Zyrtec accumulated two months before first O, that's when I found out it worked. But, I had already been seeking and getting relief from Claritin and the two Benadryl combo for over three years at that point. That's when I went to the urologist (after the 3 years on Claritin) and he then told me to get on Zyrtec, since it was more powerful of an anti-histamine than Claritin. I took for two months, then had first O being on the Zyrtec, and that's when it cleared up my symptoms 100%. Two years later, now, and for the previous 4 weeks I've been able to stop the Benadryl for the first time in 5 1/2 years. I only take Zyrtec now. I don't give medical advice, that's what doctors do. But, because of my previous experience and lack of a total cure being found yet for the treatment of everyone, I would say, take Zyrtec for at least two months, and I repeat do it for the full two months, and then try the two Benadryl immediately following your O. Take it within 20-30 seconds following O for it to work completely. The Claritin the first time (5 1/2 years ago) worked wonders after only a 30-day trial combination with the 2 Benadryl following O. Maybe take the Zyrtec for 1 month, stick it out, then O and try the Benadryl. Good Luck!