It may be difficult to remain firm despite wanting to have sex. Penis deformation: As with other medications for erectile dysfunction, men with an anatomical deformation of the penis such as angulation, cavernosal fibrosis, or Peyronie’s disease should be closely monitored by their doctors if they take this medication. Psychological factors like stress, depression, or anxiety can also contribute. Always seek the advice of your physician or other qualified health providers with any questions you may have regarding a medical condition. For example, the cancer drug Xalkori is an ALK—short for anaplastic lymphoma kinase—inhibitor, while Zelboraf, used to treat melanoma, is a molecule that inhibits the BRAF gene. Shipping: Discreet, fast shipping is a must.Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash. If you’re willing to take the risk, albeit a small one, you can walk into a pharmacy across the border in Canada armed with a prescription for Viagra (make sure your US doctor . VIAGRA can cause your blood pressure to drop suddenly to an unsafe level if taken with certain other medicines. Do not take VIAGRA if you take any other medicines called “nitrates.” Nitrates are used to treat chest pain (angina). A sudden drop in blood pressure can cause you to feel dizzy, faint, or have a heart attack or stroke.