Before taking Viagra, tell your doctor if you have: sickle cell anemia (an abnormality of red blood cells), leukemia (blood cancer), multiple myeloma (cancer of the bone marrow), heart disease, liver disease or illness / deformity of the penis, what that it is. In these cases, it may be necessary to take special precautions when taking medications for the treatment of erectile dysfunction; recently been the victim of an attack or myocardial infarction, or if your blood pressure is low; rare eye disease (such as retinitis pigmentosa), gastric ulcer or disorder of blood clotting (eg, hemophilia). Viagra may have adverse effects on these diseases. Do not use Viagra at the same time as another treatment for erectile dysfunction. Inform your doctor about all medications you are taking. Viagra tablets filmed can interfere with other medications, especially those used to treat chest pain. Do not take Viagra with other medicines if your doctor told you that you can. Viagra can seriously enhance the effects of drugs that contain nitrates, or substances which release nitric oxide (eg molsidomine, the nytroglycerine or similar substances). These are drugs often used to alleviate problems caused by angina pectoris (or "heart pain"). You should not take Viagra if you are using these drugs. Similarly, you should not use amyl nitrite, a substance sold illegally contained in so-called "poppers". There are a number of drugs that slow or prevent the degradation of the active ingredient of Viagra in the liver. The effect of Viagra is strengthened but its adverse effects, including the frequency and severity may increase. Among these drugs are among some other antibiotics ("macrolides" such as erythromycin), medicines against fungal infections (eg ketoconazole), certain drugs used in AIDS (protease inhibitors) or drugs against excessive gastric acid secretion or gastric ulcers, which is the active ingredient cimetidine. If you are taking protease inhibitors for the treatment of HIV, your doctor may prescribe Viagra starting with the lowest dose (25 mg). Please tell your doctor if you are taking anticoagulants (medicines to "dilute" the blood) or drugs to lower voltage is too high. If you suffer from any disease, if you have any allergies or if you are taking other medicines (even self-medication), notify your doctor. Taking Viagra may occasionally cause dizziness and blurred vision (lasting several hours), such as blurred vision or abnormal color perception. It is therefore necessary that you know how you react to Viagra before driving or you use a machine. It must also be taken into account for activities where a clear distinction of color is essential.