A user review of finasteride on Drugs.com describes a disturbing symptom: “This drug literally caused my genitals to go permanently numb at 29 years old. Chemical castration in a bottle.” Another reviewer said “my penis is completely numb… The ‘side effects’ also appear to NOT be reversible.” Genital numbness is also among the most common symptoms reported to the U.S. Food and Drug Administration for men aged 18–40 who took finasteride.
Genital numbness is a symptom, but medicine is interested in signs, meaning characteristics which can be observed and measured. A cough is a symptom, while a lab test showing a respiratory virus is a sign. Signs are important for diagnosis, and often carry more weight than symptoms. Some doctors are skeptical that a disease is real until they can observe signs.
The syndrome that may follow use of finasteride, dutasteride or saw palmetto has many possible symptoms but few signs as of now (these drugs are known as 5-alpha reductase inhibitors, or 5ARIs). Many physicians therefore see the syndrome as a made-up disease claimed by men suffering from depression or ‘Internet illness.’ They say that low libido is a known symptom of depression. While this may be true in some cases, genital numbness is not a symptom of depression. Therefore, a medical sign of genital numbness could differentiate the condition from depression. There are tests for the symptom, but they are not well-known or widely available.1–3 (Even if a sign of numbness were found, the post-5ARI syndrome could not be officially diagnosed, as it is not recognized by a medical authority. Still, the search for signs will help to define the disease.)
There appears to be only one study and one conference abstract aiming to measure genital numbness in men with lasting dysfunctions after using 5ARIs. This post reviews the findings, then provides an overview of medical tests for genital numbness and other disorders of the penis.
Response to electrical stimulus
This study is from the lab of Dr. Roberto Cosimo Melcangi who has overseen a longstanding research program on post-finasteride syndrome. The study group consisted of 16 male post-finasteride patients. Nerve responses in the penis were assessed using a method called somatosensory evoked potentials. An electrical signal was transmitted between ring electrodes at both ends of the penis and recorded. In three of 16 patients, no response was detected, while in a fourth patient, the response was delayed by more than 45 milliseconds. No abnormal findings were reported for the other 12 patients.
Separately, patients filled out a questionnaire reporting how often they experienced various symptoms, including genital numbness. Patients answered as follows: Never: 2 patients; Sometimes: 4; Often: 3; Always: 7. Therefore, ten patients (63%) reported they felt numbness often or always, yet only four (25%) had abnormal results in the evoked potentials test. It is not clear why the test and the questionnaire are inconsistent. This is an example of how a symptom cannot always be observed as a sign.
Quantitative sensory testing
Carlisle M, Uloko M, Yee A, Goldstein S, Goldstein I. Vascular, neurologic and hormonal abnormalities in men with persistent sexual dysfunction after discontinuation of finasteride. J Urol. 2022. DOI • Poster (PDF)
This abstract was submitted to the 2022 annual meeting of the American Urological Association. The authors were affiliated with San Diego Sexual Medicine. One was Dr. Irwin Goldstein, the clinic’s founder and a past President of the Sexual Medicine Society of North America. Dr. Goldstein published the third paper on persistent symptoms of 5ARIs, which appeared in 2011.
The poster summarized charts of 96 male patients seen at SDSM from 2015–2020 who had persistent sexual complaints after stopping finasteride. Patients who had sexual dysfunction prior to using finasteride and those who had used SSRI antidepressants while taking finasteride were excluded. The abstract summarized results of quantitative sensory testing (QST). This technique measures sensitivity to different kinds of stimulus such as vibration, pressure, location, warmth or coldness (though the measures used in this case series were not reported).1 The abstract reported that 83% of post-finasteride patients had abnormal results of QST.
Overview of techniques
This study was not specifically about post-5ARI syndrome, but lists a number of tests that could be considered for diagnosis of numbness and other penile abnormalities.
Tests of sensitivity and responsiveness
|What it measures
|Quantitative Sensory Testing (QST)
|Penile sensitivity to vibration, pressure, location, and warmth or coldness.1,2 Measurement of vibration is called biothesiometry.
|Dorsal nerve conduction velocity
|Speed of signal in the penile dorsal nerve
|Dorsal nerve somatosensory-evoked potential
|Intensity and other attributes of nerve signal in the penile dorsal nerve
|Responsiveness of a muscle in the perineum, an area between the anus and genitals
Tests of structure and function
|What it measures
|Penile Doppler ultrasonography
|Visualization of disease processes including including Peyronie’s disease, penile fractures and tumors4
|Hardness and fullness of nighttime erections5,6
|Venous leak and arterial insufficiency7
|Visualization of abnormalities in cavernous tissues7
These tests could be of interest to post-5ARI patients seeking diagnostic signs, as well as researchers studying lasting dysfunctions after use of 5ARIs.
- Bleustein CB, Eckholdt H, Arezzo JC, Melman A. Quantitative somatosensory testing of the penis: optimizing the clinical neurological examination. J Urol. 2003. doi:10.1097/01.ju.0000065824.35996.c8 • PubMed
- Wiggins A, Farrell MR, Tsambarlis P, Levine LA. The penile sensitivity ratio: a novel application of biothesiometry to assess changes in penile sensitivity. J Sex Med. 2019. doi:10.1016/j.jsxm.2019.01.002 • PubMed
- Shafik A, Ahmed I, El Sibai O, Shafik AA. The hypoactive corpora cavernosa with degenerative erectile dysfunction: a new syndrome. BMC Urol. 2006. doi:10.1186/1471-2490-6-13 • PubMed • PMC full text
- Aversa A, Crafa A, Greco EA, Chiefari E, Brunetti A, La Vignera S. The penile duplex ultrasound: How and when to perform it? Andrology. 2021. doi:10.1111/andr.13029 • PubMed
- Elhanbly S, Elkholy A, Elbayomy Y, Elsaid M, Abdel-gaber S. Nocturnal penile erections: the diagnostic value of tumescence and rigidity activity units. Int J Impot Res. 2009. doi:10.1038/ijir.2009.49 • PubMed
- RigiScan PLUS: Rigidity Assessment System. GOTOP Medical. Accessed July 19, 2023.
- Chung E. Contemporary and novel imaging studies for the evaluation of erectile dysfunction. Med Sci (Basel). 2019. doi:10.3390/medsci7080087 • PubMed • PMC full text
- Carlisle M, Uloko M, Yee A, Goldstein S, Goldstein I. Vascular, neurologic and hormonal abnormalities in men with persistent sexual dysfunction after discontinuation of finasteride. J Urol. 2022 May 1;207(5S):e620–621. doi:10.1097/JU.0000000000002592.07 • Poster (PDF)