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.
Finally, make sure to read my post on dutasteride (Avodart) and finasteride (Propecia) dosage discussion. Some of the reader comments in there are also very useful.