im no expert,but from the resurch i have done peeps take the anti-histamines as a way to clean out the receptors so u can continue running the clen. thay do 2 weeks of clen, then a week of clen+anti-hist,then 2 mor weeks of clen,then clen+anti-hist. for as long as you want to run it. ive read alot of threads on clen cus i am about to do a cycle myself and thats wat i see peeps doing. hope this helps. boyd