Do not take Nizagara, if you are also using a nitrate drug for chest pain or heart problems, including nitroglycerin (Nitrostat, Nitrolingual, Nitro-Dur, Nitro-Bid, Minitran, Deponit, Transderm-Nitro), isosorbide dinitrate (Dilatrate-SR, Isordil, Sorbitrate), and isosorbide mononitrate (Imdur, ISMO, Monoket), or recreational drugs such as amyl nitrate or nitrite ("poppers"). Before taking Nizagara, tell your doctor about all other medications you use for erectile dysfunction, or if you are using any of the following medications: bosentan (Tracleer); a blood thinner such as warfarin (Coumadin); cimetidine (Tagamet, Tagamet HB); an antibiotic such as erythromycin (E-Mycin, Eryc, Ery-Tab) or clarithromycin (Biaxin); doxazosin (Cardura), prazosin (Minipress), Terazosin (Hytrin); HIV medicines such as amprenavir (Agenerase), tipranavir (Aptivus), darunavir (Prezista), efavirenz (Sustiva), nevirapine (Viramune), indinavir (Crixivan), saquinavir (Invirase, Fortovase), lopinavir/ritonavir (Kaletra), fosamprenavir (Lexiva), ritonavir (Norvir), atazanavir (Reyataz), or nelfinavir (Viracept); an antifungal medication such as itraconazole (Sporanox) or ketoconazole (Nizoral); carbamazepine (Tegretol), phenobarbital (Luminal), or phenytoin (Dilantin); or rifampin (Rifadin, Rimactane) or rifabutin (Mycobutin). Tell your doctor about all the prescriptions and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor. If you have heart problems severe enough to make sexual activity a dangerous, you should avoid using Nizagara. Use it cautiously, if you've had a heart attack, stroke, or life-threatening heart irregularities within the past 6 months. Be equally cautious, if you have severe high or low blood pressure, heart failure or unstable angina. In case of cardiac symptoms developing (for example, dizziness, nausea, and chest pain) during sexual activity, do not continue. Tell your doctor about the problem as soon as possible. If you have a condition that might result in long-lasting erections, such as sickle cell anemia, multiple myeloma (a disease of the bone marrow), or leukemia, use Nizagara with caution. Also use cautiously if you have a genital problem or deformity such as Peyronie's disease. If an erection lasts more than 4 hours, seek treatment immediately. Permanent damage and impotence could result. If you have a bleeding disorder, a stomach ulcer, or the inherited eye condition known as retinitis pigmentosa, use Nizagara with caution. Its safety under these circumstances has not been studied yet.