I'm not a doctor and I don't play one on tv, however I can google...
Here are a couple relevant details for ya:
- clenbuterol is a bronchodilator -- relaxes the bronchial tubes. Also apparently used to relax the uterus. (Interesting, I didn't know that...) It mentions don't use it in the first trimester of pregnancy. http://www.inchem.org/documents/jecfa/jecmono/v38je02.htm
Its a pretty short time actually. Just like when we talk about clen cycles of 2 weeks on / 2 weeks off, after 2 weeks off, the affected receptors have been cleared.