In clinical studies of sildenafil, some men are more likely to experience a placebo effect than others.
A recent Journal of Sexual Medicine study reports that race, age, and health status appear to be predictors of a placebo effect, although the authors recommended further research to determine why it happens.
Sildenafil (brand name: Viagra) is a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction (ED).
Researchers conducted a retrospective analysis of the placebo groups in 42 double-blind, placebo-controlled, flexible-dose sildenafil studies. Most of the studies were at least 12 weeks long. All used the International Index of Erectile Function (IIEF) Erectile Function Domain (EFD) as the main assessment tool.
Overall, 4,360 men participated in the placebo arms of their respective studies. About 14% of these men responded to placebo treatment with IIEF-EFD scores of 26 or above and were categorized as the normalization group. The rest of the men, whose IIEF-EFD scores were below 26, made up the non-responder group.
Across both groups, most of the men were between the ages of 45 and 65 and the majority were white. Rates of adverse events, which included headache, flushing, and dizziness, were similar in both groups. Side effects were considered mild.
After their analysis, the researchers determined that black men and men younger than age 45 were more likely to have a placebo response, along with men with mild ED and those who did not have diabetes. As the duration of ED increased, the likelihood of a placebo effect decreased.
More research is needed to determine why these results occurred, the authors said. Further investigation could help clinicians develop treatment protocols and determine best practices for clinical trials, the authors said.
“Of note, although response to placebo is not equivalent to response to no treatment, this extensive analysis overall demonstrates that sildenafil treatment has significantly greater effect than placebo. Clinicians should therefore initiate sildenafil treatment without concern about a placebo effect,” they added.
The Journal of Sexual Medicine
Mulhall, John P., MD, et al.
“Predictors of Erectile Function Normalization in Men With Erectile Dysfunction Treated With Placebo”
(Full-text. Published online: May 9, 2018)