 When we talk about new psychoactive substances or, in short, NPS, we are referring to necotic or psychotropic drugs that are not under international control. This means that they are not listed in the United Nations conventions of 1961 or 71, the international treaties that state which drugs are under control, such as cocaine, cannabis, heroin, amphetamine, LSD and methamphetamine. Nevertheless, NPS may still be a threat to public health and cause social harms, just like the drugs listed in the conventions. Many NPS mimic the effects of internationally controlled drugs. For example, synthetic cathenones are used as replacements for stimulants such as emphatamine or cocaine and synthetic cannabinoids as replacements for cannabis. NPS can be found in different types of products, such as legal highs, research chemicals, food supplements or designer drugs. And NPS may include medicines. Although NPS are not controlled internationally through the UN conventions, there might be other forms of control. And NPS can be controlled through the national legislation in a country, either by name or as part of a more generic definition based on chemistry or effect. Following a risk assessment by the EMCDDA scientific committee, the Council of the EU may also decide that a substance should be controlled in all the EU member states. Some substances might pass through different levels of control over time. Maffadrone is a good example. It emerged as an NPS in 2007. As problems occurred, more and more European countries started controlling it. And after a risk assessment by the EMCDDA, it was controlled at EU level. Since 2015, it is also controlled internationally in the UN conventions. This is why Maffadrone cannot be considered an NPS anymore. In contrast to this, ketamine has been surfacing as an NPS in the mid-1990s. It is controlled at national level in various countries and was risk assessed by the EMCDDA in 2000. Nevertheless, it is not controlled at EU level or internationally, which is why we still call ketamine an NPS. So to summarize, an NPS may be controlled in some European countries, depending on the national laws in place. It might also be controlled at EU level. If it is internationally controlled, it is not an NPS.