It creates a high like marijuana and it was available in stores until this past Saturday.
K2 is a blend of herbs that's been banned in Missouri.
But unlike marijuana, which is easy to identify, enforcing the new law against K2 may be more difficult.
"The interest behind it was that it was a legal form in some people's mind of marijuana," Jefferson City Police spokesperson Doug Shoemaker said.
But unlike the leafy plant, these herbs have a chemical sprayed on them that creates the high.
"So while marijuana is something that can be tested for, I don't think it can translate into the field testing kit that works on the synthetic spray that's put on the K2," Columbia Police spokesperson Jessie Haden said.
There are different types of sprays on different packages of herbal incenses.
Local businesses said the same thing and pointed to a substance similar to K2 called Happy Fun Time herbal incense. It is sprayed with a type synthetic spray that is still legal.
"The law was written so specifically that it outlawed that particular substance that was being sprayed on the plant material. So what people are saying now who want to continue selling something similar is that if we take that same substance and don't use that spray that's been outlawed, but spray something else different on it, now they have a legal product to sell," Haden said.
Haden said that officers will do their best to enforce this law, but it's not going to be easy. She said they'll likely only investigate a violation of the law if they get a complaint about someone using or selling K2.