Michael L. Wenzinger, MD

 

Ongoing efforts to understand the impact of cocaine on the brain and on behavior have gained considerable momentum over the past few decades. It was only 30 years ago when cocaine was widely considered both safe and nonaddicting – “the champagne” of drugs.¹ Progress has been steady since the cocaine-dopamine depletion theory was proposed, and ultimately supported by functional and PET imaging.^2,3

Additional discoveries promise further insights into the neuroscience of addiction, pleasure, and mood. While cocaine use, abuse, and dependence might seem relatively quiescent, compared with the scourge of opiate-related deaths and addiction, it remains a public health concern – and now is the second-leading cause of drug deaths. Cocaine cultivation, smuggling, use, and the number of first-time users are all escalating.⁴

These developments suggest that cocaine problems might get much worse and beg an important question: Will new research give us insight into better solutions?

What the neuroscience shows

As discussed, we already know quite a bit about the neuroscience behind cocaine addiction. The positron emission tomography studies conducted by Nora D. Volkow, MD, and her associates have shown long-lasting changes in abstinent cocaine addicts. Specifically, their findings clearly demonstrated that cocaine changes the brain and depletes dopamine-rich areas. Furthermore, dopamine recovery is negligible after months of abstinence.⁵

However, large gaps in our understanding remain. The realm of epigenetic study and protein expression behind abuse will be key in bridging our understanding of phenotype to genotype. A recent article by Eric J. Nestler, MD, PhD, and his research team, published in the Journal of Biological Psychiatry and titled “Cocaine self-administration alters transcriptome-wide responses in the brain’s reward circuitry,” offers exciting new insights (Biol Psychiatry. 2018 Apr. doi: 10.1016/jbiopsych.2018.04.009).

The study, led by Deena M. Walker, PhD, offers perhaps the most complete illumination to date of the genetic and epigenetic changes seen in the brain after cocaine self-administration and application.

Dr. Walker and her associates used a mouse model and sorted them into one of several groups. One group examined self-administered acute cocaine exposure only, with the mice immediately harvested thereafter. Two longer-term groups included one that had cocaine exposure with prolonged (30-day) withdrawal followed by context re-exposure (context re-exposure defined as being placed back in the special chamber and lighting they first received cocaine in) and another that had a cocaine exposure with prolonged withdrawal followed by both context and cocaine re-exposure.

The researchers also ran a parallel set of control groups substituting saline for cocaine with otherwise identical durations of observation and context re-exposure. Reward-related brain regions were harvested from each subject and examined with RNA-sequencing analysis to investigate the full genomic/transcriptomic profile of each. Pairwise comparison of the various experimental groups against the control groups (for example, the theoretical baseline of genetic expression in a non–cocaine-exposed brain) uncovered telling patterns, which the investigators aptly described as a comprehensive picture of transcriptome-wide change cocaine causes within the reward circuit.

The novel and creative approach used by Dr. Walker and her associates allowed them to uncover a wealth of clinically significant findings. Much could be said about their spotlighting of specific gene/protein targets for potential future pharmacological therapies toward cocaine treatment – an area that is indeed in sore need of invention. While we have highly efficacious medications for overdose and chronic treatment of opiate abuse, the landscape of treatment options for cocaine is far bleaker and shrouded in theory. With that in mind, perhaps the most salient take-home point is the evidence that cocaine, even after one exposure/withdrawal event, causes a dramatic rewiring in the very way genes are expressed across the reward circuit. The researchers found large shifts in the patterns of genetic transcription, unique and specific to discrete regions of the examined brain tissue, such as the ventral tegmental area, ventral hippocampus, and basolateral amygdala.

More interestingly, similar patterns of these genetic alternations were observed based on the exact history of the cocaine exposure. Dr. Walker and her associates concluded that the withdrawal phase and context re-exposure appear to be crucial components in the re-sculpting of the transcriptomic profile of the reward circuity.

