The drugs we offer through VidaRx are either generic Viagra or generic Cialis. These drugs work very similar to one another with one main difference. Cialis works for 36 hours, while Viagra works for 4. This means if you are aroused during those times your penis will become harder than usual. The best way to take these drugs is 1 hour prior to sex with a full glass of water. If you have an erection longer than 4 hours seek emergency medical care. Common side effects include: headache or stuffy nose. You also CANNOT take this medication with any medicine for chest pain such as nitroglycerin. For more detailed safety information click here