Generic Viagra contains Sildenafil which may interact with other medicines. The interactions may be minor to serious. Nitrates and other medications for heart problems should not be combined with Sildenafil.
Other oral PDE-5 inhibitors such as avanafil (Stendra), tadalafil (Cialis) or vardenafil (Levitra) should not be mixed with Sildenafil. If a patient uses other methods to enhance erectile dysfunction, he should not use Viagra concomitantly. drug interactions
Certain medicines may interact with Viagra including medicines for depression treatment, antibiotics, antifungal medications, drugs to treat autoimmune states and AIDs treatments. Before applying Viagra online a patient should inform his doctor if he uses any of the following:
•    bosentan (Tracleer);
•    cimetidine (Tagamet, Tagamet HB);
•    conivaptan (Vaprisol);
•    imatinib (Gleevec);
•    isoniazid (for treating tuberculosis);
•    nefazodone;
•    clarithromycin (Biaxin), erythromycin, or telithromycin (;
•    antifungal medication such as itraconazole (Sporanox), ketoconazole (Nizoral), or voriconazole (Vfend);
•    alfuzosin (Uroxatral), doxazosin (Cardura), prazosin (Minipress), terazosin (Hytrin), silodosin (Rapaflo), tamsulosin (Flomax, Jalyn);
•    diltiazem, nicardipine (Cardene), quinidine (Quin-G), or verapamil;
•    boceprevir (Victrelis) or telaprevir (Incivek); or
•    atazanavir (Reyataz), darunavir (Prezista), fosamprenavir (Lexiva), indinavir (Crixivan), nelfinavir (Viracept), ritonavir (Kaletra, Norvir), saquinavir (Fortovase), or tipranavir (Aptivus).
Other medical products should also be taken into consideration when a person decides to start Viagra for ED.