How does Finasteride Impact Testosterone and Estrogen Levels?

Ever since I first started taking Finasteride a decade ago (with several stops and restarts in between), I have always been wary of side effects.  I therefore decided to be cautious and take around half the recommend dose (i.e., 1.25 mg once every two days instead of 1 mg every day).  There are numerous people who take 5 mg (!) of Finasteride per day for enlarged prostates and they generally seem to get limited to no side effects based on various studies, so perhaps I am overly cautious.  At the same time, there are also many hair loss sufferers who have taken 1 mg per day and complain about persistent side effects even after stopping the medication. However, as a percent of all people who take Finasteride, this number is tiny. Nevertheless, it still makes me err on the side of caution.  Recently, I tried to find out exactly how Finasteride impacts estrogen and testosterone levels in men.

Finasteride and Estrogen

Finasteride raises estrogen (the female hormone) levels, and this tends to be the number one concern of people taking the drug. Higher levels of estrogen in men can result in feminizing effects such as gynecomastia and increased body fat levels, along with sexual problems.  For years, I was curious as to how much estrogen levels go up by in men who are on Finasteride.  Do they go up to levels found in women (that would be scary)?  What are the typical estrogen levels in men and in women? After spending a good amount of time, I finally found an official brochure from the manufacturer of Propecia, Merck, that states that “mean circulating levels of testosterone and estradiol were increased by approximately 15%“. Estradiol = Estrogen (see next paragraph).  However, now I needed to find out how that compares to estrogen levels found in women.

There are three types of naturally occurring estrogens in women: estrone (E1), estradiol (E2) and estriol (E3).  Estradiol is the most important estrogen in non-pregnant females prior to menopause, estriol is the most important one in pregnant females, and estrone if the most important one after menopause.  Estradiol is the most potent of these three estrogens.

Blood tests for estrogen generally look at estradiol levels.  Men’s estradiol levels range from 15-60 pg/ml over the course of their lifetimes.  For women, the range varies significantly throughout their life, including during each menstrual cycle.  A female’s lifetime estradiol range is from 20-400 pg/ml, with post-menopausal levels being similar to those in men.  Various sources I checked show slightly different estimates for the above ranges, but in general, women have significantly more estradiol then men prior to menopause.  It should be noted that while women’s estrogen levels are primarily manufactured by the ovaries, men’s levels are attained via the aromatase reaction that converts testosterone to estrogen.

From the above numbers, one can deduce that in young adult males, Finasteride will result in estradiol levels rising from say around 35 pg/ml to around 40 pg/ml (i.e., 15 percent increase).  This finding makes me a bit more comfortable in continuing to take Finasteride.  I also vaguely remember taking a blood test in the past in which one of the measurements was for prolactin, and my levels were normal despite my taking Finasteride 1.25 mg every two days at the time. Abnormal levels of prolactin indicate that something is wrong with your testosterone and/or estrogen levels (for both men and women).

Finasteride and Testosterone

Finasteride reduces the conversion of testosterone to dihydrotestosterone (DHT), resulting in higher levels of circulating testosterone.  According to the earlier mentioned Merck brochure on Propecia, Finasteride also increases circulating testosterone levels by 15%.  Considering that men start to lose testosterone levels starting in their 20s, this is perhaps not such a bad thing.  In fact an increasing number of older people take testosterone supplementation, and the most famous example is the incredible 77 year old Dr. Jeffry Life.  I am very surprised that this man is still alive despite injecting himself with testosterone at a relatively old age. Also see Dr. Life’s before and after photos.

Note that testosterone supplementation is a very controversial subject, and I would not try it.  High levels of testosterone are linked to death from heart attacks.  I also think I am getting more adult acne due to taking Finasteride, although I am not 100 percent certain about that.  Many hair loss forum members have wondered if the slight increase in testosterone when on Finasteride helps one gain a bit more muscle mass when working out.  Also see this page for ranges on average and free testosterone levels in men and women.

Testosterone to Estrogen Ratio

While the 15 percent rise in circulating testosterone and estrogen levels in men taking Finasteride 1mg per day does not seem much to me, it is important to also watch out for the testosterone to estrogen ratio in case you ever get blood tests done.  It is quite possible that some people will see a significantly higher increase in circulating testosterone than in circulating estrogen (or vice versa) when on Finasteride, and the change in this ratio can have a big impact on your side effects.  Various reports suggest that when the testosterone to estrogen ratio changes significantly, one can often get unexpected side effects.


