Effects of NLS-133, a Potential Non-Hormonal "On-Demand" Male Contraceptive

Inclusion Criteria: 1. Male, age 18-55. 2. Normal physical examination and testicular volume \>15 cc 3. No significant medical history that would impact the safety of the study. 4. No current use of drugs that comprise NLS-133 5. Normal values on baseline hematology, blood chemistry and liver function tests and serum testosterone. 6. Normal baseline sperm parameters (semen volume \>1.4 cc, sperm concentration \>15 million/ml, motility \>40% and morphology \>4%). 7. Willing and able to comply with all study requirements and procedures. Exclusion Criteria: 1. History or evidence of erectile dysfunction. 2. Inability to produce semen samples in clinic setting. 3. Significant chronic or acute medical illness. 4. Previous or current ethanol or illicit drug abuse. 5. Evidence of significant underlying disease (based on results of the physical exam and the routine labs). 6. Known infertility or hypogonadism. 7. Planned or anticipated use of any prohibited medications during participation in the study. These include use of sex hormones for treatment, testosterone, anabolic steroids, retinoic acid (e.g., Accutane®), vitamin A, other drugs known to inhibit spermatogenesis, opioids, cocaine, methamphetamine, and/or the consumption of \>4 alcoholic beverages daily. 8. Presence of moderate-to-severe pulmonary or cardiovascular disease 9. Known active hepatitis B, hepatitis C, human immunodeficiency virus (HIV), or COVID-19 infection. 10. History of malignancy within 5 years before the Screening Visit, except fully treated and resolved non-metastatic squamous or basal cell carcinoma of the skin. 11. Known active chronic or acute infection requiring treatment with systemic antibiotics, antivirals, antifungals, antiparasitics or antiprotozoals during the Screening period. 12. Any other acute or chronic medical or psychiatric condition or laboratory abnormality that could increase the risk associated with study participation in the judgment of the investigator would make the participant inappropriate for entry into the study. 13. Participation in another investigational clinical trial within the last 30 days. 14. Participants who live in detention on court order or on regulatory action. 15. Related to sponsor or staff involved in the conduct of the study.