Opium has been used and produced for thousands of years. During this time, the source plant has been changed and adapted. The methods of processing the plant, and extracting substance and consuming it also have changed. The medicinal use of poppies for pain relief dates back to ancient times, but widespread use in patent medicines or as a recreational drug has occurred only in the last few centuries. Drug prohibition laws in most countries were introduced in the 20th century. Today the opium crop is worth in excess of $400 million legally and $7 billion illegally, after processing. Opium has caused many wars in China, such as the Opium Wars, because of heavy addiction to the drug. People who become addicted to opium become dull, lazy, and even sleepy. Opium itself is a very harmful and addictive ingredient and comes in many other forms of illegal drugs; including Heroin and/or Diamorphine. 