The US Medicaid programme is paying far more than necessary for medicines and not offering patients the most effective treatments available, a new study suggests.

Researchers from the University of California, San Francisco (UCSF) compared Medicaid's Preferred Drug Lists in 40 US states against the World Health Organisation (WHO) Essential Medicines List for 2009, and found that the drugs which Medicaid pays for automatically (ie, without prior authorisation) vary widely from state to state, with little in the way of consistent protocols or rationales - including safety, cost or effectiveness - for their selection.

The US has 51 different lists of medications that are paid for by Medicaid, and only a third of these drugs appear consistently on the various state lists, according to the authors, who publish their findings in the American Journal of Public Health. The programme is ignoring international evidence-based lists of safe and effective medications, but by using a more consistent approach to deciding which drugs will be covered, it could save significant money and also provide safer and more effective medications for patients, they add.

Medicaid, the US state/federal health programme for people on low incomes, currently serves around 60 million citizens - around 20% of the US population - and this number is set to rise under the Obama Administration's health reforms.

The UCSF researchers identified 369 medicines in the nine therapeutic classes that had the highest annual Medicaid reimbursements. These drugs included all but six of the 120 products recommended by WHO for these categories, but the use of WHO-list products was inconsistent across the state lists, while another 249 medicines on the states' lists were not recommended by WHO as the most effective and safest treatments.

The 249 medications that only appeared on state lists were also less likely to have generic versions available - only 56% of the state-list drugs did so compared with 76% of those on the WHO list.

"The issue is not that our patients cannot get the WHO-recommended medicines, but that they are receiving a wide variety of other medications that cost more and are not always as effective or safe," said researcher Lisa Bero, a professor at the UCSF School of Pharmacy.

The findings suggest that if states used the WHO lists as a starting point, "it might reduce the number of medicines available to Medicaid patients, but patients could have more confidence that the medicines they receive are effective and safe," she added.

• In 2007, the United Nations (UN) reported that 131 countries out of 151 uses the WHO Essential Medicines List as a basis for their national formulary - the US is not among them.