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LibraryHair Loss TreatmentsIs Post-Finasteride Syndrome Real?
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Is post-finasteride syndrome real?

Written by
XYON Medical Team
Clinically reviewed by
Dr. C. Han, MD, FRCPC
Dr. S. Pimstone, MD, PhD, FRCPC
Dr. V. Hasson, MD

What is post-finasteride syndrome?

Experts disagree about whether post-finasteride syndrome is a real condition. Since it was first approved for the treatment of male pattern hair loss in 1997, oral finasteride and its side effects have been extensively researched.

Finasteride is generally safe and well-tolerated, but reported adverse effects include impaired sexual function, gynecomastia (breast enlargement) and depression. In some individuals, side effects following treatment with finasteride persist even after stopping the medication. This is referred to as post-finasteride syndrome (PFS).

Currently, it is unclear what the incidence and clinical outcomes are of individuals with PFS. However, it is important to take concerns about PFS seriously, as the syndrome can have a significant impact on quality of life.

This article goes into detail about the possible biological mechanisms behind mood changes and sexual side effects associated with finasteride use and whether these effects are truly permanent. We also discuss possible reasons for why data on post-finasteride syndrome is so controversial.

Finasteride and the brain

Study data suggests that finasteride may be linked to neurological side effects. When the medication is taken orally and enters the systemic circulation, there is a risk that the medication may have an impact on tissues other than hair follicles. In this case, the brain is potentially affected..

Some hormones specifically impact brain function. These hormones are called neuroactive steroids, which have been studied in connection with mood changes in finasteride users (Diviccaro et al., 2020).

Neuroactive steroids cannot be produced without the 5-alpha reductase enzyme. When finasteride is taken via the oral route, the blocking action of the medication may also reduce levels of these important regulatory hormones.

Under normal circumstances, these hormones alter the response of brain cells to chemical compounds called neurotransmitters that convey nerve signals within the brain and between the brain and rest of the body. It’s possible that changes to levels of these hormones may have something to do with the pathophysiology and treatment of affective and anxiety disorders (Römer & Gass, 2010).

Are these neurological changes permanent?
Additional research is needed, but preliminary data suggests that the answer is no. One study has shown that directly supplementing neuroactive steroids can lead to an improvement in mood, lending support to the reversibility of symptoms (Sripada et al., 2013).

Ok. But does finasteride permanently lower sex drive?
Again, there appears to be a lack of conclusive evidence but the answer is probably no. Testosterone is the male sex steroid hormone most often associated with sex drive but some researchers speculate that DHT (which finasteride lowers) may also have a role in sexual motivation.

The relationship between DHT and sex drive was explored in a 2016 study that focused on identifying common characteristics of men who reported PFS. Brain imaging studies of participants who were shown erotic imagery revealed abnormal activity in regions of the brain involved in sexual arousal and motivation (Basaria et al., 2016).

However, despite noting this unusual response to erotic stimuli, researchers were not able to conclude whether finasteride use actually caused these symptoms. Of note, the men in this study did not demonstrate any prior evidence of hormonal or enzyme abnormalities and once participants stopped taking finasteride, brain function seemed to return to normal (Basaria et al., 2016).

Finasteride: sexual side effects

Before diving into whether sexual side effects associated with finasteride are permanent, let’s consider the body’s response to the medication.

In clinical trials of 5-alpha reductase inhibitors such as finasteride and dutasteride, the incidence of erectile dysfunction ranged from 6-8% (Traish et al., 2011). Researchers theorize that finasteride may indirectly affect sexual function by reducing androgen levels.

Androgens are involved in physiological processes necessary for proper erectile function. Two of these processes are (1) nitric oxide gas production and (2) smooth muscle relaxation.

Androgens and erectile dysfunction
Blood vessels are made up of several layers of tissue. One of these layers consists of smooth muscle. In contrast to skeletal muscle, which is associated with body parts that are voluntarily moved such as the biceps and quadriceps, smooth muscle is involuntarily controlled by the nervous system.

Smooth muscle facilitates constriction and dilation of blood vessels in response to sensory input (Hafen & Burns, 2020). Normal erectile function requires smooth muscles of the penis to relax in order to maximize blood flow to the corpora cavernosum, one of three types of special erectile tissues.

This relaxation requires a blood vessel dilating gas called nitric oxide. Nitric oxide is produced by the nerves and lining of the corpus cavernosum. It triggers a chain of reactions that ends with the local dilation of blood vessels (Burnett, 2004).

Like most other biologically significant molecules, nitric oxide is made with the help of an enzyme. The specific enzyme in this case is called nitric oxide synthase.

