Psychological factors like stress, depression, or anxiety can also contribute. Finding an online ED provider can feel overwhelming. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. This is important for your overall health and safety, as certain medications can negatively interact with each other or cause existing conditions to worsen. Sildenafil may cause side effects. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise.The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 minutes to 4 hours before sexual activity. And you. Here are some details on sildenafil: Drug class: phosphodiesterase type 5 (PDE5) inhibitor Drug forms: oral tablet, liquid suspension, intravenous (IV) bolus injection Brand-name . Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP.