Intervention: Tadalafil
Trial phase: Phase 4
ATC code: C02KX52 | C02KX54 | G04BE08 | G04CA54 | G04CB51
SMILES: [H][C@]12Cc3c([nH]c4ccccc34)[C@@H](c3ccc4c(c3)OCO4)N1C(=O)CN(C)C2=O
Sex: Male
Age groups: Adult | Older Adult
Healthy volunteers: Accepts Healthy Volunteers
Participants at risk: 118
Group description: No drug during baseline period followed by tadalafil 5 mg for 14 days.
Eligibility criteria:
Inclusion Criteria:

Male and at least 18 years old, with at least a 3-month history of erectile dysfunction (ED).
Anticipate having same adult female sexual partner during the study.
Agree to make at least 4 sexual intercourse attempts with the female partner during the 4-week run-in phase without medication.
Agree to make at least 1 sexual intercourse attempt per day with the female partner during days 1-4 following randomization (with a minimum of three attempts required during that period). Also agree to make at least 3 intercourse attempts during days 5-14 following randomization.
Agree not to use any other ED treatment during the study and for 24 hours after the final study visit.

Partner Inclusion Criteria:

Female and at least 18 years old.
Agree to make at least 4 sexual intercourse attempts with the male sexual study partner during the 4-week run-in phase without medication.
Agree to make at least 1 sexual intercourse attempt per day with the male partner during days 1-4 following randomization
Agree to make at least 3 intercourse attempts during days 5-14 following randomization.

Exclusion Criteria:

Previous or current treatment with tadalafil or any phosphodiesterase type 5 (PDE5) inhibitor on a daily basis for once daily use.
ED caused by other primary sexual disorders, or untreated or inadequately treated endocrine disease.
History of radical prostatectomy, other pelvic surgery or penile implant.
Clinically significant penile deformity in the opinion of the investigator.
Clinically significant renal insufficiency, or hepatobiliary disease as determined by the investigator.
Glycosylated hemoglobin of >11%.
Present with chronic stable angina treated with long-acting nitrates, or with chronic stable angina requiring short-acting nitrates in the last 90 days, or with angina occurring during sexual intercourse in the last 6 months.
Have any significant cardiac conditions as described in the protocol exclusion criteria.
Have a history of significant central nervous system injuries within the last 6 months.
Have a history of Human Immunodeficiency Virus infection.
Have any condition that would interfere with the subject's ability to provide informed consent or comply with study instructions, would place subject at increased risk, or might confound the interpretation of the study results.
Currently receive treatment with nitrates, cancer chemotherapy, or antiandrogens (except finasteride taken as Propecia or Proscar, or Avodart [dutasteride]).
History of drug, alcohol, or substance abuse within the past 6 months, as assessed by the investigator.
Previously completed or withdrawn from any other study investigating tadalafil for once daily use.
Received treatment within the last 30 days with a drug that has not received regulatory approval for any indication at the time of study entry.
Prior ineffective treatment with any PDE5 inhibitor in the opinion of the investigator.