Roundup, one of the most common and widely used weed killer, contains Glyphosate as one of its main ingredients. Glyphosate is a systemic and broad spectrum herbicide which was patented by a U.S. company, Monsanto, in 1970. The chemical name of glyphosate is N-(phosphonomethyl)glycine, and it blocks an enzyme in the plant which is needed for preparing amino acids and proteins, thus, killing the plants within a few days.
After the patent for Monsanto expired in the U.S. in 2000 and outside the U.S. in 1991, many other manufacturers started marketing their own glyphosate products leading to a substantial increase in the sales and global usage.
Since 2013, there was an awareness created about Roundup that it may be connected to some serious medical conditions. This was confirmed in March 2015, when World Health Organization (WHO) announced that there was a probable link between glyphosate and Non-Hodgkin lymphoma and other forms of cancer. It is believed that the manufacturer knew about this linkage and covered its tracks unofficially.