If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately. My first experience was at the other corner pharmacy not my preferred CVS I did have insurance through my employer. All PDE5 inhibitors, including Viagra and Cialis, require a valid prescription regardless of the pharmacy or provider. To use the oral liquid: Shake the bottle well for at least 10 seconds before each use. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects.Maria Hudson. 4 hrs. ago. Anna Nelson. 6 hrs. ago. David Muldon. 8 hrs. ago. Headache, flushing, and upset stomach are common Viagra side effects. These effects are usually mild and often resolve on their own. While rare, Viagra can cause an erection that lasts longer than 4 hours (priapism). This can result in permanent damage if left untreated. Vision changes are also possible.  · The effects may be increased because of slower removal of the medicine from the body. Leukemia (blood related cancer) or. Multiple myeloma (blood related cancer) or. Sickle-cell anemia (blood disorder)—Sildenafil should be used with caution in these patients as problems with prolonged erection of the penis may occur.