What is aromatization?

It’s a natural process that happens all the time in your body, when your aromatase enzymes convert testosterone into estrogen. 

It’s important to understand that aromatization is NOT your enemy. It’s crucial to maintain a healthy estrogen level in the body. Yes, even though you are male, some female sex hormones, in minuscule amounts, are still necessary.

What are aromatase enzymes?

Aromatase enzymes are just proteins in your body that are built to perform this conversion. These enzymes are found in many tissues, including (and mostly in)  fat cells, skin, liver, and brain.

Just in case you were curious, aromatization and aromatase are called this way because of the aromatic ring in their structure (a ring-shaped molecule with alternating double-bond atoms).

Which steroids do aromatize? The full list

In short, anything that is Testosterone or Testosterone-like can be turned into estrogen. 

Here’s the list of the most popular aromatizing steroids that aromatize: 


Test obviously aromatizes, in all its forms, including esters, like Enanthate, Cypionate, Propionate, Decanoate and non-esterified versions (Testosterone Suspension, Testobase). 


Dbol DOES aromatize, because methandrostenolone is basically a modified testosterone molecule.

Deca Durabolin and NPP

Both Deca and NPP are Nandrolone-based, and both ARE aromatizing. You need to note that nandrolone aromatizes 5 times less effectively and twice as slow as Testosterone does, so we can say that Deca is MILDLY aromatizing.


Equipoise, aka Boldenone, is another example of a compound that can be a substrate for aromatase enzymes, though not really an effective one. It’s also mildly aromatizing, if aromatizing at all (depends on your individual response). 

Which steroids do NOT aromatize? The full list

Some compounds are either not built for aromatization from the start or were modified to avoid it. 

Here’s a list of compounds that do NOT require aromatase inhibitors on cycle:


It’s not just safe in terms of aromatization, it’s also a weak anti-estrogen itself. Masteron, however, still requires caution with dosing, it’s still not the safest compound available.


Oxandrolone, aka Anavar, is a mild strength booster that’s based on DHT (aka dihydrotestosterone), not on Testosterone itself, so it can’t aromatize.


Anadrol is also DHT-based, so you don’t really need an AI with it. It’s still heavily estrogenic, though, so you have to be careful.


Stanozolol (on the market as Winstrol) is made using a DHT molecule as a basis, so it’s also safe in terms of aromatization. It’s true for both oral and injectable Winstrol options.


Primo is the final DHT-based substance that can’t structurally be aromatized. 


Even though Tren is made with Nandrolone as a basis, it does not aromatize at any significant rate because of the modified structure. 

Specifically, it has a double bond at the 9th and 10th carbon atoms (in simple terms, the «binding» site for aromatase is removed, so it can’t even connect to the molecule, let alone convert it). 


Even though it’s derived from Testosterone, Turinabol is structurally modified with a so-called chloro group that resists the aromatization. 

What is considered a normal aromatization?

Just as we said earlier, aromatization itself is not a bad thing. It’s vital to keep your body healthy and functional.

Unfortunately, it’s a strictly individual process, with some men being heavy aromatizers (aka they have a lot of aromatase enzymes and those are exceptionally active), and some being the opposite. 

We can’t really measure aromatization rates once and for all. We CAN, however, measure the result of aromatization: estrogen. 

Healthy estrogen level for men

The only way to check it is by doing bloodworks. When you get your result, the estrogen will, most likely, be measured in picograms per milliliter (pg/mL). 

Most likely, you won’t get an “Estrogen” graph in the results, since “Estrogen” is just a term used to describe a whole group of similar hormones: estradiol, estrone and estriol. 

Estradiol, aka E2, is the one that you should be looking at: 

Anything between 10 and 40 pg/mL is considered a normal level of E2 for a healthy male.

Note that those figures are individual. Maybe your minimal comfortable level is at about 12.5 pg/mL, maybe you’ll feel OK with your E2 at 45 pg/mL.

The best thing you can do here is just using the figures as a reference point and a signal to watch out for red flags — high and low estrogen side effects. SOme of them are really hard to miss.

Low estrogen side effects:

  • Fatigue and lethargy;
  • Dry and less sensitive skin;
  • Low libido and inability to get an erection;
  • Depression, anxiety;
  • Nervousness, aggression, irritability.

High estrogen side effects:

  • Inability to get an erection, low libido;
  • Faster fat gains, water retention;
  • Oily skin, acne, increased sweating;
  • Disrupted sleep patterns, sleepiness or inability to fall asleep;
  • Aggression, irritability, nervousness;
  • Blood pressure issues, higher risk of heart disease;
  • And finally, gynecomastia, aka male boobs.

