Generic brand
Generic brands of consumer products (often supermarket goods) are distinguished by the absence of a brand name.
They may be manufactured by less prominent companies, or manufactured on the same production line as a 'named' brand. Generics brands are usually priced below those products sold by supermarkets under their own brand (frequently referred to as "store brands" or "own brands"). Generally they imitate these more expensive brands, competing on price. Generic brand products are often of equal quality as a branded product, however the quality may change suddenly in either direction with no change in the packaging if the supplier for the product changes.
Generic drugs
Patents may prohibit generic brand manufacturing. In the specific case of drugs, new drugs are almost always patented and therefore generic versions of drugs may only be made legally in most of the world when the patents expire. As with other generic products, generic drugs are much cheaper due to both competition and the fact that research and marketing costs do not need to be factored in.
Sildenafil citrate
Sildenafil citrate, sold under the names Viagra, Revatio, Caverta and under various other names, is a drug used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH), developed by the pharmaceutical company Pfizer. Its primary competitors on the market are tadalafil (Cialis), and vardenafil (Levitra).