TORONTO (Reuters) - Canada opposes any U.S. plans to buy Canadian prescription drugs that might threaten the country’s drug supply or raise costs for its own citizens, officials have told U.S. authorities, in a new setback to the Trump administration’s efforts to tackle high drug prices, according to documents obtained by Reuters.

FILE PHOTO: A pharmacist counts prescription drugs at the at the CentreTown Pharmacy in Ottawa, Ontario, Canada, June 12, 2019. REUTERS/Chris Wattie

Canadian opposition is a problem for U.S. lawmakers, who have argued they can lower sky-high prescription drug prices by approving imports from Canada, where prices are lower.

At least ten U.S. states, including Florida, have passed or proposed laws to allow such imports, but actual shipments would not be legal without federal approval. The U.S. Health and Human Services secretary said last week the government was looking into ways to import cheaper prescription drugs from overseas.

“Canada does not support actions that could adversely affect the supply of prescription drugs in Canada and potentially raise costs of prescription drugs for Canadians,” reads an April briefing for Canadian officials obtained under freedom of information laws.

The talking points, prepared by Canada’s foreign ministry for use by Canadian officials who speak with U.S. officials, cite research suggesting shipments to the United States could cause shortages in Canada.

Health Canada confirmed the government’s position has not changed since the talking points were prepared. The ministry said officials have “made Canada’s position clear” to both federal and state officials in the United States and it stood ready to “take action to ensure Canadians have uninterrupted access to the prescription drugs they need.”

U.S. drugmakers, keen to protect profits in the United States, their most important market where prices are generally much higher, have also argued against imports, saying they would put the safety of the U.S. drug supply at risk. Health Canada says the Canadian drug supply is safe.

The documents instruct Canadian officials to say that “importing drugs from Canada is probably not your silver bullet.” It suggests noting that “there are other solutions” and offering to share the ways Canada keeps healthcare costs low.

The issue may pose a fresh challenge to Canada’s relationship with U.S. President Donald Trump, while disruptions in the drug market would be an unwelcome headache for Prime Minister Justin Trudeau’s government, especially ahead of Canada’s October election.

In 2005, an earlier Canadian government promised a bill that would restrict drug exports in response to similar U.S. proposals, but never followed through.

The Trump administration has promised to lower drug prices, but it has failed to push through several initiatives, including forcing drugmakers to disclose prices in TV ads and overhauling the system of drug discounts.

U.S. Democrats see Trump as increasingly vulnerable to criticism on healthcare costs. U.S. presidential contender Bernie Sanders has offered several bills and amendments that would allow drug imports, while Minnesota Senator Amy Klobuchar recently announced a drug price plan that would include letting patients order drugs from countries like Canada.

Sanders is set to join a group of U.S. patients traveling to Windsor, Ontario, to buy cheap insulin later this month.

The documents say the U.S. proposals have not been detailed enough to properly assess impact, but cite a study from 2010 which estimated that if 10% of U.S. prescriptions were filled from Canada, the drug supply would run out in 224 days.

They also note there are already barriers to shipping drugs from Canada to the United States. For example, many purchase agreements forbid the re-export of drugs.

Most of the entities that regulate Canadian pharmacists forbid filling prescriptions written by foreign doctors, but some Canadian pharmacies do ship across the border. The U.S. Food and Drug Administration does not generally block small-scale imports for personal use.

Innovative Medicines Canada, which represents drugmakers including the major U.S. manufacturers, said it is concerned about the import proposals, and raised the issue with Health Canada.

“Canada cannot supply medicines and vaccines to a market ten times larger than its own population without jeopardizing Canadian supplies and causing shortages,” the organization said in a statement.