Two anti-cocaine efforts in Colombia, funded by American taxpayers, were not cost-effective, according to an analysis by two economists. The interventions “are inefficient and socially costly ways of reducing drug consumption,” they conclude.

Between 2000 and 2008, the United States spent $4.3 billion on efforts to eradicate cocaine in Colombia, The Washington Post reports. According to economists from MIT and Colombia’s Universidad de los Andes, it cost the U.S. government $940,000 to eliminate a single kilogram of cocaine from the domestic market through herbicide spraying in Colombia. Eliminating a single kilogram through interdiction efforts to block cocaine transit routes and seize shipments of cocaine cost $175,000.

The report considered the tactics that coca growers and drug traffickers use to respond to enforcement efforts, such as increasing production and changing trade routes, the article notes.

The findings are published in the Journal of Economic Behavior and Organization.

Reducing cocaine consumption through drug treatment strategies would cost between $12,500 and $68,705, the researchers found in an earlier analysis.

The program to eliminate cocaine production in Colombia did not appear to have significant impact on cocaine use patterns in the United States, according to the article. Between 2000 and 2008, cocaine use patterns were essentially flat, while the price per gram purchased in the United States fell slightly, from $205.67 to $182.75.

The researchers said cocaine growers became more efficient in response to eradication efforts, significantly increasing crop yields through better growing and farming practices. As Colombia intensified enforcement efforts, other countries, such as Peru and Bolivia, increased their cocaine production.

Jonathan Caulkins, a drug policy expert at Carnegie Mellon University, said the social costs of cocaine should be taken into account when analyzing money spent on interdiction efforts. These include harm to people using cocaine, as well as the people around them, and costs relating to enforcement.