Prior research has shown that local levels of this enzyme in the corpus cavernosum depend on androgens. A decrease in androgens may reduce the production of nitric oxide and vascular dilation. This could have a detrimental effect on erectile function (Canguven & Burnett, 2013).

In 2003, a study also found a link between decreased androgen levels and changes in penile tissue composition. These changes negatively affected the ability to achieve and maintain erection and were associated with the replacement of normal erectile tissue with fibrous tissue incapable of expanding (Traish et al., 2003).

Finasteride and reduced ejaculatory volume
Some individuals with PFS have reported decreased ejaculatory volume. In 2008, a study was conducted on the effects of finasteride and dutasteride on sexual function in young men over a period of 52 weeks (Amory et al., 2008).

Researchers found that participants experienced slight decreases in ejaculatory volume during treatment. However, these changes were usually temporary and did not have serious effects on sexual function or satisfaction overall (Amory et al., 2008).

Are these sexual side effects permanent?
It’s unclear, but the duration of treatment could play a role. When it comes to changes in tissue composition that may affect the ability to achieve an erection, one animal study showed that the severity of erectile dysfunction associated with 5-alpha reductase inhibitor use was partially dependent on the duration of treatment (Sung et al., 2019).

Stopping the medication at the first signs of symptoms could mean better recovery of function. And while the same study cites instances of permanent erectile dysfunction, this risk does not appear to outweigh the potential benefits of responsible dosing and treatment duration.

Should I be worried about post-finasteride syndrome?

Although finasteride is generally a safe treatment for male pattern hair loss, we understand that the contradictory data on PFS can be overwhelming. As it stands, there is no conclusive data linking finasteride use to permanent side effects.

However, there are two factors that may help explain the inconsistencies in research data on PFS: the nocebo effect and the existence of other medical conditions that may increase one’s risk of having adverse effects.

It’s also worth noting that some studies may not be appropriately designed to capture side effect information.

Volunteer bias and the nocebo effect
Volunteer bias and the nocebo effect may influence PFS data. Volunteer bias, also known as self-selection bias, is a phenomenon when participants who agree to take part in a study have a clinical status that differs from non-participants (Tripepi et al., 2010).

This is the case when participants are recruited from websites or forums that focus on the side effects of finasteride. These individuals already identify with symptoms (Fertig et al., 2017).

Meanwhile, the nocebo effect applies when prior knowledge of possible side effects leads to a negative response to an otherwise safe or well-tolerated therapy (Colloca & Miller, 2011).

This effect was observed in a 2007 study that examined the impact of counselling on sexual side effect rates in finasteride users (Mondaini et al., 2007). 43.6% of individuals who were counselled about possible risks went on to report symptoms, compared to only 15.3% of those who were not (Pereira & Coelho, 2020).

A study of persistent (≥3 months) sexual side effects following the use of 1 mg oral finasteride daily found that 94% of participants reported low libido, 92% experienced erectile dysfunction and 92% had problems with arousal (Irwig & Kolukula, 2011). However these results are confounded by data from other placebo-controlled studies.

Take for example a 2003 study, which compared 5 mg oral finasteride daily to placebo for the treatment of benign prostatic hyperplasia. Researchers found that among participants who withdrew after initial symptoms of sexual dysfunction, members of the placebo group actually reported more persistent side effects (Pereira & Coelho, 2020).

Medical history and individual side effect risk
When assessing the risk of long-term psychiatric changes and/or depression associated with finasteride use, individual predisposition to mood disorders is a factor.

This was observed in a trial conducted by Ganzer and Jacobs in 2018 that assessed the anxiety and depression risk of a group of finasteride users. They found that 55% of study participants had a pre-existing diagnosis of a mood disorder and 28% had a family history of mental illness (Ganzer & Jacobs, 2018).

However, a separate study found that depressive symptoms and suicidal ideation were far more likely in former oral finasteride users than a control group that had never been exposed to the medication (Irwig, 2012). Given these conflicting findings, it is not possible to say whether finasteride directly causes psychiatric changes in some individuals.

The takeaway

Post-finasteride syndrome may, or may not exist. More rigorous studies are needed to establish a connection between finasteride use and long term side effects.

The clinical data suggests that finasteride may be associated with an increased risk of sexual (and to a lesser extent, neurological) side effects in a subset of individuals. But risks can be mitigated by ensuring that your physician is aware of your medical history and any specific concerns you may have prior to starting treatment.

Bear in mind that existing research on PFS has largely focused on the oral form of the medication. Compounded forms of finasteride such as Topical Finasteride, with SiloxysSystem™ Gel may be an option for those concerned about side effects. This treatment is a compounded medication which is only available with a prescription, so we recommend talking to a physician to determine if this hair loss solution is appropriate for you.

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