This couldn't backfire, could it?... Vaccine against drug addiction edition

The New Zealand Herald reported today:

A New Zealand scientist is exploring a new vaccine for drug addiction, which would teach our immune system to reject specific drugs before they could trigger highs.

Researchers have been trying, unsuccessfully, to create such an intervention since the 1970s.

Dr Benjamin Compton believed the failures didn't owe to the concept itself, but to the design of the actual vaccines...

Vaccines were one of the most cost-effective and powerful health interventions available, Compton said, and he believed it should be possible to vaccinate against drug addiction...

Compton would initially test his vaccine on mice, and, if he could prove the concept worked, it could be revolutionary.

"This technology will be really helpful for those addicts who want to break free of their addiction. Should that person come into contact with the drug, a vaccine will ensure there is no reward from the drug-taking behaviour."

I don't know about you, but I can immediately see a potential problem with this solution. You might argue that drug addiction is itself a problem. I'd agree, provided the addiction causes some other dysfunction in the addict's life, which causes harm to themselves or to others. One obvious harm to the user themselves is the risk of drug overdose.

As a very simple explanation, drug addiction arises because the drug stimulates the reward centre of the brain, causing a 'high'. The high feels good, and the addict continues to use the drug in order to experience the high they get from it. Over time though, drug users develop some tolerance to the drug, and so they might need to use a higher dose of the drug in order to achieve the same high.

Compton's vaccine would interrupt this process by preventing the drug from stimulating the brain's reward centre, thereby preventing the drug user from achieving the high. It seems like a clear solution to drug addiction, so why would it be a problem?

Let's assume that the vaccine is to be administered to current drug addicts, in order to help cure their addiction. If you interrupt the chemical process that leads the drug to stimulate the reward centre in the brain, then some current addicts who are treated with the vaccine would respond by consuming more of the drug, in order to try to get their high. And if the chemical process that focuses on the reward centre in the brain is different from the chemical process that results in toxic drug overdoses, there is a very real risk that the vaccine could lead to more drug overdoses (or at least, it substantially raises the risk of overdose for those addicts who are treated with it).

Alternatively, perhaps the vaccine is designed to prevent addiction in the first place. Exactly who, among non-drug-users, is going to agree to be vaccinated against drug addiction?

So, the vaccine might reduce drug addiction, but come at the cost of more drug overdoses. You solve one problem, but I would worry that you are creating a problem that is potentially much worse. Sometimes unintended consequences are entirely foreseeable.