Clenbuterol can cause a downregulation in testicular androgen receptors, possibly making steroids less effective (if there is androgen receptor downregulation elsewhere as well, then it´s highly probable) while you are on clen; but definitely making clen less effective as time goes on and you keep taking it. To counteract this, you can take some ketotifen every 3rd or 4th week that you remain on clen. It´s a prescription anti-histimines, so it´ll make you drowsy (take before bedtime). Basically, the way this works is to reduce beta-2 receptor activity, and restore receptor function.