The International Narcotics Control Board (INCB) also pointed to a rise in the use of so-called date rape drugs, as sexual abusers try to get around more rigorous controls with substances not banned by international drugs laws.
The INCB said several high-profile celebrity deaths, such as pop star Michael Jackson last year, had focused attention on prescription drug abuse.
In the United States, abuse of prescription drugs is now the second most important drug abuse issue after cannabis, it said, with 6.2 million people hooked on them in 2008.
Abuse of such drugs has been spreading over the world in recent years, said Hamid Ghodse, director of the International Center for Drug Policy at St George's University in London and one of the report's authors. It needs to be tackled urgently.
Ghodse said it was difficult to get comprehensive data on the abuse of pharmaceuticals, which he described as a hidden problem, but in Germany, for example, an estimated 1.4 to 1.9 million people were addicted to prescription drugs.
In Canada, an estimated 1 to 3 percent of the population abuses prescription opioids, and in several European countries -- such as France, Italy, Lithuania and Poland -- between 10 and 18 percent of students use sedatives or tranquilizers without a prescription.
Illegal internet pharmacies, which sell stolen, diverted and counterfeited medicines around the world, are a major supply source for prescription drugs abusers, the INCB said, and it urged governments to monitor them closely or shut them down.
The INCB also said it wanted to raise the alarm about new substances becoming the drugs of choice for sexual abusers.
Drugs like ketamine and gamma-Butyrolactone (GBL), which are not controlled under international drug conventions, are replacing Rohypnol, which was in the past so commonly used in sexual assault that it was called the date-rape drug.
Ghodse said stricter control measures by governments and the pharmaceutical industry had helped curb use of Rohypnol, or flunitrazepam, which is now rarely used in attacks, but newer drugs were easier to get hold of and abuse.
Since in many countries these drugs are easily available, they frequently fall into criminal hands, he told reporters.
INCB president Sevil Atasoy said greater efforts were needed in preventing drug abuse of all kinds as a means of cutting off demand and breaking the supply chain. Organized and powerful criminal networks were constantly finding new processes, routes and substances to keep drug manufacturing operations alive.
Preventing drug abuse is a crucial area of demand reduction, she wrote in the report.