People taking nitrates like nitroglycerin Nitrostat or isosorbide mononitrate Imdur should not take PDE5 inhibitors, as doing so could result in a dangerous drop in blood pressure. Brand names Why is this medication prescribed? These PDE5 inhibitors may cause headache, flushing, drop in blood pressure, or other adverse effects. Refills: See if you can set up automatic refills or order as needed. All PDE5 inhibitors, including Viagra and Cialis, require a valid prescription regardless of the pharmacy or provider. Those with pre-existing conditions should always consult a healthcare provider before taking new medications or supplements. It’s available in 25 mg, 50 mg, and mg tablets and lasts up to 18 hours.Best Chewable Pill: BlueChew. Best Long-Term Care: K Health. Best Low Cost: GoodRx. Fastest Delivery: Blink Health.: Sesame. Sign Up Now. Key Specs. Cost: . If you have these symptoms, stop taking VIAGRA and contact a doctor right away. have or have had heart problems such as a heart attack, irregular heartbeat, angina, chest pain, narrowing of the aortic valve, or heart failure. have low blood pressure, or high blood pressure that is not controlled. Sildenafil generic Revatio and Viagra Used for Pulmonary Hypertension and Erectile Dysfunction MORE expand_more Check your prescription Prescription 20mg sildenafil .