 What are drugs? This question seems to be self-evident, but you will soon realize it is more complicated than you thought. When people think about drugs, they usually associate to plants, pills, injections, liquids or powders. But actually these are only the forms in which drugs are used. They don't tell much about what drugs really are and how are they different from other things such as bread or tomato? According to the broad definition, drugs can be everything that change how your body works. Some drugs are psychoactive. That means that they alter how your brain and mind works. They are like keys that fit into special locks in your nerve cells called receptors. This way psychoactive drugs activate or block the release of certain molecules produced by our body, which change our mood, our perception and our behavior. However, there are a whole lot of other things that can change our mood and perception, such as eating foods, falling in love or even riding a bicycle. That's why people can get addicted to certain behaviors or even to people. Drugs can be sorted into different categories according to how they change our mind. Stimulant drugs, such as cocaine or amphetamine, increase our energy and alertness. Depression drugs, such as alcohol or heroin, repress our arousal and stimulation. Psychedelic drugs, such as LSD or mushroom, change the ordinary way how we perceive reality and can trigger mystical experiences. However, the lines are not always clear cut. For example, alcohol can act both as a depressant and a stimulant. What's really important to understand is that even the same drugs can act in very different ways, depending on three factors. Set, setting and dose. Set is your mental and physical condition, your expectations and your mindset. Setting is the environment in which you use drugs, including the people with whom you use drugs. Dose is how much drugs you use. Even one of these factors can make the least harmful substance becoming lethal. For example, water can be toxic if you drink too much. The ancient Greeks knew this. Their word for drug, pharmacos, means post-medicine and poison. It was also the name of a human scapegoat, which was sacrificed to purify the community from its sins. So the meaning of drugs has been ambiguous from the ancient times. Today, most drugs can be used for both medicinal and recreational purposes. For example, cannabis as a medicine can treat sclerosis multiplex, but it can also help you to relax after a hard day. MDMA can be used to treat post-traumatic stress disorder. But when it's used by young people at dance festivals, it's called ecstasy and it's considered a dangerous illegal drug. The molecular structure of Aderal, a medication widely used to treat young people with attention deficit hyperactivity disorder, is very similar to a street drug called ICE, Matan Fatamin, which is an illegal drug and its users are criminalized. So the difference again is not in the molecular structure of drugs, but how we people perceive these drugs and how we use them. Many people think that illegal drugs are more dangerous than legal drugs. But this is not the case. Professor David Nutt and his colleagues assessed the risks of 20 popular illegal and legal substances. They found that some legal substances such as tobacco or alcohol were among the most harmful substances, while some illegal substances such as cannabis or ecstasy were among the least harmful substances. So if it is not about the risks, why some drugs are legal and others are illegal? In the next video, we will tell you the story. Please stay with us on Drug Reporter, follow us on Twitter and on Facebook.