Table 2. Study characteristics related to number of participants, inclusion and exclusion criteria, type of interventions, type of outcomes, and follow-up.
	Author, year
	Clark & Sherins, 1989	Gregoriou et al., 2012	Cavallini, 2013
Location	Atlanta, USA	Athens, Greece	Andros, Italy
No. participants	25	29	46
Inclusion criteria	Men that were partners in infertile marriages in which there was failure to conceive for at least two years prior to consideration of entry into the protocol	Men with low T/E2 ratio (<10)	Non-smoker non- obstructive azoospermic (NOA) patients who yielded no spermatozoa with fine needle and cryptozoospermic patients with T/E2 ratio < 10
Exclusion criteria	Men with known exposure to testicular toxins, including chemotherapeutic agents, radiation, industrial chemicals, pesticides and excessive alcohol intake, and patients with a clinically apparent varicocele, history of cryptorchidism or mumps orchitis, evidence of hypogonadotropic hypogonadism, or a demonstrable chromosomal abnormality.	Not reported	Seminal white blood cell concentration greater than 106 ml and/or a positive seminal cultural analysis or positive urethral swab chlamydia test; drug tobacco, or alcohol abuse; on going medical treatment (gonadotropins, anabolic steroids, cancer chemotherapy, non steroidal anti inflammatory drugs; previous cancer radiotherapy or chemotherapy, palpable varicocele; X-ray exposure in the previous 8 months; Y chromosome microdeletion, and karyotype alterations if Klinefelter syndrome
Type intervention	Each patient received testolactone 500mg orally four times per day or placebo (gelatin capsules containing cornstarch) for eight months, followed by an alternate therapy for an additional eight months.	Intervention group consisted of 2.5 mg letrozole (n=15) or the control (n=14) groups with 1 mg anastrozole both taken orally once daily	Patients were randomly assigned treatment to receive either letrozole 2.5 mg once a day or placebo (starch 100 mg once a day)
Type of outcomes	Total estradiol and testosterone levels during testolactone exposure; sex hormone binding globulin (SHBG) capacity and free E2; LH and; FSH serum concentrations	Serum FSH, LH, prolactin (PRL), T, and E2 levels and; total motile sperm count - ejaculate volume x concentration x motile (fraction)
Follow-up (months)	16	6	8