Top OTC Anti-Estrogens for Post Cycle Therapy

Anti-estrogens have many purposes for the chemically enhanced athlete. Many of the drier contest prep androgens that bodybuilders use gain much of their affect due to antagonizing estrogen at both the receptor site and inhibiting its creation all together. For those that wish to not use anabolics then anti-estrogens are much desired because they can help you achieve a better hormonal alignment without actually having to ingest hormones.

Benefits of anti-estrogens

  • Prevent (or reverse) gyno
  • Reduce estrogen related bloat
  • Ensure a cycle with aromatizing androgens is drier/leanerIncrease testosterone levels – very beneficial during PCT (post cycle therapy)
  • Aid in fat loss (estrogen is a lipogenic hormone)

Aromatase is the enzyme that converts male hormones to female estrogens. It is the primary way men create estrogen and failure to control this on cycles of aromatizing androgens like M14AD may produce very unsightly side effects. The most commonly used OTC anti-estrogens work through inhibiting this enzyme, and they will be covered below.


ATD ( 1-4-6 androstatriene-3-17-dione) is a supplement that gained huge exposure in numerous OTC PCT (over the counter post cycle therapy) products over the past several years. It is a suicidal inhibitor of the aromatase enzyme, meaning that once the drug has been discontinued enzyme levels slowly return to baseline. Suicidal inhibitors are often preferred because there is no “rebound” in estrogens after coming off.

Scientific data on ATD shows it to be an effective anti estrogen and also would lead you to believe it produces immense increases in testosterone, however other data shows it produces a steroidal metabolite known as 1,4,6 Testosterone. The production of this weak androgen (about ⅓ the potency of testosterone) causes false readings on testosterone serum tests.ATD has huge amounts of anecdotal feedback claiming it markedly reduces sex drive, but it was largely speculated that this was due to a substantial decrease in estrogen (low or high estrogen in males will reduce libido). Scientific literature has pointed us in another direction and shown that ATD is actually anti-androgenic (the complete opposite of what we would want).

The claims that this is great in PCT (post cycle therapy) are nil when the data has been observed. It will reduce estrogen, but also occupy the androgen receptor and not allow testosterone to bind. The 1,4,6 testosterone metabolite would also theoretically produce HPTA suppression if the dose is significant.

Formestane, Lentaron

Formestane (4-Hydroxyandrost-4-ene-3,17-dione) is another suicidal inhibitor of the aromatase enzyme. It was originally studied as a pharmaceutical injection treatment for breast cancer but was pulled off the market in favor of other anti-estrogenic drugs. Formestane has been shown to reduce estrogen content within the body by 50%, so while not being as potent as some pharmaceuticals it does provide a nice reduction in levels.

Formestane will convert to the substance 4-hydroxytestosterone within the body, and this may make it hinder recovery if used during PCT (post cycle therapy). Formestane and 4-hydroxytestosterone can inhibit the enzyme 5-alpha reductase, which is responsible for creating DHT. This also makes formestane a less desired approach to combat gyno because DHT is our bodies natural defense against estrogen. Studies even show that DHT therapy alone can reverse gyno in men, so it isnt exactly something suitable if reducing it might cost you a pair of moobs. Reduction of 5-alpha reductase is favorable for those prone to male pattern baldness, so those ingesting aromatizing androgens may have a safer bet using formestane to mildly reduce androgenic hormones and also estrogen if hair loss, but not gyno, is a concern. Formestane has very poor oral bioavailability so a transdermal preparation is often the preferred mode for ingesting this substance. If oral products are to be used doses should be 150+mg per day.

Arimistane, Erase

Arimistane (Androsta-3,5-diene-7,17-dione) is the newest anti-estrogenic compound on the market. It is a suicidal inhibitor like the others above but has a few distinct alterations. First, this compound is unable to convert to a steroidal metabolite. This means that it is very favorable during PCT (post cycle therapy) because HPTA suppression is impossible. The 7-oxo that this compound has also makes it good at reducing the catabolic hormone cortisol, which spikes after coming off your cycle.

Studies on the affinity for the aromatase enzyme show that this compound is actually more potent than the pharmaceutical compound Aromasin. The difference in bioavailability between the two is in favor of Aromasin, so that means that this compound would need to be ingested at slightly greater dosages (50-75mg vs 25mg).

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