If you’re looking into using finasteride to treat male pattern baldness, you might be wondering how it will affect your testosterone levels. So, in this blog, we’re going to break down exactly what happens to hormone levels when using finasteride, and the potential side effects that can be linked to these changes.
How finasteride works
Finasteride prevents hair loss by blocking 5a-reductase, the enzyme that converts testosterone into dihyrdrotestosterone (DHT). Some men are more genetically sensitive to DHT, which binds to receptors on the hair follicle and affects the hair growth cycle. The anagen (growth) phase gets shorter, the hair follicle shrinks and stops producing thick, healthy hair which leads to gradual thinning.
By blocking type-1 of 5a-reductase, finasteride lowers DHT levels which has been shown in trials to stop further hair loss, promote hair growth and improve hair thickness.
How does it affect DHT and testosterone levels?
Research shows that using finasteride actually causes a slight increase in testosterone levels, because less is being converted into DHT, the hormone which causes male pattern baldness.
The standard finasteride dosage for treating male pattern hair loss is 1mg/day. Using this dose for 1 year reduced serum DHT levels (DHT levels in the blood) in men by a median 68%, and increased testosterone levels by 9%. This rise in testosterone was still in the normal range for men, so isn’t considered clinically significant.
Some guys who are knowledgeable on this subject might be wondering how the rise in testosterone impacts estradiol (belonging to group of female sex hormones, estrogen) levels. In men, estrogen is important for regulating various bodily functions like fat distribution, bone density and even regulating libido and erectile function. The balance of testosterone and estradiol is important though: a rise in testosterone might signal to the body to produce more estradiol, and vice versa, to keep the ratio in check.
Research shows that estradiol levels can rise alongside the increase in testosterone in men using 1mg finasteride daily, but the ratio of testosterone: estradiol is unaltered – which is why side effects linked to too high estradiol levels such as gynecomastia (breast tissue growth) are rare. In clinical trials on finasteride 1mg/day for hair loss, the incidence of breast tenderness and enlargement was the same as patients treated with placebo (0.4%).
What about sexual side effects?
Lots of guys think of testosterone when they link about sexual side effects like erectile dysfunction and loss of libido. In fact, DHT plays a more direct role in regulating sexual function in men, which is why finasteride can cause sexual side effects. But how common are they?
In clinical trials involving a total of 1,879 men, about 3.8% of men using finasteride reported sexual side effects compared to 2.1% in patients treated with placebo. However, in this trial the side effects generally resolved either during continued treatment or after stopping the drug.
So, men using a dummy treatment, aka placebo, also reported sexual side effects, so symptoms can occur even without finasteride use. This could indicate that the awareness of side effects can lead to more reports, a phenomenon known as the ‘nocebo effect’. A randomised controlled study looked into this in older men using 5mg finasteride to treat enlarged prostate: in the group told about potential side effect, reports were about 3 times as high as in the group which were not told about side effects.
However, the risk is still real. A meta-analysis in 2018 which analysed data from 15 placebo-controlled trials involving more than 4000 men concluded that the risk of sexual dysfunction was 1.66 times placebo. Trials show that the risk of sexual side effects is small but real, which is why finasteride comes with warnings. In most reports, symptoms go away with continued use or when the medication is stopped, but there have been a small number of reports of side effects persisting even after discontinuation.
If you think you might be experiencing side effects with finasteride use, it’s best to speak to your doctor for advice before continuing.
All of our blog articles are reviewed by our Medical Director before publication.
