The goal of this clinical trial is to evaluate three doses of the drug leflutrozole on improvement of semen quality in men. It will also study the safety of leflutrozole.

The main questions it aims to answer are:

• Does leflutrozole improve semen quality?
• What medical problems do participants experience when taking leflutrozole?

Researchers will compare leflutrozole to a placebo (a look-alike substance that contains no drug).

Participants will:

• Take leflutrozole or a placebo orally once a week for 16 weeks.
• Visit the clinic every 4 weeks for checkups and tests.
• Provide semen samples to measure changes in semen quality.
• Have their blood tested to measure hormone levels and ensure safety.
• Be monitored for any side effects.

Inclusion Criteria:

• Signed informed consent form prior to any-related trial activity.
• Adult men aged 18-49 years (both inclusive).
• Low serum total testosterone concentration on two occasions.
• Serum estradiol (E2) level within or above normal range at screening.
• Serum Luteinizing Hormone level within or below normal range at screening.
• Low total motile sperm count in two samples.
• Semen volume ≥1.0 mL in two samples.
• Ability to understand and comply with the requirements of the protocol.

Exclusion Criteria:

• Anatomical abnormalities of the testes or malignant or benign tumors of the testes.

• Pituitary or hypothalamic disease.

• Prostate disease.

• Treatment with one or more of the following prescription drugs or over-the-counter medications or supplements for 6 months prior to the screening visit:

  1. Compounds with androgenic or estrogenic properties (i.e., agonist or antagonist) or that affect production of sex hormones.
  2. 5-α reductase inhibitors, e.g., finasteride and dutasteride.
  3. Fertility drugs, including clomiphene, FSH, hMG and hCG preparations.
  4. Growth hormone.
  5. Opioid-receptor antagonists, e.g., naloxone and long-acting opioids.
  6. Selective α-adrenergic-receptor antagonists (alpha blockers).
  7. Topical or systemic testosterone replacement therapy (TRT).
  8. Anabolic steroids.

• Inability to reliably produce the required semen samples for trial assessments due to significant erectile dysfunction, anorgasmia, or other reasons.

• Participation in any clinical trial using clinical intervention within 3 months before the screening visit or 5 half-lives of investigational product administration, whichever is shorter.

• Any clinically significant 12-lead ECG abnormalities at screening.

• Known history of thromboembolic disease.

• Grade 3 lower extremity edema.

• Known cardiovascular disease.

• Known history of osteoporosis or fragility fractures.

• Known moderate or severe impairment of renal or hepatic function.

• Untreated diagnosis of sleep apnea.

• History of cancer within the last 5 years.

• Known alcohol and/or drug abuse within the last 12 months prior to randomization or evidence of such abuse indicated by the laboratory results during the screening assessments.

• Known chronic opioid use and/or misuse within the last 12 months prior to randomization.

• Any psychiatric or medical disorder or circumstance, which in the investigator's opinion might jeopardize participant's safety or compliance with the protocol.

• Hypersensitivity to any active ingredients or excipients in the medicinal products used in this trial.