Virginia Gov. Bob Mc­Don­nell (R) signed into law Wednesday a bill banning dried herbs sprayed with chemicals — known as synthetic marijuana, K2 or spice.

The bill passed the General Assembly unanimously last month. It will take effect immediately.

“I am pleased that Virginia has now joined at least 15 other states that have taken action to protect our citizens, particularly our young people, from these dangerous designer drugs,” said. Sen Mark Herring (D-Loudoun).

Clemson University chemistry professor John Huffman developed the ingredients in spice in 1995 while researching the effect of cannabinoids, the active compounds found in marijuana. The compound has never been approved by the Food and Drug Administration for human consumption.

Spice is supposed to provide effects similar to those of marijuana — sleepiness, relaxation and lowered blood pressure — but some users have reported anxiety, a racing heartbeat, nausea and vomiting. There have been some cases of hallucinations, seizures, unconsciousness and suicide.

Spice has been sold in the United States since 2006 but only made its way to Virginia in late 2009 or early 2010. Authorities say it caught on with teenagers and young adults who wanted to get high without risking the legal consequences of marijuana. Spice doesn’t show up on drug screens.

Tuesday, The Post reported that the operators of three shops and two gas station convenience stores in the District received written notice that they risk having business assets seized and forfeited under federal law if they sell spice.