hey, give this a read before you start the clen :
"Clenbuterol should be built up and tapered off gradually with dosage increases and decreases every 3-4 days and doses never exceeding 160 µg per day to be perfectly safe. Its mostly used for periods of 2-3 weeks then discontinued for equal periods of time to disallow the body to adapt to the effects of the drug. For fat-burning goals clenbuterol is often stacked with another fat-burning agent for quick effect, or alternated with another fat-burning agent by people who need to stay lean on a year-round basis. Usually cytomel (T3) is used for such purposes, with alternating cycles of 3 weeks each. If used together, cycles will not completely overlap, but differ slightly so as not to match the low doses with the low and the high doses with the high. A typical cycle for clenbuterol might be 3 weeks, with the daily amounts being 40/40/40/60/60/60/80/80/80/100/100/100/80/80/80/60/60/60/40/40/40 µg/day. Then stopping for three weeks and recommencing.
It's also commonly stacked with anabolic steroids. Usually non-aromatizing steroids that give the user a leaner and harder look, and allow for less water retention. They serve a main purpose of allowing the user to keep as much of his hard-earned muscle mass as he tries to shed the fat he has stocked up in the off-season with catabolic precursors such as clenbuterol. Clenbuterol is generally regarded as fairly safe6, hence its wide-spread use. It should be disadvised for all with blood pressure and/or previously diagnosed cardio-vascular problems. But most tolerate it quite well. By building up the dose over time they usually see when they've reached a dose that becomes too harsh. The use of clenbuterol will elicit higher body temperature, higher blood pressure and in some, especially at high doses, insomnia and jitters. Though these should not be nearly as pronounced with clenbuterol as they are with ephedrine and its legal counterpart ma huang. They are also easily remedied by shifting doses around so you don't take clenbuterol in the hours leading up to bedtime and most of it in pre-training phases when the drug can enhance your training vigor.
Another good match for clenbuterol in a stack is the plant derivative yohimbine Hcl. It does concern the standardized product yohimbine here and not the raw material yohimbe, which is useless. In small doses of 20-30 mg per day, it can stop the down-regulation of the noradrenaline feedback mechanisms, that usually inhibit the actions of noradrenaline by reducing receptor affinity. This has two important uses. The first is that the length of action of clenbuterol can be enhanced by a few hours when using it together with yohimbine Hcl (although it already has a considerable half-life time7 of 36 hours and one daily dose should suffice) , and the second is that concomitant use of yohimbine Hcl may allow clenbuterol to induce its fatburning aspects on a longer term than the normal 2-3 weeks, so it can be used for 5-6 weeks instead. Yohimbine Hcl is, at least for now still, a legal supplement that can be acquired for very little money from legal sources and supplement companies. "
source
http://www.bodybuilding.com/fun/catclen.htm