If you used HCG for a long period of time then yes just like anything I sure you may have problems. The duration of the use in this post cycle therapy will be virtually harmless and because it is water based it will be out of your system in as little as 24 hours. If you are concerned about estrogen use nolvadex to block it. I think you should do some research on what ever you decide to take, cause most of you AS will convert to estrogen and if your predisposed to them side affects even a small dosage could affect you.