Arimidex seems to have somewhat become the holy grail of anti-estrogens. Due to its limited availability, high price and extreme effectiveness, its become a much desired product on the black market. The compound anastrozole is indeed a revolution in the treatment of breast cancers. It's a new generation of aromatase blocker. Up until recently the main product for this purpose was the androgenic steroid Mesterolone (Proviron). But the problem here was that Proviron was not particularly strong and in the required doses of 50 to 100 mg per day, androgenic side-effects were not uncommon. Proviron is after all a DHT derivative. It could also never be used longer than the cycle lasted, because to some extent (despite readily being deactivated) it was suppressive of natural testosterone production. Anastrozole seems to do the job more efficiently. In clinical trials a single tab daily proved to have a profound effect. In steroid circles, mostly due to the high cost, experimentation with half and quarter tabs proved it to be almost unbelievably strong. So much, that really half a tab per day suffices for most users.
Anastrozole operates by blocking the aromatase enzyme, the primary enzyme for the conversion of testosterone to estrogen. A steroid that is altered by this enzyme is referred to as an aromatizing steroid, and such steroids can cause estrogen build-up. This has several potential side-effects such as water retention, fat gain and lets not forget gynocomastia (the growth of breast tissue in men). To prevent such effects anti-aromatase products can be used. Often times during a cycle most will want to allow for some estrogen, since it heavily promotes strength and gains as well (increases GH, upgrades the androgen receptor, improves glucose utilization). These people will generally opt for an estrogen receptor antagonist such as Nolvadex (tamoxifen) or Clomid (Clomiphene). These products do not stop the formation of estrogen, but stop the estrogen from exerting its effects by competitively taking up the receptors for this hormone. This allows them to stop any problems dead in their tracks, acting very fast, but upon discontinuation allowing for immediate influx of estrogen again as well. This has the benefit that they can be used as soon as problems arise, and discontinued when they subside, thereby only reducing estrogen-mediated gains for the time-span of the occurring problem (mostly gyno). Aromatase blockers like arimidex and proviron on the other hand are more useful for those seeking to eliminate estrogen from a cycle of aromatizable steroids all together. People who are willing to settle for slower gains, in an attempt to stay lean throughout, or for those who are truly sensitive to estrogen and do not want to take the risk of problems occurring. And arimidex is the clear weapon of choice here, at least to those who can afford it.
Things one needs to note while using arimidex is that the benefits of estrogen become non-existent as well. First of all that means gains can be drastically reduced. They will be leaner and more qualitative, but they will nonetheless be seriously reduced. A second problem is that estrogen seems to have a positive effect on cholesterol levels. Since estrogen is reduced, the use of arimidex may have a profound impact on HDL to LDL ratio's in your cholesterol profile. In this aspect the use of Nolvadex is more user-friendly, because despite its anti-estrogenic effects in most tissues, it seems to exert positive estrogenic effects in the liver and promote a better cholesterol profile.
Lastly, the major problem with arimidex is the cost. I've seen people who were willing to fork over 250 dollars for a 28 tablet box of legit arimidex. That's the price of fame. Of course these prices are rididculous, but most people don't really know where to look. I've found the generic anastrozole tabs for as low as 2.2 dollars per tab, which is less than half the average street price. So it all comes down to shopping around a bit. Its not that anastrozole is that expensive to make, just that its patented. Which means that besides legit arimidex, all versions in existence are generics. This also means they could be slightly off on content or impure, if trustworthy at all. So be sure to check this with someone who has tried them or had them tested before buying a generic. The liquidex sells legit for not that much more, Around 3 to 4 bucks per gram and is generally a good buy as well, although content may be off. Since few will be investing in this to mess around with low doses and will generally opt to take 1 mg a day (1/4 cc), this shouldn't be a problem. The anastrozole powder is a real buy at merely 2-3 dollars per mg, but obviously no one will ship that for less than 100 mg orders.
As mentioned, arimidex is an ancillary that is supposed to be stacked with aromatizing steroids in order to stop all formation of estrogen. Its seemingly very potent, so doses of 0.5 to 1 mg are enough. Some claim that 0.25 mg is enough, but for anyone doing any sort of serious cycle, I would not advise less than 0.5. These steroids are, without exception testosterone, nandrolone, norethandrolone, boldenone and methandrostenolone. And all of their derivatives as well. The drug oxymetholone (anadrol) has estrogenic effects as well, but they seem to be the result of oxymetholone's acidic A-ring activating the estrogen receptor by itself, rather than by conversion to estrogen. So Nolvadex would be more advisable in that case. To understand the whole story, I refer you to my profile on Anadrol.
Although it does block gains, aromatase blockers are generally used for the extent or a certain duration on a cycle, whereas receptor antagonists are used mostly to solve problems. Because it takes some time for an aromatase blocker to take effect (even when aromatase is blocked, there is still a level of circulating estrogen) and again some time to bring estrogen back upon discontinuation (new estrogen needs to be made again), acute problems are best solved with Nolvadex or clomid. When an aromatase blocker is used, Arimidex is the best choice by far. Proviron may be more apt when using with testosterone, due to its other characteristics and positive benefits on testosterone, but for all other intents and purpose arimidex should be preferred in these instances.