The Complexities of Comorbidity in Addiction

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Comorbidity is a phenomenon common in drug abusers. The term refers to multiple medical conditions in the same patient. Estimates are that up to 60% of addicts have another, underlying psychiatric problem, with depression ranking highly. When two dysfunctions in the brain overlap, it is very difficult to separate out how the problems interact. This makes treating comorbidity a challenge. So, for example, is depression leading someone to alcohol or drugs – or does the addiction cycle lead to worsening depression instead?

Scientists have been looking at the question for some time. Treatment specialists are familiar with comorbidity, and they watch for symptoms of mental disease during detox and rehab. Now, in a paper to be published in Molecular Psychiatry (abstract here) researchers have shown just how complex the interaction between substance abuse and mental disease can be.

Schizophrenia and Amphetamines

The study used patients diagnosed with schizophrenia who also used amphetamines and compared their brain scans to healthy volunteers. During the study, the schizophrenics weren’t on other medications.

Schizophrenia is noted as a condition where increased dopamine in one part of the brain causes symptoms. Since addiction to amphetamines lowers background dopamine release (requiring more of the drug to get the same high), the expectation is that schizophrenics would get fewer symptoms if they used and natural dopamine release was impaired by the drug. However, the opposite is known to be the case.

How is it that lowering dopamine release can increase schizophrenic symptoms caused by dopamine? Dopamine release is lowered in one part of the brain (the reward centers), just as it is in all amphetamine addicts. At the same time, sensitivity to available dopamine goes up in another (the part responsible for psychiatric symptoms). The same neurotransmitter (dopamine) was being handled differently in different parts of the brain.

Mystery solved, but we once again have an illustration that biology and brain chemistry have many tricks. Many more mysteries remain.

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