This is a Phase 2a, double-blind, placebo-controlled, crossover study evaluating the efficacy, safety, and patient-reported outcomes of KH-001 in men with lifelong premature ejaculation (LPE). Approximately 40 participants will receive KH-001 or placebo in two 4-week treatment periods separated by a washout.

This Phase 2a, multicenter, double-blind, placebo-controlled, crossover study is designed to evaluate the efficacy, safety, and patient-reported outcomes of KH-001, a selective serotonin transporter (SERT) inhibitor, in men with lifelong premature ejaculation (LPE). Approximately 40 participants will be enrolled across sites in Australia. Each participant will receive both KH-001 and placebo during two separate 4-week treatment periods, with a 4-week washout in between. KH-001 will be administered sublingually as an orally disintegrating tablet (ODT), taken on demand 15 minutes before vaginal penetration, with intake limited to one dose (2 tablets) per day. The primary endpoint is change in intravaginal ejaculatory latency time (IELT). Secondary endpoints include assessments of patient global impression, premature ejaculation profile, and safety parameters.

Inclusion Criteria:

1. Male participants aged 18 to 65 years (inclusive) at the time of informed consent.
2. In a stable (≥6 months) monogamous heterosexual relationship.
3. Self-reported lifelong premature ejaculation (LPE), meeting the ISSM definition.
4. Intravaginal Ejaculatory Latency Time (IELT) ≤1 minute on at least 75% of intercourse attempts during the 4-week run-in period.
5. PEDT (Premature Ejaculation Diagnostic Tool) score ≥11.
6. Normal erectile function (IIEF Questions 1-5 sum score ≥21).
7. Personal distress rated at least "moderate" on the Premature Ejaculation Profile (PEP) after the run-in period.
8. In good general health and medically stable as per investigator's judgment.
9. Willing to attempt intercourse at least 4 times during each 4-week treatment period.
10. For partners of childbearing potential: agreement to use acceptable contraception methods from Screening until 30 days post last dose.
11. Willing to avoid sperm donation from first dose until at least 90 days after the last dose.
12. Willing to limit alcohol intake on dosing days.
13. Ability to provide written informed consent and comply with study requirements.

Exclusion Criteria:

1. IELT >1 minute on more than 25% of attempts during the run-in period.
2. Fewer than 4 intercourse attempts during the run-in period.
3. Self-rated control of ejaculation as fair, good, or very good on the PEP.
4. Low personal distress ("not at all" or "a little bit") on the PEP.
5. Erectile dysfunction (IIEF Questions 1-5 sum score <21).
6. Significant anatomical penile deformities or history of penile surgery affecting erection.
7. History of other forms of sexual dysfunction.
8. Untreated or unstable thyroid dysfunction.
9. Recent use (within 4 weeks) of SSRIs, SNRIs, PDE5 inhibitors, MAO inhibitors, alpha blockers, 5-alpha reductase inhibitors, topical anesthetics, or tramadol.
10. History of sexual dysfunction treatments like Botox for PE in the past 6 months.
11. Active or uncontrolled sexually transmitted infections.
12. Severe psychiatric disorders, major depression, or suicidal ideation.
13. Clinically significant laboratory abnormalities or cardiovascular risk factors.
14. Positive drug screen (unless explained by prescription use).
15. Positive for HIV, Hepatitis B, or Hepatitis C.
16. Planned major surgery during study period.
17. BMI outside 18.0-35.0 kg/m² or weight <50 kg.