My rats are currently on a TRT replacement program that includes 200 mg T with 600 units of hcg twice weekly injected, and 0.25 mg of Anastrozole daily. Since trying the rat tested formula of A., and noticing the exact same side effect of the compounded and very expensive human tested material, I've opted for the cheaper rat tested variety, without hesitation. Using the easier to measure rat tested formula, I've noticed the rat's sex drive dramatically increases if the dose is raised and the reverse when lowered, on a week over week basis, from as high as 1 mg per day to as low as 0.1 mg per day. What's interesting, and unexpected in my results, is that the change in libido occurs when the A. dosage level is increased, and usually within a day. The usual increase or decrease on a week over week basis is approximately 0.1 - 0.2 mg. Why on the upswing, if as I've read here, the higher estrogen levels actually increase libido, and if you dampen it too much, you lose libido? Given the importance of some estrogen to libido, I would have expected an increase in libido, at least when dropping from 1 mg per day, to say .... 0.5 mg, as opposed to the reverse. My gut feeling is that the increase in libido is resulting from the additional testosterone conversion. The rat is fit, but overweight ... however not obese. I would say moderate belly fat. So this may have some influence on these unexpected results. So is the added T. conversion likely the cause of the increase in libido, and the estrogen just a null factor due to the excess weight and body fat? Does anyone have a technical opinion of this. The results are so consistent, that I'm sure of what I'm seeing. There's been no real reason to go outside of the normal blood work routine, which is about every six months or as needed. The numbers stay about the same, and this includes the lower levels recorded during TRT vacations. It's obviously not something I would recommend to anyone else, but anyone who has watched the movie Young Frankenstein knows these things are sometimes unavoidable, within reasonably safe parameters. The rats enjoy their moments of exceptional glory.