Generic Drug Interactions
Sildenafil Citrate
Sildenafil Citrate comes with the most notorious reactions, when combined with nitrates. If under any other medication, ensure that your medicine does not have Nitrate in its chemical composition. Chest or heart patients are prescribed medicines with Nitrate. To name a few: nitroglycerin such as: Nitrostat, Nitrolingual, Nitro-Dur, Nitro-Bid and such others. Also, isosorbide dinitrate (Dilatrate-SR, Isordil, Sorbitrate), isosorbide mononitrate (Imdur, ISMO, Monoket), amyl nitrate or nitrite (poppers) are some other nitrate forms that could be a part of your medicine. When nitrate combines with Sildenafil Citrate, it causes serious low blood pressure with symptoms such as: dizziness, fainting, heart stroke.
Organic nitrates are a strict no-no, when consuming Tadalafil. This results in life-threatening reactions such as hypotension or extreme low blood pressure. Medicines with nitrate can only be consumed after at least 48 hours of Tadalafil intake, under doctor’s guidance. Other sex drugs such as amyl nitrate, a form of organic nitrate should be avoided within the same time frame.
The below mentioned chemical names and medicines (including these chemicals) increase the levels of Tadalafil in your body, due to a reaction caused. This should be avoided by consuming lower levels of Tadalafil to cure ED. 
  • Erythromycin (E-Mycin, Eryc, Ery-Tab, PCE, Pediazole, Ilosone)
  • Ketoconazole (Nizoral, Extina, Xolegel, Kuric)
  • Itraconazole (Sporanox)
  • Indinavir (Crixivan)
  • Ritonavir (Norvir). 
Check if you are consuming medicines containing nitrate or any nitrate form composition such as: 
  • Nitroglycerin
  • Isosorbide dinitrate (Isordil)
  • Isosorbide mononitrate (Imdur, Ismo, Monoket)
  • Nitroglycerin (Nitro-Dur, Transderm-Nitro)
The aforementioned chemicals (with the medicines in which these chemicals are found) are mainly prescribed to heart patients suffering especially from Angina. The undesirable reaction caused by the coming together of Nitrates and Tadalafil is that it results in increase of heart rate, causing heart attack and very low blood pressure. In case of emergency or bad reaction caused, notify your doctor about Tadalafil recent intake. 
The drug interactions listed are general. It is difficult to always conclude the drug reactions, when combined with the other. This is because of the difference in body types and yet many other variables:
  • Grape fruit juice is known to create bad reactions in patients consuming ED drugs that are composed of Vardenafil. This is because the reaction is a cause for increase of plasma concentrations of oral drugs, which are substrates of the CYP450 3A4 isoenzyme.
  • Alcohol (Ethanol) reaction with Vardenafil risks very low blood pressure level - increase of hypotension, dizziness, head ache and increase in heart rate