Category Archives: Estradiol

How Does Finasteride Impact Testosterone and Estrogen?

Ever since I first started taking Finasteride a decade ago, 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 Finasteride once every two days instead of 1 mg every day. I did not take the more expensive brand name Propecia.

Some people prefer natural DHT blockers. Although these are far less effective than Finasteride, they are usually side effect free. I am aware that there are numerous people who take 5 mg of Finasteride (Proscar) per day for enlarged prostates. They generally seem to get limited to no side effects based on various studies, so perhaps I am overly cautious.

Edit: I now take the much stronger Dutasteride to treat my hair loss.

Finasteride Chemical Structure
Finasteride Chemical Structure.

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 (aka the female hormone) levels. This tends to be the number one concern of people taking the drug when it comes to side effects. Higher levels of estrogen (oestrogen) in men can result in feminizing effects. These include gynecomastia (enlarged breasts in men), increased body fat levels and 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 my answer in an official brochure from the manufacturer of Propecia, Merck.

In there, it states the following: “mean circulating levels of testosterone and estradiol were increased by approximately 15%“. Estradiol is essentially the same as Estrogen (see next paragraph). However, now I needed to find out how estrogen levels in men that go up by 15% compare to levels in women.

Types of Estrogen

There are three types of naturally occurring estrogens in women:

  • Estrone (E1).
  • Estradiol (E2).
  • 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.

Update: A 2019 study from the US concluded that 5α-Reductase Inhibitor therapy is not associated with consistent and significant increases in serum testosterone levels.

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. However,  higher estrogen levels in women also mean substantially higher rates of breast cancer in comparison to men. Ultimately, the pros outweigh the cons. Low testosterone and high estrogen are among the main reasons that women outlive men by around five years on average.

Many hair loss forum members (and body builders too) take an aromatase-inhibiting prescription drug called Arimidex. It supposedly 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. Arimidex does seem to be a fairly popular and safe drug as far as I can tell. It is still best to consult your doctor or dermatologist first before taking such drugs.

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.

Estrogen Therapy and Hair Growth

For the male readers of this blog, estrogen (also known as oestrogen) is not something that one would consider to be of interest. For one, estrogen is a female hormone. What male in his right mind would want to start taking estrogen and get female secondary sexual characteristics?

Having said that, estrogen does have some beneficial properties for the heart. It is also though to be one of the main reasons behind why females outlive males. However, I would still pass on supplementing with the hormone.

Estrogen Hormone Therapy and Hair Growth

The reason I decided to write a post on estrogen is because I recently read an extremely interesting 2012 interview with Dr. George Cotsarelis. While the main part of the interview is devoted to the oft discussed PGD2, there are several other interesting subjects discussed. The second page of the interview is what really surprised me in a good way.

In the first part of this interview, Dr. Cotsarelis discusses the old and well known Dr. James Hamilton study from the 1950s. In this research, it was found that men who were castrated before puberty (eunuchs) never went bald. However, upon being given testosterone, those with a family history of baldness still started to loose hair.

The second part of the interview is more interesting. It covers the fact that even after someone has lost much of his hair due to androgenic alopecia, he can regrow a lot of it when given estrogen (after castration)!

This point is supposedly verified by many studies on Male-to-Female (MTF) transitioning transgender persons. Such patients show hair regrowth after their being castrated and getting on estrogen hormone replacement therapy (HRT). Usually with the addition of an anti-androgen such as Spironolactone.

While I do not think any of us men want to get castrated or take estrogen (estradiol), this is still an incredible finding. One of the best examples is in the before and after image below from this study.

Estrogen Treatment Hair Growth
Estrogen (Estradiol) Treatment Hair Regrowth. Source: Journal of the American Academy of Dermatology.

Note that both estrogen and progesterone extend the anagen growth phase cycle of hair follicles. In contrast, testosterone and dihydrotestosterone (DHT) do the opposite and shorter the hair growth phase. Make sure to also read my post on how finasteride impacts testosterone and estrogen levels.

Hair Regrowth Difficulties

Over the years, I have read a number of articles in which doctors and professionals seem to suggest that once hair is gone (turns vellus), it can never return. This is also why Finasteride and Minoxidil virtually never bring back any significant amount of hair for someone who is mostly or entirely bald. However, it seems like hair can regrow in fully bald areas of the scalp in some instances.

There have been anecdotal reviews on Dutasteride actually regrowing long disappeared hair. But these have been few and far between. Over a decade ago, Dr. Marty Sawaya caused an insane level of excitement on hair loss forums when she reported that one of her older patients gained back most of his lost hair when on Dutasteride. But that whole episode was controversial and not replicated.

More recent research suggests that a balding scalp still has all the follicle stem cells intact. But certain progenitor cells have become depleted. Basically, the cells are there, but the activity is not there. Dr. Cotsarelis has suggested that perhaps blocking PGD2 will allow the stem cells to make progenitor cells again. However, this is not a certainty, and neither is hair regrowth guaranteed once PGD2 is inhibited.

I suspect that this powerful impact of estrogen on hair regrowth is still not strong enough to grow back all of one’s lost hair. This is because many older balding MTF transsexuals seem to get hair transplants even after getting castrated and beginning estrogen therapy.

Finally, for men who take Finasteride (brand names Propecia, Proscar, Finpecia), one potential side effect is increased estrogen levels. This sometimes results in the dreaded gynecomastia (male breast enlargement), along with fat gain in other parts of the body. Their are numerous complaints on hair loss forums about this side effect.