Clenbuterol can also cause a downregulation in testicular androgen receptors and in pulmonary, cardiac and central nervous system beta-adrenergic receptors(6.) 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 (15).
Another option, if you are worried about receptor downgrade, is taking Benadryl, at around 50-100mgs/night before bed (every 3rd week or so, for that week). Benadryl is sold as an anti-histamine in the United States, and/or a sleep aid elsewhere in the world. However, Beta receptors are embedded in the cell´s outer phospholipid membrane. The stability of the membrane has a lot to do with the proper function of the receptors. Methylation of the phospholipids is stimulated by the binding of beta agonists to their receptors. Methylated phospholipids are foreign to the body, and when the body recognizes them as foreign, it breaks them down with phospholipase A2. This changes the structure of the outer membrane which results in desensitization of the beta receptors. On the other hand, agents that inhibit phospholipase A2 slow desensitization.
(15)Z Erkr Atmungsorgane. 1990;175(3):141-6