1-Testosterone (abbreviated and nicknamed as 1-Testo, 1-T), also known as δ1-dihydrotestosterone (δ1-DHT), as well as dihydroboldenone, is a synthetic anabolic–androgenic steroid (AAS) and a 5α-reduced derivative of boldenone (Δ1-testosterone).

[1] It was legally sold online in the United States until 2005, when it was reclassified as a Schedule III drug.

In vivo, an equimolar dose of 1-testosterone has the same potency to stimulate the growth of the prostate, the seminal vesicles and the androgen-sensitive levator ani muscle as the reference anabolic steroid testosterone propionate, but, unlike testosterone propionate, 1-testosterone also increases liver weight.

[2] 1-Testosterone, IUPAC name 17β-hydroxy-5α-androst-1-en-3-one, also known as 4,5α-dihydro-δ1-testosterone (Δ1-DHT) or as 5α-androst-1-en-17β-ol-3-one, is a synthetic androstane steroid and a derivative of dihydrotestosterone (DHT).

[3] Doping with 1-testosterone can be detected in urine samples using gas chromatography.