never had a loss of libido, but I've never run it without test in my cycl which would counter that!! I'd say a coupel days but don't know for sure... began gyno symptoms runnin .25mg ed and had to bump it .5 ed and cleared right up within a few days but I kicked it up as soon as I began gettin irrtated itchy nips but as I reacll it was gone in just a few days!! so it works relatively quick in my opinion!!