A UK panel has proposed vaccinating people—including children—at high risk of addiction. Credit: P Roussel/Images Distribution

Treating cocaine addiction has proven a slow and thorny task for scientists. The best bet, a vaccine, is years away, but it has already raised several ethical questions.

There are an estimated 1.5 million cocaine addicts in the US alone and the related costs run to more than $70 billion per year. But developing drugs to fight cocaine addiction has proven difficult. Most drugs of abuse, such as heroin, stimulate the brain's pleasure circuit by triggering the release of neurotransmitters. But cocaine steps in at the next stage, blocking the reuptake of the neurotransmitters dopamine and serotonin back into the nerve cells.

“Cocaine is an especially intractable problem,” says Donald Landry, an addiction researcher at Columbia University. “It's inherently difficult to block a blocker.”

Recruiting the immune system to block cocaine's effects is one alternative. Cocaine molecules are too small to induce an immune response, but by attaching a cocaine-like molecule to a large protein, researchers found they could coax the immune system into making antibodies to both. The antibodies then bind cocaine in the bloodstream, preventing the drug from entering the brain.

Landry and several others are developing immunization strategies, including vaccines and antibodies, for cocaine addiction. But only one vaccine, licensed to the British biotech company Xenova, is in clinical trials. In Xenova's most recent trial, about 75% of vaccinated addicts were able to abstain from cocaine for three months, the company reported in August, and subjects who relapsed said the high they felt was less potent than before. The company is set to test the vaccine in a bigger phase 2 trial.

Even an effective vaccine would not arrest cocaine addiction, researchers warn. “The word 'vaccine' is accurate, but perhaps unfortunate,” says Paul Pentel, professor of pharmacology at the University of Minnesota. “These are not like vaccines for infectious diseases—it's much more analogous to medication.”

These are not like vaccines for infectious diseases—it's much more analogous to medication. Paul Pentel, University of Minnesota

What's more, using the vaccine is fraught with ethical pitfalls: can an addict truly consent to treatment? Should governments compel high-risk individuals—such as those convicted for drug use—to be vaccinated? Who would decide who is at risk?

“These issues could really tarnish the potential of a medication that could otherwise be very effective for many people,” says Henrick Harwood, who last year chaired an advisory panel convened by the US National Institute on Drug Abuse on the topic.

Creating a framework for discussing those questions in advance could prevent policies that are not rooted in science. In August, a UK government–appointed panel called the Brain Science, Addiction and Drugs Project proposed vaccinating children—potentially even as infants—deemed at risk of using drugs.

Even apart from the ethical dilemmas, such schemes are impractical, researchers say. The vaccine is effective for just three months, requiring four to five doses during that time, notes Landry. “You could immunize all these people,” he says, “but you'd be signing them on for monthly injections for the rest of their lives.”