Old drugs with minor variations, and therefore new patents, are behind the massive growth in spending on prescription medicines in developed countries, but do not offer substantial improvements over cheaper generic drugs, according to scientists at the University of British Columbia in Canada.

Known as “me-too” drugs, these medicines on average cost twice the price of the original brand-name drugs they are based on, and four times that of generic versions of the original drug.

The study, published this week by the British Medical Journal, reports that spending on drugs doubled in Canada between 1996 and 2003. The scientists broke down the expenditure into different groups of medicines to see which were responsible for the jump.

They found that me-too drugs accounted for 44 percent of use and 63 percent of expenditures by 2003. In contrast, the use and expenditure on vintage brand-name drugs and generics shrank over the seven-year period.

“In British Columbia, [80 percent] of the increase in drug expenditure between 1996 and 2003 was explained by the use of new, patented drug products that did not offer substantial improvements on less expensive alternatives available before 1990,” said the paper.

“Given that the list of top 20 drugs in global sales includes newly patented versions of drugs in long established categories… me-too drugs probably dominate spending trends in most developed countries,” added the researchers.

In particular, the researchers point to drugs in several classes, including angiotensin-converting enzyme (ACE) inhibitors, which treat high blood pressure; statins, which lower levels of “bad” cholesterol; anti-depressants known as selective serotonin reuptake inhibitors; and proton pump inhibitors, which are used to treat and prevent stomach ulcers.