Key Takeaways

• Both SERMs and AIs can decrease Estrogen 
• SERMs only decrease Estrogen at the breast tissue, AIs reduce Estrogen everywhere 
• SERMs are more often used in the PCT to increase Testosterone production 
• You can use both together, but there is barely ever a need for it 

Before we get started, we first need to understand the nomenclature difference between these two: 

• SERMs or Selective Estrogen Receptor Modulators are something that will mostly act upon blocking estrogen in the breast tissue. They will not make you drier or help you lose water weight, they solve one problem and one problem only – Gyno. They can, however, be used to increase LH and FSH levels as well. Another positive feature these have is that they seem to promote estrogen in other parts of the body (which is very healthy) 
• AIs or Aromatase Inhibitors are the big boys. Imagine bringing a Nuclear Bomb to a pot roast. AIs are going to be used to stop gyno, remove any (and sometimes all) estrogen from the body, and make you as dry as you can possibly be. These are also used to control estrogen while running a cycle that is high in aromatizing compounds 

Those are the main differences between the two. So, when would you use one or the other? 

We know that using certain Steroids can cause a reaction in the body of increasing estrogen. Contrary to what you might have heard, this is actually perfectly healthy! In fact, higher estrogen could help you build more muscle. That said, it can also lead to fat gain. To gyno. To emotional instability. 

So, controlling it would be best. 

This is where you have various options at your disposal, each one better than the one before: 

• Using a DHT-Based Steroid as an AI: You might be surprised to learn that products such as Masteron (DROSTANOGEN (Masteron Enanthate)) and some other DHTs can actually act like lower-tier AIs. They certainly won’t be as good as the other compounds on this list, but it isn’t uncommon to add some to your TRT (thus making it HRT) to control Estrogen 

• The way to control or save Gyno is with a SERM: Many of you already know that having elevated estrogen can lead to the development of breast tissue, and inflated prolactin can cause lactation as well. While Prolactin can only be controlled with Cabergoline of Vitamin B6, Gyno can easily be controlled with a SERM. Why a SERM and not an AI? Well, technically, AIs are not going to be tissue-selective. They drop estrogen in the entire body, which is not a good thing. Estrogen is vital for health, and destroying all the estrogen in the body will lead to some serious side effects. SERMs are tissue-selective to the breast, meaning you will only be blocking estrogen there. You will be increasing estrogen everywhere else! 
• AIs are best kept for bodybuilders or those who use a ton of AAS: It will come as no surprise that bodybuilders use a lot of steroids, some even north of 3000mg per week. This means a large portion of those compounds will convert into estrogen via the aromatase enzyme. Again, not something to be too worried about, but there can be too much of a good thing. When you start running into issues of fat gain, water retention, emotional instability, and gyno, it is time to use an AI. 

So are those the only times you would ever need to use one of these products? No, there is one more scenario where you would use these – to increase Testosterone production. 

Because SERMs bind to the Estrogen receptors in the body but do not act like estrogen itself, the body will sense “low estrogen”. Where does the male body get estrogen? From converting testosterone into estrogen! Thus, by taking a SERM you can trick the body into increasing LH and FSH levels, causing an increase in basal Testosterone production (note that both SERMs and an AI would theoretically increase Testosterone production. SERMs are just better at it.)

LH or Luteinizing Hormone will cause the release of Testosterone in men, especially those that have been shut down due to steroid use (Human chorionic gonadotropin (hCG)) is an analogue of LH. 

FSH or Follicle-Stimulating Hormone is a hormone that helps with the production of Sperm in men. It also aids in Testicular growth.