include antipsychotics for treating hallucinations and delusions, and antidepressants for treating depression. The role of tobacco smoking in the causation of cancer and other diseases was proven during the 1950s (see British Doctors Study). New methods for cancer treatment, including chemotherapy, radiation therapy, and immunotherapy, were developed. As a result, cancer could often be cured or placed in remission. The development of blood typing and blood banking made blood transfusion safe and widely available. The invention and development of immunosuppressive drugs and tissue typing made organ and tissue transplantation a clinical reality. New methods for heart surgery were developed, including pacemakers and artificial hearts. Cocaine and heroin were widely illegalized after being found to be addictive and destructive. Psychoactive drugs such as LSD and MDMA were discovered and subsequently prohibited in many countries. Prohibition of drugs caused a growth in the black market drug industry, and expanded enforcement led to a larger prison population in some countries. Contraceptive drugs were developed, which reduced population growth rates in industrialized countries, as well as decreased the taboo of premarital sex throughout many western countries. The development of medical insulin during the 1920s helped raise the life expectancy of diabetics to three times of what it had been earlier. Vaccines, hygiene and clean water improved health and decreased mortality rates, especially among infants and the young. Notable diseases An influenza pandemic, Spanish Flu, killed anywhere from 17 to 100 million people between 1918 and 1919. A new viral disease, called the Human Immunodeficiency Virus, or HIV, arose in Africa and subsequently killed millions of people throughout the world. HIV leads to a syndrome called Acquired Immunodeficiency Syndrome, or AIDS. Treatments for HIV remained inaccessible to many people living with AIDS and HIV in developing countries, and a cure has yet to be discovered. Because of increased life spans, the prevalence of cancer, Alzheimer's disease, Parkinson's disease, and other diseases of old age increased slightly. Changes in food production, along with sedentary lifestyles due to labor-saving devices and the increase in home entertainment, contributed to an "epidemic" of obesity, at first in the rich countries, but by the end of the 20th century spreading to the developing world. Energy and the environment Fossil fuels and nuclear power were the dominant forms of energy sources. Widespread use of petroleum in industry—both as a chemical precursor to plastics and as a fuel for the automobile and