As you can see, both high and low Estrogen is bad. You need to keep it under full control, within the normal range. 

Since aromatizing anabolic steroids are more likely to push you above the healthy limit, to keep E2 in the healthy frames, you need to lower it and decrease your aromatization rate. 

And this is exactly what aromatase inhibitors do.

What are aromatase inhibitors and when you need them? 

You need AIs on cycle, alongside all the gear that you run, to keep E2 levels in check.

Aromatase inhibitors are made to inhibit (deactivate) aromatase enzymes. Arimidex, Aromasin and Femara do it in 3 different ways with the same result — lower estrogen. 

Note that you should be careful with ALL aromatase inhibitors, regardless of their mechanism of action, since all three are capable of completely destroying your E2 and practically replacing high estrogen side effects with low estrogen side effects. 

Which AI to choose?

In an extremely short and oversimplified description, you need:

  • Arimidex — when your E2 is extremely high;
  • Aromasin — for proactive on-cycle support and if your E2 is higher than normal, but not THAT high;
  • Femara — only when you already have gynecomastia and other high estrogen side effects, since it’s the newest and the most powerful AI option.

Each aromatase inhibitor requires individual approach and further research, if you want to take it safe. Here are the basic guidelines, so you can take each of them with actual beneficial results, not extra problems.

Arimidex aka Anastrozole

  • Effectiveness: lowers E2 by about 50%
  • Level of caution when using it: moderately high
  • Half-life: 48 hours
  • Dosage: 0.5mg E3D

Arimidex, or just Adex, is considered to be a basic aromatase inhibitor. It’s not that bad in terms of side effects (it still surely will mess with your cholesterol), it’s not powerful enough to be unforgiving (just take moderate doses), and it’s effective enough to lower your E2 in a matter of 1-2 weeks, even if E2 is significantly higher than it should be. 

We say that you should be cautious when using it because Arimidex is one powerful compound, but it’s actually quite safe in terms of long-lasting side effects: even if you make a mistake with dosing and accidentally push your E2 below the healthy limit, it will get back quickly, when you return to a normal dose.

Aromasin aka Exemestane

  • Effectiveness:  lowers E2 by about 30-60%
  • Level of caution when using it: moderately high
  • Half-life: 30 hours
  • Dosage: 12.5-25 mg ED

Aromasin is a milder, more flexible option, perfect for on-cycle support because of all the extra benefits it brings. In addition to effectively lowering your estrogen, Aromasin can lower SHBG (sex hormone binding globulin) and give you more free testosterone, meaning that you get more muscles.

It’s also less toxic than other AI options for your liver. However, we still say that you should be cautious, because it’s not as forgiving as Arimidex. 

If you take too much Aromasin, your aromatization will need a lot of time to get back to normal. All that time (hard to predict how long exactly, strictly individual) you’ll have to “enjoy” the low-E side effects. Sadly, as a counter-balance for all the extra positive effects, Aromasin is notoriously effective at boosting hair loss.

Femara aka Letrozole

  • Effectiveness: lowers E2 by 75 to 95%
  • Level of caution when using it: extremely high
  • Half-life: 48 hours
  • Dosage: 1.25mg ED

Letrozole (Femara) is the new generation of aromatase inhibitors, essentially a modified and improved Arimidex. However, Femara should be your last resort when it comes to E2 lowering. It's just too powerful and too harsh in terms of side effects. You can expect a crashed lipid profile, insomnia, higher blood pressure, zero sex drive and joint pain. 

Femara should be used exclusively when it’s the lesser of two evils: 

  1. If your E2 is through the roof and you experience a whole spectrum of estrogenic side effects;
  2. Or if you already have notable gynecomastia (not just increased nipples sensitivity). 

As a last resort measure, Femara is probably the best AI you can get. It might be a good proactive measure if you tolerate it well, but most athletes prefer Aromasin or Arimidex for basic on-cycle support.

The Wrap up

Aromatization is your body’s way of keeping things balanced in your hormonal profile. As pretty much everything in your body, it’s complex, defined by a whole ton of aspects, and fragile. When you intervene in this process with anabolic steroids, you should make up for it: do the opposite of what you’ve done already.

Unfortunately, the role of E2 in male body is often overlooked. Novice athletes just label it as an enemy and don’t bother with trying to keep it balanced.

You can be smarter than that. Hopefully, with this guide, you won’t just try to “kill female hormones” in your body, but will use all the precise tools you have — AIs — wisely, to maintain balance in your hormones.

As the heading goes, the only way to win your fight with aromatase enzymes is by keeping them balanced, controlling them, not fighting with something that your body relies on naturally.