Before the single convention was in full operation, it became apparent that its scope was not sufficiently comprehensive to cover new developments and new problems of drug control. The manufacture of synthetic drugs and the widespread use of amphetamines, barbiturates, hallucinogens, and tranquilizers produced increased pressure for bringing their use under control. In 1971 a Convention on Psychotropic Substances was endorsed by an international conference in Vienna, attended by delegates of seventy-one governments. This convention entered into force in August 1976 when ratified by the required forty states. Loopholes in the enforcement provisions of the 1961 Single Convention on Narcotic Drugs also became apparent, and a conference was called in Geneva in March 1972 to strengthen these provisions. The protocol that was adopted, amending the single convention, came into force in 1975. In June 1987 an International Conference on Drug Abuse and Illicit Trafficking produced a comprehensive operational guide concentrating on reducing the demand for illegal drugs, curbing drug trafficking, and treating addicts. In December 1988 a new Convention on Narcotic Drugs was signed in Vienna, further strengthening the earlier treaties and providing for greater international cooperation in law enforcement and seizure of assets derived from illicit trading in drugs. A United Nations Fund for Drug Abuse Control with modest resources was established in 1971 to assist short-and long-term programs directed against drug abuse. Pledges to this fund increased dramatically in the last 1980s as world attention focused on the enormity and complexity of the drug problem.