Those with psychiatric disorders comprise 44% of cigarette sales in the United States. Since the 1950s, researchers funded by the tobacco industry have been studying the connection between psychiatric illnesses and smoking. The self-medication theory was proposed in the 1980s by a tobacco-industry-affiliated researcher who claimed that nicotine may help people with schizophrenia in a “therapeutic” way. Some non-industry-affiliated researchers have contended that this self-medication hypothesis has promoted smoking to a vulnerable audience with psychiatric conditions.