Numerous reports I have read seem to suggest that women’s higher levels of estrogens protect them to some extent from various serious medical problems such as heart disease.  While higher estrogen levels in women also mean substantially higher rates of breast cancer in comparison to men, in general, estrogen has more pros than cons for women, and is one of the main reasons that women live around five years longer then men on average.

Many hair loss forum members (and body builders too) take an aromatase-inhibiting prescription drug called Arimidex that prevents estrogen levels from rising when on Finasteride.  I would never add yet another drug to my life considering how much I hate taking just one at the moment, but Arimidex seems to be a fairly popular and safe drug as far as I can tell.

8 thoughts on “How does Finasteride Impact Testosterone and Estrogen Levels?”

  1. There u go u, as you can see no problems!! Stop being afraid and take finasteride, has been keeping my hair since 18 and I’m 25, never had side effects.

  2. I’ve got mild Gyno after 1 week on 1.25 fin ED.

    I was taking fin for 2 month and stopped 10 days ago.
    When my hormones will stabilize? Will my gyno go away? It’s not noticeable but I feel it under my nipples.

  3. Great post thanks man…. Once you get past the scaremongering about fin and look at the stats out there , it does seem like its worth a shot if you know just how badly losing your hair will affect your self esteem. I haven’t started on it yet but it really think I will give it a try. Think i’ll get my blood work done first just to be safe and see how my hormones change later on! Also going to start on 0.5 mg to see how body treats it! Keep up the work dude all posts appreciated

    1. Thanks. The only other big issue is whether reducing DHT by so much has any harmful effects in the long run. A recent 10-year study did not find any long-term problems and I look forward to more such long-terms findings being published in the next several years. Finasteride was approved for treating BPH in 1992 and for treating hair loss in 1997, so we might get 15-20 year studies pretty soon.

  4. ADMIN this is a study report saying that finasteride does not cause undesirable sexual side effects.
    J Androl. 2008 Sep-Oct;29(5):514-23. doi: 10.2164/jandrol.108.005025. Epub 2008 Apr 17.
    The effect of 5 alpha-reductase inhibitors on erectile function.
    Canguven O1, Burnett AL.
    Author information
    The 5 alpha-reductase inhibitors, which inhibit conversion of testosterone to dihydrotestosterone, are used for miscellaneous clinical applications, including the treatment of benign prostatic hyperplasia and male pattern hair loss, and for possible reduction of the risk of prostate cancer. Erectile dysfunction has been associated with 5 alpha-reductase inhibitors. Overall, reports in the literature suggest rates of erectile dysfunction to be between 0.8%-33% in men using these medications. However, randomized controlled studies report the rates of erectile dysfunction to be between 0.8%-15.8%. The possible risk association is that these medications impact androgen function, which is understood to contribute to normal erectile physiology. The 5 alpha-reductase inhibitors result in a drop in median serum dihydrotestosterone levels by 60%-93% within 2 years, but there is no major change in testosterone levels. In this review, we surveyed studies on erectile dysfunction in patients treated with 5 alpha-reductase inhibitors and critically examined the evidence that associates 5 alpha-reductase inhibitors and erectile dysfunction. We conclude that 5 alpha-reductase inhibitors do not lead to erectile dysfunction to a significant degree, and we support the position that dihydrotestosterone is less relevant than testosterone in erectile function.

  5. There’s a much bigger problem about finasteride than any of the above: try Googling for articles on finasteride and Alzheimer’s.

  6. Also, finasteride works by blocking the conversion of testosterone to dihydrotrstosterone — but unfortunately it also interferes with the natural conversion of progesterone (via dihydroprogesterone) to alopregnanolone. (The alpha-II redustase enzyme which finasteride suppresses is essential to both of those conversions). Allopregnanolone is an important neurotransmitter necessary for proper maintenance of the myelin sheaths which protect neurons in the brain and spine, and a deficiency of it can therefore result in neurological diseases of “demyelination” — e.g. Parkinson’s disease and multiple sclerosis.

    Increasing your risk of Parkinson’s, multiple sclerosis and perhaps even Alzheimer’s disease in order to preserve a youthful-looking head of hair is not a cool idea. You mess around with your body’s natural hormonal and neurological system at your extreme peril.

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