Adrian Carter | neurobiologist and ethicist, Monash University

In a nutshell: Adrian Carter discusses the thorny issues surrounding neuro-medication and culpability.

A former politician was recently convicted of having sex with an underage girl in Tasmania, Australia.

The defendant pleaded guilty to the offence. Nonetheless, he was given a wholly-suspended 10-month sentence.

The man’s defence lawyers successfully argued that he had a compulsive sexual disorder brought on by the drugs he was taking to treat the debilitating tremors and mobility problems of Parkinson’s disease.

The judge accepted that “if not for the medication” the man would not have committed the offences, that his criminal sexual behaviours were caused by his Parkinson’s medication. The man was also considered at low risk of repeating the offences because he had stopped taking the medication.

Similar rulings have occurred in the UK and France.

The drugs in question are the“dopamine agonists”, such as pramipexole and ropinirole. Dopamine agonists are used to make up for the loss of brain cells that release the neurotransmitter, dopamine; a hallmark of Parkinson’s. For many patients, they are the most effective medication.

But do these medications cause new behaviours, or simply unmask latent tendencies that some people have?

And if a person does have a latent desire to behave in a criminal or harmful fashion, but has successfully resisted until taking the medicine, are they more or less responsible for their behaviour?

These important, unresolved questions need to be addressed by legal, clinical and ethical experts, and wider society.

One in 5 patients taking dopamine agonists develop some type of impulsive and compulsivebehaviours . These include pathological gambling, hypersexuality, and compulsive eating and shopping. More positively, some people taking dopamine agonists develop artistic interests and become intensely creative.

To give you a sense of what compulsive behaviour looks like, the Tasmanian politician visited sex workers on over 506 occasions in less than two years. Other’s affected by the medication have gambled over $100,000 and lost their homes and businesses.

The timing of these behaviours suggest that the drugs are a critical causal factor. They usually start soon after a person starts taking dopamine agonists, or has a large increase in their dose, and most often disappear when the medication is stopped or the dose significantly reduced.

On the other hand, the fact that only a minority — 1 in 5 — of people who take dopamine agonists develop these behaviours shows that the medicines are not the whole story.

Our group at the Monash Clinical and Imaging Neuroscience laboratory are investigating other possible contributory factors. One line of enquiry is finding out how people who take the medicine, and then develop harmful compulsive behaviours, feel about their actions. Do they identify with their new behaviour and feel good about it? Or do they feel that it has been imposed upon them by an external source, by the drug?

You can find out more about issues like this here.

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The Essentials

  • medicines can have profound effects on our thoughts and behaviour
  • judges and juries are grappling with how to deal with crimes triggered by these medicines
  • we don’t know how people who commit antisocial behaviour in response to medicines feel – is their behaviour alien or unnerving to them? or do they feel that’s its ok?