Estrogen Blockers: Everything You Need To Know

Estrogen Blockers

If you’re reading this article, it’s probably because you’re considering taking an Estrogen blocker of some kind.

Whether it’s a supplement or a drug, there are a few things you should probably understand before mindlessly ingesting these types of substances.

The truth is, most Estrogen blockers are a complete waste of money for 2 reasons:

  1. They don’t actually block estrogen
  2. Blocking estrogen won’t help you build the body you want

While it is true that there are some practical uses for Estrogen blockers, most people won’t benefit from using them to any sort of noticeable degree.

Especially when it comes to fitness.  In fact, you need a certain amount of Estrogen to build muscle effectively, but more on that later…

The point is that before you go messing with your hormones, you should at least come to a complete understanding of how everything works.

In this article, we’ll go over everything you need to know about Estrogen blockers, including:

  • What Is Estrogen?
  • What Does It Do?
  • Why Is It So Bad? (It’s Not)
  • How Do Estrogen Blockers Work?
  • Which Ones Work And Which Ones Don’t?
  • Where To Buy Estrogen Blockers That Do Work
  • Estrogen Blocker Side Effects

And a whole lot more useful information…

So, if you’re ready to dive into the wonderful world of exaggerated claims and pseudo-science that is Estrogen blockers, let’s start from the top!

What Is Estrogen?

Estrogen Molecule

Estrogen is the primary female sex hormone (chemical messenger) which is primarily responsible for promoting physiological female characteristics.

It’s heavily involved in various physiological functions including puberty and the menstrual cycle.

But it’s not just a female hormone.  Both Estrogen and Testosterone exist in men AND women.

It’s just that men have higher Testosterone levels and lower Estrogen levels, while women have higher Estrogen levels and lower Testosterone levels.

We’re talking about two of the most important chemicals in the body.  These chemicals literally dictate who we are and how we act, not to mention having a massive impact on a various other bodily functions.

In females, Estrogen is produced mostly in the ovaries, but in males it’s also produced in the testes where it plays a vital role in spermatogenesis and steroidogenesis.

Although we often refer to Estrogen as a single chemical, there are actually a few distinct types.  The 3 most common are:

  • Estradiol
  • Estrone
  • Estriol

Out of these three, Estradiol is considered the strongest in terms of estrogenic effects.  Estrone and Estriol are much weaker, so for all intents and purposes, when use the term “Estrogen”, we’re pretty much just referring to Estradiol.

Estradiol is the primary cuplrit behind many of the negative effects of Estrogen.  The same negative effects that make people want to reach for Estrogen blockers.

When Estrogen is secreted and released into the body, it binds to Estrogen Receptors located in specific tissues.  Only certain tissues have Estrogen Receptors which means it only impacts certain parts of the the body.

This actually explains why high Estrogen levels can result in gynecomastia.  That is, enlargement of male breast tissue, more commonly known as “bitch tits”.

Of course, because Estrogen plays such as pivotal role to begin with, it impacts at on of other body functions as well.  So any kind of imbalance can be untold consequences.

What Does Estrogen Do?

What Does Estrogen Do?

In women, Estrogen is responsible for things like ovulation and puberty, but what about men?

Do we really need it?  Sure we do…

In men, Estrogen is heavily involved in:

Just to name a few real quick…

So before you go thinking you want to do away with Estrogen altogether, keep in mind that even as men, it’s imperative that we have SOME estrogen.

That said, higher than normal Estrogen levels can have a nasty impact on general manliness, so it makes sense that so many men would reach for an estrogen blockers.

Especially since most companies that sell them promote them as muscle builders, despite research which clearly shows suppressing Estrogen does not:

  • increase Testosterone by much
  • favorably influence body composition

In order to understand why though that is, we need to talk about what’s actually going on inside your body when you  take an Estrogen blocker (that actually works).

What Are Estrogen Blockers?

What Are Estrogen Blockers?

The term Estrogen blocker refers to any drug or substance that–you guessed it–blocks Estrogen!  At least, anything that blocks Estrogenic effects.

