I cut and pasted this from another board...good info...

Estrogen causes an increase in the amount of TBG(Thyroid Binding Globulin), which decrease the amount of active T3 in the blood. Conversely, androgens will decrease the amount of TBG in the blood, therefore increasing the amount of active T3. Another way that AAS help to burn fat. So for those that think that AAS don't help burn fat, there's the proof that it indeed does have an effect on metabolism. Proper use of thyroid hormones are a key role in BB, Figure, and Fitness competion prep. Everyone knows this, but very few maximize their results with it. This is largely due to a misunderstanding of how they work and the proper dosage/time that they should be used.
The safest way to use it is 2 weeks on/2 off. Starting with 25 mcgs and working up to 75-100 mcgs/day. It's very important to taper up and down such as follows:
For women, some may need to start off at only 12.5 mcgs/day, which equates to half a tab of Cynomel. I'll often have my athletes use it for up to 8 consecutive weeks. They come off with no problems b/c I have them correctly. When you are confused about the taper always remember that the more gradual the taper, the better it is for your body.