Why does it come and go?
Finasteride use increases LH, and thus Testosterone output. Leydig cell hyperplasia can result from increased LH levels. Conflicting research says while this occurs in mice at very high dosages of the drug, it shouldn’t happen in humans. Wether thats true, who knows.
ajronline.org/cgi/content/full/180/2/501
"Adult patients with Leydig’s cell hyperplasia are usually asymptomatic [2]. However, some patients may present with testicular pain, swelling, or infertility "
"Although no one cause can account for all cases, Leydig’s cell hyperplasia is thought to be due to a faulty hypothalamic—pituitary—testicular axis with resultant chronic Leydig’s cell stimulation [2,3,4]. Because normal Leydig’s cells produce androgens as a result of luteinizing hormone stimulation, increased serum luteinizing hormone can result in Leydig’s cell hyperplasia. "
"In mice, 5a-reductase inhibitor therapy and prolonged estrogen exposure have been associated with Leydig’s cell hyperplasia ".
Leydig Cell Hyperplasia and Adenomas in Mice Treated with Finasteride, a 5-Reductase Inhibitor: A Possible Mechanism
toxsci.oxfordjournals.org/cgi/co … t/22/2/211
“In these studies, there was a positive correlation between the drug-related increased incidence of Leydig cell hyperplasia and a statistically significant (p 0.05) increase in serum LH levels in finasteride-treated (250 mg/kg/day) mice”
"The data presented support the conclusion that the effects of finasteride on Leydig cells appear to be secondary to increased serum LH levels and that they occur only at very high doses when compared to the therapeutic dose (approximately 0.1 mg/kg/day) in man. "
Leydig cell hyperplasia and adenoma formation: Mechanisms and relevance to humans
sciencedirect.com/science?_o … 512f7eb807
toxsci.oxfordjournals.org/cgi/co … t/22/2/211
“Androgen receptor antagonism, 5α-reductase inhibition, testosterone biosynthesis inhibition, aromatase inhibition, and estrogen agonism were considered to be relevant or potentially relevant, but quantitative differences may exist across species, with rodents being more sensitive.”