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Aromatase Inhibitor (AI) vs. Selective Estrogen Receptor Modulator (SERM)

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  • Aromatase Inhibitor (AI) vs. Selective Estrogen Receptor Modulator (SERM)

    Anyone who wants to use anabolic steroids should take the time to learn about the various products and supplements that will prevent unwanted side effects. Aromatase inhibitors (AIs) and selective estrogen receptor modulators (SERMs) are two very popular – and very important – parts of an anabolic steroid cycle. Understanding the difference between the two is vital to maintaining your health and your physique.

    What Do AIs and SERMs Do in the Body?

    Just as AIs and SERMs are very different, they are also very much the same. Both of these compounds provide ways to control the amount of estrogen in the body, which is vital for preventing some significant side effects.

    Many of the most popular anabolic steroids convert to estrogen, and when too much estrogen is present, you may notice some of the following:

    Decreased libido

    Significant bloating

    Gynecomastia (a condition in which men develop female breast tissue)

    Weight gain



    AIs and SERMs both prevent these side effects, but they do so in very different ways.

    What Is an AI?

    An AI, or aromatase inhibitor, prevents a steroid from converting to estrogen. Androgen is common in anabolic steroids, and some are more androgenic than others are. Once these androgens are in the body, they turn into estrogen over time with the help of an enzyme known as aromatase. An aromatase inhibitor binds to the aromatase enzyme, thereby making it ineffective at converting androgens into estrogen. However, it takes time for AIs to build up in the bloodstream. Arimidex is the most popular aromatase inhibitor among steroid users, but Letrozole is another option for men who are particularly sensitive to the effects of estrogen or who want to reverse existing gynecomastia.

    What Is a SERM?

    On the other hand, a SERM, or a selective estrogen receptor modulator, binds to the estrogen receptor itself rather than the aromatase. While a SERM blocks some of the actions of estrogen, it allows others. Even in the male body, some estrogen is important. While an AI inhibits all estrogen, a SERM just prevents its negative effects by blocking estrogen’s androgenic properties. Two of the most popular SERMs in terms of performance enhancement are Nolvadex and Clomid.

    Which Is the Best Choice?

    While an AI blocks estrogen production and may ward off side effects, bear in mind that the body continues to send chemical signals that it needs more estrogen. As such, the body continues to produce more estrogen, resulting in an endless cycle and sometimes a “rebound” effect in which estrogen levels suddenly spike after stopping the AI. A SERM only affects the way the body uses estrogen, and as far as the body knows, there is plenty of estrogen to go around. Thus, while an AI can prevent unwanted side effects during anabolic steroid cycles, it is imperative to use a SERM during post-cycle therapy to combat rebounds and bring levels back to normal.

    Both AIs and SERMs play important roles for people who choose to enhance their performance with anabolic steroids. However, knowing which product to use in which situation can make all of the difference when it comes to preventing potentially serious side effects.