With some medical conditions Viagra can be ineffective or even dangerous to take. So be sure to consult with your person medical advisor about using Viagra if you have the following conditions:

- consumption of any prescription or nonprescription medicine, herbal preparation, or dietary supplement
- allergy to medicines, foods, or any other substances
- deformed penis (Peyronie disease, cavernosal fibrosis), blood diseases (sickle cell anemia, leukemia, multiple myeloma), or other conditions that may lead to priapism (prolonged erection after ejaculation)
- eye problems (retinitis pigmentosa, sudden vision loss, optic neuropathy, macular degeneration)
- liver or kidney diseases, blood pressure problems, ulcers, bleeding problems, heart problems (heart failure, irregular heartbeat, aortic stenosis, angina), or blood vessel issues
- recent heart attack, stroke, or life-threatening irregular heartbeat

Some drugs can interact with Viagra and cause negative side-effects or even damage your health. So make sure you have consulted with your doctor about taking Viagra if you are taking the following medications:

- Alpha-blockers , amlodipine, high blood pressure medicines, nitrates, or nitroprusside that may cause severe low blood pressure with dizziness, lightheadedness, and fainting
- Azole antifungals, cimetidine, H2 agonists, HIV protease inhibitors, macrolide antibiotics, or telithromycin that may increase the intensity of Viagra ’s possible side effects
- Bosentan or rifampin that may decrease the overall effectiveness of Viagra