NCI Dictionaries:
Transdermal 4-hydroxytestosterone:
A transdermal formulation containing 4-hydroxytestosterone (4-OHT), a steroidal aromatase inhibitor (AI) and androgen receptor (AR) antagonist, with potential antineoplastic activity. 4-OHT is largely converted into 4-hydroxyandrostenedione (4-OHA) and irreversibly binds to and inhibits aromatase, thereby blocking the conversion of androstenedione to estrone, and testosterone to estradiol. This may inhibit tumor cell proliferation in estrogen-dependent tumor cells. In addition, 4-OHT binds to the AR and may inhibit AR-mediated tumor cell growth. Aromatase, a cytochrome P-450 enzyme, is overexpressed in a variety of cancer cells; it plays a key role in estrogen biosynthesis. Compared to oral 4-OHT, the transdermal formulation allows for continuous release of 4-OHT into the bloodstream and prevents first pass metabolism by the liver.

NCI Drug Dictionary:
https://www.cancer.gov/publications/dictionaries/cancer-drug/def/transdermal-4-hydroxytestosterone

Erowid Experience Vault:
https://erowid.org/experiences/subs/exp_PMA.shtml

6 Beta Hydroxy Testosterone Safety Data Sheet (PDF 5 pages):
https://www.caymanchem.com/msdss/10008519m.pdf

4-Hydroxytestosterone is advertised as anabolic steroid and does not have any therapeutic indication. It is a synthetic anabolic - androgenic steroid and a derivative of testosterone that was never marketed. It has moderate anabolic, mild androgenic, and anti-aromatase properties and is similar to the steroid clostebol.