The use of Clenbuterol results in down regulation of beta receptors, and therefore, it is should be used for only short periods of time. A clen cycle generally lasts 2 to 3 weeks with a break in between cycles lasting equal to or longer than the cycle itself. The cycle should start gradually, slowly increasing the Clenbuterol dosage and then tapering off gradually. The average dose of clenbuterol is 60 to 120 mcg/day. Your best course of action is to start slow with a low dose, gauge the effects it has on your body, see how well your body handles it, and then slowly increase the dosage accordingly.