The Opium Law (or Opiumwet in Dutch) is the section of the Dutch law which covers nearly all psychotropic drugs. Most non-psychotropic, but prescription-only drugs are covered by the Medicine Act, the most well known exception being Ketamine which is covered by the Medicine Act.
In 1911, the First International Opium Conference took place in The Hague, where agreements were made about the trade in opium; this initiated the introduction of the Opium Law, which took place 7 years later. In 1919, the first Opium Law (later known as List I of the Opium Law) was introduced, and on 12 May 1928 the second Opium Law (later known as List II of the Opium Law) was introduced. The first Opium Law was created to regulate drugs with a high addiction or abuse factor, or that are physically harmful. As the name indicates the main reason for introduction was to regulate the Opium trade and later to control various other addictive drugs like morphine, cocaine, heroin, barbiturates, amphetamines and several decades later, benzodiazapines, which were used both medically and recreationally.
Except for the addition of new drugs to List I and II of the Opium Law, the Opium Law remained unchanged until 1976. After the rise of a new youth culture which revolved much around the use of drugs like cannabis and LSD, and with hashish being openly used, a change of law was needed by the government, to properly control all drugs, but with a clear definition between drugs with an unacceptable degree of addictiveness or physical harm (known as hard drugs), and drugs with an acceptable degree of addictiveness or physical harm (known as soft drugs). In 1976 these changes officially took effect, and the Opium Law was edited to include the changes in the law. In the same year, a decision was made by the Dutch government discontinue prosecuting cannabis and hashish offenses, provided the person did not sell hard drugs, did not advertise and carried less than a specified maximum amount of cannabis or hashish.