Good question. I never really know. I did notice that with increased sex, there appears to be a tolerance. When using it 1 or 2X per week I saw no tolerance. Since on TRT and getting my cialis from overseas pharmacy sex has been every other day pretty much. Still don't know about tolerance though, because my wife likes the occasional day off from it because she believes it intensifies the response. I think she's right. More sex can possibly create an illusion of tolerance. FL is right. Some guys have a hard time getting over the back problems. Try a low dose of 5 or even 2.5 daily to maintain a baseline and add regular dose when sex is planned.