for good reasons.
The anabolic:androgenic ratio is a 1950s–60s classification system derived from the Hershberger bioassay — castrated rat, compound-treated, two tissue endpoints measured after a fixed-duration course:
– Anabolic score: levator ani muscle mass vs. vehicle control
– Androgenic score: ventral prostate mass vs. vehicle control
Testosterone was assigned 100:100 as the reference compound; every other compound ratios against it.
Published ratios for common compounds:
– Testosterone: 100:100
– Nandrolone: 125:37 — higher anabolic, lower androgenic
– Trenbolone: 500:500
– Oxandrolone: 322:24
– Stanozolol: 320:30
– Methandrostenolone: 210:60
– Boldenone: 100:50
– Mesterolone (Proviron): 30:150 — androgenic with no meaningful anabolic effect
Why modern pharmacology has essentially abandoned the ratio:
Species translation failure. Rodent AR transactivation kinetics are not identical to human AR. A compound that activates rat AR maximally may show reduced activation in human cells due to receptor isoform and coactivator expression differences.
Tissue-endpoint limitations. The levator ani is a small striated muscle of the pelvic floor with fibre-type composition that does not match human limb or trunk musculature. Growth in levator ani does not predict growth in quadriceps; the correlation is weak even within rodent species.
Omitted mechanisms. The assay does not measure aromatisation, progestogenic activity, SHBG binding, glucocorticoid-receptor antagonism, 5α-reductase metabolism, or neuroactive metabolite generation. Trenbolone’s 500:500 looks balanced on paper; the actual human side-effect profile is dominated by progestogenic and neuropsychiatric effects that the rodent assay cannot detect.
Dose-range artifact. Ratios are derived at single doses. Non-linear dose-response curves — which all steroids exhibit to some degree — are invisible to the metric. A compound with clean ratio at assay dose may show degraded ratio at clinical doses used in practice.
What replaced it:
Modern pharmacology discusses AR affinity and dwell time, tissue-selective distribution, metabolite profile, and non-AR mechanism separately. The integrated picture — which dose of which compound produces which effect at which target tissue — is the framework now used in clinical endocrinology and the SARM research literature.
The A:A ratio retains some utility for rough comparison between DHT-derivatives and 19-nor compounds. It should not be used to predict clinical effect, side-effect burden, or dose equivalence between compounds with different pharmacophores. It is a metric from the era when pharmacology was a catalogue of animal-model observations. That has not been the state of the art for four decades.