Viagra generally refers to sildenafil citrate, for that matter, but the general public, or non-professional pharmacy guides, tend to think of it as a type 5 phosphodiesterase inhibitor, a class of drugs for treating erectile dysfunction in men, which are now more commonly known as sildenafil and tadalafil.
Both of these drugs are relatively effective in the treatment of erectile dysfunction and are used in much the same way, usually taken orally about 2 hours before sex.
Sildenafil effect time is relatively short some general drug effect lasts 4-6 hours, and need to use on an empty stomach. Tadalafil, on the other hand, lasts up to 36 hours and is not affected by diet.
This class of drugs can cause adverse reactions such as headache, back pain, indigestion. It is contraindicated for people who are allergic to this class of drugs, patients who are taking any form of nitrates, women and other people.
In general, patients with erectile dysfunction need to go to the hospital to check and clarify the cause of the disease, combined with their own situation, under the guidance of the doctor targeted selection of medication, can not blindly use drugs.