There are a couple ways to reduce the effects of Estrogen that don’t technically involve reducing the amount you secrete, but we’ll get into that shortly…

The most common Estrogen blocking drugs are:

  • Femara (Letrozole)
  • Nolvadex (Tamoxifen)
  • Clomid (Clomiphene)
  • Arimidex (Anastrozole)
  • Aromasin (Exemestane)

There are plenty of other drugs that block Estrogen as well as a seemingly infinite number of supplements that claim to do so as well.

Nolvadex, or Tamoxifen Citrate (it’s generic name), is by far the most popular, in terms of sales, grossing the company that first introduced it–AstraZeneca– just over 1 billion dollars in 2001 alone.

That’s what you called a ‘blockbuster drug’, although now the patent has warn off and it’s sold all over the place by a ton of different companies and individuals.


Because it really is effective at suppressing Estrogen.  These drugs actually work, and they work well.

How Do Estrogen Blockers Work?

How Do Estrogen Blockers Work?

There are 2 primary ways that Estrogen blockers block Estrogen…

One way is to use a molecule that resembles Estrogen so closely that it can actually bind to Estrogen receptors, preventing actual Estrogen from doing so.  If Estrogen can’t bind to it’s receptors, it remains inactive.

In other words, it can’t do anything or cause any estrogen-like effects.

Substances that work this way are called Selective Estrogen Receptor Modulators, or SERMs.

The most commonly used SERMs are:

  • Tamoxifen (Nolvadex)
  • Clomiphene (Clomid)

Out of these, Nolvadex is the most popular.  They’ve all been proven to work, but Nolvadex easily the most powerful and has some other unique properties as well that make it superior in some ways.

The way to think about SERMs is this:

If Estrogen is a key and the Estrogen receptor is the lock, SERMs are substances that are so similar to Estrogen that they can fit in the key hole.

They just happen to be the right shape.

The other way to block Estrogen is by inhibiting the enzyme Aromatase which is responsible for converting Testosterone into Estrogen.

Substances that do this are called Aromatase Inhibitors, or AIs for short.

The most commonly used AIs are

  • Anastrozole (Arimidex)
  • Exemestane (Aromasin)
  • Letrozole (Femara)

As is the case with SERMs, there are other compounds which have demonstrated varying degrees of aromatase inhibition, but drugs such as Arimadex are by far the most powerful AIs there are if the goal is to suppress Estrogen.

So, just to reiterate…

There are two primary ways of blocking Estrogen:

SERMs and AIs.

Both are effective at reducing overall Estrogenic activity, even though they work differently.

Given that SERMs and AIs both potently block Estrogen, whether you need both really depends on the situation.

It’s unlikely that a cancer patient would need to take a SERM and an AI simultaneously, but many bodybuilders don’t consider their PCT complete without a SERM and an AI.

And that brings us to why people use Estrogen blockers in the first place…

Why Do People Use Estrogen Blockers?

Why do people use estrogen blockers?

Every Estrogen blocker mentioned above was originally developed to treat cancer, namely breast cancer.

You see, Estrogen receptors are particularly dense in breast tissue, so limiting Estrogen becomes imperative in the fight against the spread of cancer.

This is why Estrogen blocking drugs are a first-line treatment for breast cancer.

However, like most drugs, Estrogen blockers are used by people for off-label purposes.

You may know someone at your local gym who uses Estrogen blockers because they think it helps them get a better physique, but research begs to differ.

While there isn’t really any evidence that any Estrogen blocker can actually help you build muscle and perform better in the gym, there is one good reason to use them…

If you’re on steroids!

You see, any steroid that increases your body’s Testosterone levels far beyond the normal range will cause your body to compensate by producing more Estrogen.

So, when you stop taking the steroids, your Testosterone levels decline and your Estrogen levels remain sky-high.

This poses all sorts of risks, including:

  • Gynecomastia
  • Mood Swings
  • Bloating (Water Weight)

So, if you’re taking steroids, it makes perfect sense to use an Estrogen blocker as part of your Post Cycle Therapy protocol.  In fact, in most situations, it would be dangerous not to take some kind of Estrogen blocker.

