Erectile Dysfunction Drug Tadalafil Exerts Modest Glucose Control

Mitchel L. Zoler, PhD, for Medscape

December 09, 2021

Key Takeaways

  • Six months of daily treatment with tadalafil (Cialis), an agent that treats erectile dysfunction (ED), in men with both ED and type 2 diabetes led to significant improvement in glucose control compared with placebo in a prospective, randomized study of 68 patients who completed the study.

  • Tadalafil was well-tolerated and no participants discontinued the study due to treatment-emergent adverse effects.

  • The study was conducted at a single center in South Korea.

  • The study is currently a preprint and has not been peer-reviewed.

Why This Matters

  • Low-dose tadalafil appeared effective and safe for both improving glucose control and erectile function in men with type 2 diabetes and erectile dysfunction.

  • Evidence shows that men with diabetes are over threefold more likely to have ED compared to men without diabetes.

  • Results from a prior study had shown that treatment of men with type 2 diabetes and ED with 5 mg oral tadalafil once daily is effective for improving ED and is safe and well tolerated. The new results show how this treatment affects glucose control.

Study Design

  • Researchers recruited eligible men from the outpatient clinic of Myongji Hospital, South Korea, during January 2017 and November 2018.

  • Enrolled men were 35- to 75-years-old with a diagnosis of type 2 diabetes and ED for more than 1 year.

  • Enrolled patients had a regular sexual partner and had had intercourse at least once during the prior month, but also had a history of persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance.

  • All enrolled patients had an A1c level of less than 9% and no history of treatment with a phosphodiesterase type 5 (PDE-5) inhibitor (the drug class that includes tadalafil) during the prior 3 months

  • Assessed outcomes included change from baseline in A1c, change in fasting plasma glucose, and changes in two measures of ED, the International Index of Erectile Function (IIEF-5) score and the International Prostate Symptom Score (IPSS).

  • The IIEF-5 score and IPSS at baseline did not differ between the two treatment groups.

  • Researchers randomized 50 patients to receive 5 mg oral tadalafil daily and 25 patients to receive placebo. After 6 months, 45 patients in the tadalafil group and 23 in the placebo group had completed the full treatment protocol and their 6-month assessment.

Key Results

  • At the end of the study, A1c levels declined compared with baseline by an average of 0.137% in the tadalafil group and rose by an average of 0.196% in the placebo group (P = .030).

  • After 6 months, average fasting plasma glucose was 6.40 mg/dL lower than baseline in the tadalafil group and was 5.35 mg/dL higher than baseline in the placebo group (P = .046).

  • Improvement in the IIEF-5 score was significantly greater in the tadalafil group than in the placebo group at 6 months, with an average score of 6.56 with tadalafil and 2.22 with placebo (P = .003).

  • The IPSS showed a numerical improvement among patients taking tadalafil compared with those taking placebo, which was not significant.


  • A relatively small, single-center study.

  • The analyses did not adjust for confounding variables that could affect the results, such as lifestyle modifications.

  • The possible mechanisms of the observed effects of tadalafil on glucose control are unclear. 

  • Larger, long-term, randomized controlled trials are needed to further document the hypothesized effects of tadalafil on glucose control.


  • The study was supported by Hanmi Pharmaceutical, a company that markets a formulation of tamsulosin and tadalafil (Gugutams), which is indicated for ED.

  • Hanmi Pharmaceutical had no role in the design, conduct, or analysis of the trial.

  • None of the authors had disclosures.

This is a summary of a preprint research study written by researchers at Myongji Hospital in Goyang, Korea, and at Hanyang University Medical Center in Seoul, Korea, on Research Square provided to you by Medscape. This study has not yet been peer-reviewed. The full text of the study can be found on

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