Seabed's Nectar (Kaitei no mitsu) is the secret ingredient for Slusho! It is highly addictive and seems to affect the human mind if eaten in its raw form. "Discovered on the deep ocean floor, under amazing pressure and extreme cold." The Parasites found on Clover's body have extremely high levels of Seabed's Nectar in their blood, and have been photographed digging into the ocean floor near the site of Chuai Station.
Its official translation is 'Seabed's Nectar' as seen in Vernon's review and Slusho.jp's Distribution Opportunities page. Before this was found, the offered translations were usually incorrect. One of these mistranslations was 'ocean bottom crab'. Another, which persists today, is 'ocean's bottom honey'. While 'ocean bottom's honey' and 'seabed's nectar' may sound like the same thing, there is a significant difference between honey and nectar.
Some time ago, the drink-loving Noriko Yoshida set out to find "the best, most tastiest ingredient", and disappeared on this search (and presumably died). slusho.jp described this as a sea adventure, however it is unknown whether she knew that it would be located underwater beforehand or how it was actually an adventure (if one at all). Years later, Tagruato, an underwater petroleum excavation company, discovered kaitei no mitsu. Its CEO, Noriko's son Ganu Yoshida, then had a dream telling him that this substance was the ingredient his mother had been looking for. This led to the birth of Slusho.
Almost nothing is known about the nature of Seabed's Nectar. It is known that the source seabed's nectar is located in a very cold place (obviously the seabed). It is also known that it must be consumed in "a near-frozen state", and Slusho.jp's Distribution Opportunities section talks about machines being used to preserve its freshness. Keeping it very cold is also mentioned as preserving its freshness, so it would be reasonable to assume that the machines keep the ingredient cold, which it needs to be until consumption. According to the second chapter of Cloverfield/Kishin, this ingredient is heavily implied to be components made of Kishin Aiba, his mother and the monster itself.
Slusho.jp and tagruato.jp's only mentions of Seabed Nectar's effects are that it has "health benefits". Ravaille Research Center's report on Seabed's Nectar mentioned the following effects: Accelerated cell growth, increased strength, increased soft muscle tissue growth, sharper eyesight, better digestion, smoother skin, and a full-body, pleasant sensation that one of our researchers actually described as "a wave of pure happiness".
It has also been implied that it is quite addictive. It has no known side-effects and is quite safe, as it has been approved by the "American Food Association" (presumably referring to the FDA, as there is no AFA and they are the only organization that can approve things for distribution).