Although disbelieved and not adhered to by some, the following is scientific fact:

Take your Clen in the morning, to permit enough time for the stimulant property to dissipate preventing insomnia in all but the most sensitive of individuals. Due to their naturally occurring drowsy promoting side effect, first generation antihistamines (such as Benadryl) are the preferred sleep aids while on Central Nervous System (CNS) stimulants. While performing their primary action of cleansing the beta receptors of the allergen histamine, they simultaneously upregulate/cleanse said receptors of residual substances also absorbed at this level, which coincidentally includes CNS stims, i.e., Clenbuterol, Sambuterol, Albuterol, Ephedra/Ephedrine, etc. This antihistamine function also affords the continuous cycle use of such stims for greater accrual effect, i.e. better collective stim results. AR cited this effect in the original S.com Clen profile, and he was correct.