New studies strengthen evidence that drug addiction is a disease of the brain; substitution therapy necessary

Two scientific lectures presented at the Eighteenth International AIDS Conference in Vienna last week, demonstrated that drug use in and of itself is linked to increased rates of HIV transmission, giving support for evidence that substitution therapy programmes could help to stem the HIV epidemic.

Currently, ten million injecting drug users (IDUs) are living with the virus worldwide. While needle sharing is a strong predictor of HIV seroconversion, non-injecting drug users also experience increased rates of transmission when compared to the general population. This is a result of drugs’ impact on brain chemistry and function, as they diminish inhibitory responses and therefore lead to riskier behaviour.

Nora Volkow of the US National Institute on Drug Abuse, or NIDA, noted, “the prevalence rates of substance abusers are in many instances equivalent whether they inject or don’t inject.”

Charles O’Brien from the University of Pennsylvania agreed, stating, “Even oral drugs greatly increase the risk of being… positive.” As such, combating HIV transmission among non-injecting drug users “is even more complex than addressing just injecting drug use, [in which] you only have to address contaminated equipment”, said Volkow.

Discussing alcohol, cocaine, heroin and methamphetamine use, Volkow noted that many drugs increase sexual desire and impulsivity while decreasing the function of the inhibitory and controlling systems of the brain, with acute and chronic drug use affecting the prefrontal cortex. Brain and behaviour changes can often last several years after use is discontinued. 

Addiction is a “chronic disease”, said Volkow. People take the drug “not because the individual [wants to], but because they have lost their ability to control”.

According to O’Brien, the notion that drug addiction is a disease of the brain is not a novel concept. “We have very good evidence [that addiction] is governed in large measure by our genes. A lot of people who are addicts are not guilty of anything that the rest of us don’t do, like experimenting with drugs,” he said.

While “it should not be any surprise that sexual behaviours increase when intoxicated”, the pinpointing of changing brain behaviour and chemistry is a relatively new phenomenon, according to Volkow. Such data demonstrate “that you actually can very specifically identify the biochemical changes in the brain that lead us to understand the disruptive behaviour”, she explained.

In addition to increasing the risk of HIV transmission, some psychoactive drugs actually exacerbate the neurotoxic effects of HIV. Volkow explained that this “combination of two very different vectors… collide to disrupt [brain function] even further”.

Such findings provide further support for substitution replacement therapy. “If you don’t treat addiction, the likelihood of [an] individual being infected by HIV becomes higher,” said Volkow. Studies have shown that full methadone treatment reduces the rate of HIV seroconversion from 20 to 2% over 18 months. “We need to treat the drug users if we want to treat HIV,” noted Volkow. “In fact, preventing drug use is treating HIV.”

Methadone replacement therapy, which is the most effective treatment available today, is “much more than harm reduction”, said O’Brien. “Methadone is rehabilitation.”

The therapy can be used far beyond simply aiding in initially quitting drugs, with many former addicts “staying on methadone for the rest of their lives”, said O’Brien. Addiction needs to be treated “like high blood pressure and diabetes”, O’Brien noted. “It doesn’t just go away because people have been treated,” he said. According to O’Brien, long-term treatment “doesn’t interfere with normal behaviour” such as attending school or holding down a steady job.

Several new substitution therapies are on the market or in trials, including a vaccine that would block the effects of drugs on the brain, therefore decreasing the likelihood of an individual becoming addicted. Until new technologies become available, O’Brien encourages current treatment to become more “accessible, acceptable, and affordable”.

In addition to diminishing drug use, treating and preventing new infections among drug users is also a central component to tackling the HIV epidemic.

Professor Julio Montaner, former president of the International AIDS Society and a champion of HAART as prevention, described HAART use among IDUs in Vancouver’s Downtown Eastside neighborhood, which is home to the highest rates of drug use and HIV in Canada.

Noting that high HIV viral load is actually more predictive of HIV transmission than needle sharing, Montaner’s study showed that by treating HIV-positive IDUs, community viral load decreased and HIV incidence plummeted, despite the fact that drug use and other behaviours such as unprotected sex persisted. As HAART was further expanded throughout the study, the number of new infections continued to decrease.

While Montaner noted that increasing the coverage of prevention methods such as behavioural interventions is necessary, increased treatment is also essential to lessening a community’s HIV burden. “This is not about medicalising prevention, this is about treating people who need treatment [as well as] strengthening traditional ways of preventing HIV including education, change in behaviour, harm reduction, and embracing new strategies and technologies… if and when they become available,” he said.