If you’re not using steroids though–meaning the balance of Testosterone and Estrogen is within the normal range–taking an Estrogen blocker isn’t going to do a whole lot for your physique.

Estrogen Blockers For Building Muscle

Perhaps the most common reason people use Estrogen blockers is because they’re under the impression that they’ll help build muscle.

Everyone knows Testosterone is the real muscle-building hormone.  That’s why steroids are a thing and why millions upon millions are wasted every year on herbal Testosterone boosting supplements in the hopes that they’ll help pack on lean muscle.

While it is true that increasing Testosterone can dramatically increase the amount of muscle you can pack on, Estrogen actually plays an important role in building muscle as well.

Suppressing Estrogen only marginally increases Testosterone levels. Certainly nowhere near the point where muscle growth is accelerated.

Simply reducing your Estrogen levels while maintaining the same level of Testosterone won’t help you build muscle.

In fact, because Estrogen plays such an important role in bone health, it stands to reason that lowering Estrogen levels for too long could potentially have a negative impact on skeletal muscle.

The truth is, you need both sex hormones (Estrogen and Testosterone) to maximize muscle building, Testosterone just gets all the glory.

Estrogen Blockers For Fat-Loss

A common misconception is that Estrogen blockers help cut fat.

While it is true that high Estrogen levels can result in water retention (bloating) and weight gain, there’s no evidence that suppressing Estrogen levels can facilitate fat loss.

In fact, there’s only evidence to the contrary.

You may lose some water weight while taking an Estrogen blocker, but you’re unlikely to lose a noticeable amount of fat.

Testosterone, on the other hand, has inherent fat-burning properties.

That’s why people on steroids (the boost Testosterone) are able to get much leaner than those who remain all natural.

Someone like that might use an Estrogen blocker or two as his/her PCT, but an Estrogen blocker alone won’t make you super lean.

What About Supplements That Claim To Block Estrogen?

Estrogen Blocker Supplements

If you stumbled across this post, it’s probably because you’re considering a supplement that claims to be an Estrogen blocker.

Well, sorry to be the barer of bad news, but most Estrogen blocking supplements don’t actually work…like, at all.

We’ll just discuss a few of the most common “all natural” Estrogen blockers, but make no mistake, they have no practical use in situations where suppressing Estrogen is actually important.

Grapeseed Extract

In vitro (not in humans), Grapeseed Extract has shown some anti-aromatase activity.  However, it has failed to block Estrogen in when studied in actually human subjects.

A 2016 study published in The Journal Of Dietary Supplements pretty much put the nail in the coffin for Grapeseed Estract as an Estrogen blocker.

It failed to have any kind of meaningful impact on Estrogen levels, even at higher doses.

Grapeseed Extract may have other benefits, but as an AI, it falls short…

Tongkat Ali (Eurycoma Longifolia)

Eurycoma Longifolia, also known as Tongkat Ali or Longjack, is one of the most commonly included ingredients in supplements designed to block estrogen and/or boost Testosterone.

It’s been shown to reverse estrogenic effects in mice treated with Estrogen.

Similar anti-estrogen effects were noted in another rodent study as well, but so far no human studies have confirmed these findings.

Tongkat Ali may block Estrogen a little bit in mice, but we can’t conclude with any certainty that it does anything remotely meaningful in humans.


Resveratrol is yet another naturally occurring compound which has demonstrated some anti-estrogen effects in vitro and in animals.

Human studies are non-existent though.

Even if it does have some small effect on Estrogen, the impact isn’t likely to be particularly meaningful, rendering Resveratrol an impractical solution for blocking estrogen when it really counts.

You should definitely not be relying on something like Resveratrol for your PCT supplement.

Estrogen Blocking Supplements That May Actually Work

While the vast majority of so-called Estrogen blockers are complete nonsense, there are actually some compounds which appear quite promising…

They’re still in the early stages of research (no human studies), but so far these compounds appear much more powerful at suppressing Estrogen than any of the previously mentioned supplements.


Androsta-3,5-diene-7,17-dione is a metabolite of DHEA which has shown to inhibit aromatase with a degree of potency that is unmatched by any other supplement promoted as an Estrogen blocker.

