Your doctor will probably tell you not to take tadalafil if you are taking street drugs containing nitrates. Generic versions of sildenafil, vardenafil and tadalafil are available. Other uses for this medicine This medication may be prescribed for other uses; ask your doctor or pharmacist for more information. Both Cialis and Viagra are effective at these doses. There is also the option to take Cialis as needed. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra.Oral medications, like Viagra and Cialis, which require a prescription and are commonly used to treat ED, can take 30 minutes to take effect, she adds. Injections take less time to work, but they. Cialis works relatively quickly. You may start to feel its effects after about 30 it can take up to 2 hours for its full effects to kick in. By comparison, Viagra begins to work within 30 minutes; its maximum effects . We have good news for you: generic Cialis, used to treat erectile dysfunction (ED)and enlarged prostates, just hit pharmacies. Prices for the generic, known as tadalafil, are more than 50% less than those of brand-name Cialis. As more men are able to afford tadalafil and treat their ED, it’s likely that many will have questions.