In fact, research suggests that it’s just as potent as some prescription AIs.

Because it’s a metabolite of DHEA, Androsta-3,5-diene-7,17-dione is perfectly legal to buy and sell as a dietary supplement.

This makes it possibly the only supplement that’s actually an effective AI.

Hopefully future studies give us some more concrete answers, but so far so good.


3′-isoprenylgenistein is one of the few naturally occurring molecules found in plants which has been shown to function as a SERM fairly powerful SERM.

Such molecules are referred to as Phyto-SERMs

And 3′-isoprenylgenistein appears to be one of the most powerful Phyto-SERMs we’ve seen so far.

In fact, like Androsta-3,5-diene-7,17-dione, it’s potency appears to rival that of some prescription SERMs, in terms of how anti-estrogenic it is.

Unfortunately, we don’t have any human studies.  Just a bunch of people who swear by it as their PCT.  It may very well be effective, but only studies can tell us for sure.

Estrogen Blocker Side Effects?

Estrogen Blocker Side Effects

Any drug or substance that actually blocks estrogen can potentially have some negative consequences.

  • Mood Swings
  • Sexual Dysfunction
  • Deteriorating Bone Health

…Just to name a few.

The reality is, you need Estrogen.  You just don’t need THAT MUCH of it if you’re a guy.

So, if you’re on steroids and your Estrogen levels are sky high, it’s a good idea to take an Estrogen blocker that actually works.

If you’re just an athlete or fitness enthusiast looking for an edge, estrogen blockers aren’t worth the trouble.

Estrogen Blocker Legality (It’s Complicated)

Estrogen Blocker Legality

Estrogen blocking supplements (which mostly don’t work) are perfectly legal.  You’ll find Androsta-3,5-diene-7,17-dione in a ton of different supplements these days, mostly geared toward Post Cycle Therapy.

As for drugs like Nolvadex and Clomid, you’re supposed to get a prescription.

However, since these drugs have little-t0-no abuse potential, they are not scheduled in the US.  This means they can be legally obtained for ‘research purposes’.

There are a ton of research chemical websites that sell drugs like Tamoxifen (Nolvadex) claiming they’re “not or human consumption”.

Of course, we all know about 99.99% of the people who buy these drugs aren’t administering them to rats and studying their effects.  They’re using them to come off steroids in order to avoid the negative impact of high Estrogen levels.

So the issue isn’t so much a matter of legality as it is trust.  With all these vendors claiming they have pure SERMs and AIs that will actually block estrogen, how do you know which ones to trust?

Well, that’s why you need to do your research.

Google around.  Read reviews.  Keep in mind that if the price is too good to be true, it probably is.

Plenty of these guys dilute their products because they know most people will never know the difference.  Luckily, there are a few online stores you can trust for your estrogen blocker needs…

These guys all have spectacular reputations for providing what they claim.

The Bottom Line On Estrogen Blockers

The Bottom Line On Estrogen Blockers

Taking an Estrogen blocker won’t do much in the way of increasing lean mass or reducing fat mass.

It’s Testosterone that builds muscle and burns fat, and reducing Estrogen doesn’t mean you’ll produce enough extra Testosterone to gain muscle faster or more efficiently.

This explains why low Estrogen levels can eventually lead to problems with steroid (Luteinizing Hormone, Testosterone, Growth Hormone) synthesis, not to mention the side effects we already discussed.

The only legitimate reason to take an Estrogen blocker is if you’re on steroids or pro-hormones.  If you’re running a lighter compound (Anavar, Epistane, Halodrol, etc.), then you could probably get away with a solid PCT supplement.

If you’re running harsher compounds for long periods of time, you’ll need a more powerful Estrogen blocker, so you should probably get your hands on some Nolvadex.

I’m Matt Theis, founder of SuppWithThat, Momentum Nutrition, and Singular Sport. I created SWT to separate the science from the hype and publish accurate, research-based information on supplements. If you like what I have to say here, feel free to check out my supplements at and

Click to comment
To Top