The brain is unprepared by evolution for the reinforcing and reorganizing effects of cocaine. Clinicians, too, have learned that cocaine is addicting and can quickly replace drives such as food, water, sex, and survival. These new data from Dr. Nestler’s team reinforce the importance of prevention. In addition, they are reminders to physicians that cocaine causes changes in brain and behavior that are persistent and not necessarily reversible. Patterns of transcriptomic change are alarming enough and have only recent begun to be fleshed out, but patterns of global substance use trends suggest that we need to begin cocaine prevention activities.
 

 

Is another cocaine epidemic inevitable?

The late David F. Musto, MD, who was revered as both expert medical historian and physician at Yale University, New Haven, Conn., offered perhaps the most poignant observation in this regard: He argued that almost every opiate epidemic seems to transition into a psychostimulant epidemic.⁶ Experts have been looking at cocaine and methamphetamine as a way to try to understand the current opioid epidemic. Indeed, the Centers for Disease Control and Prevention’s most recent report on emerging trends in cocaine use shows numerous, concerning upticks in several realms germane to a possible emerging epidemic. One of the more upstream concerns is a gigantic spike in the shear production of coca leaves and cocaine thought to be occurring in Colombia (the principal source of cocaine in the United States). Current U.S. government estimates based on seizure rates from 2016 indicate that Colombia is producing about 910 metric tons of export quality cocaine. That represents a large increase from the 670-ton estimate the year before and the 325-ton estimate the year before that.

Similarly, a sharp rise in cocaine-related deaths, an approximate 52% increase, has been charted from 2015 to 2016. This finding is likely related to the growing presence of adulterants, such as fentanyl and carfentanil, found in seized cocaine samples. However, a rise in first-time cocaine users in the past year, which, according to the National Survey on Drug Use and Health, is up by about 12% (1.1 million people) in the 2015-2016 period, shows that the danger of cocaine-related deaths might not lie solely in adulteration but also increases in use. These signals might herald a grim return of cocaine to the center stage of public health, a development that would be an encore of the crack cocaine epidemic experienced throughout the 1980s and early 1990s.

All the above findings support cocaine as an agent of swift and massive change to our reward systems that might be poised to again surge across the United States at epidemic levels. Given this insight into just how extensively it rewires brains and the unfortunate truth that direct pharmacotherapy treatments remain mostly theoretical, it is evident that the best course of action is simply to keep cocaine from ever reaching the brain in the first place. Prevention does work, and these findings underline the importance of that message. Direct psychoeducation, awareness programs, and deterrence are the best defense we can offer to our patients at this time. In addition to these tried and true techniques, fascinating new models of prevention for cocaine abuse also are in development: vaccines. Synthesized by binding cocaine to inert proteins, these vaccines are designed to prevent addiction by training the immune system to bind cocaine and thus prevent it from crossing the blood brain barrier.⁷ Currently approved for clinical study in humans, these might offer a game-changing new method in the prevention of substance abuse.

 

In summary, continued research has enriched us with a deeper appreciation of just how profoundly cocaine, even after a single exposure, rewires the brain. Some people might have a cavalier attitude about drugs and even use terms such as experimentation to describe teen use, but cocaine is not cannabis. Not only initial cocaine self-administration, but also withdrawal and context of use (a bathroom, a bar table, a countertop) all serve to debase the natural transcriptome balance of the brain’s reward system. Our knowledge of what exactly contributes to the path of the cocaine addiction has grown, but options for how to treat cocaine overdose and addiction remain slim. This is particularly concerning, as history and data indicate a likelihood that a cocaine epidemic might come on the heels of the opiate epidemic. Now more than ever we need to emphasize the importance of preventing cocaine use – and continue to develop new interventions.
 

Dr. Wenzinger is a clinical fellow, PGY-4, in the department of child and adolescent psychiatry at St. Louis Children’s Hospital. Dr. Gold is the 17th Distinguished Alumni Professor at the University of Florida, Gainesville, and professor of psychiatry (adjunct) at Washington University in St. Louis. He also serves as chairman of the scientific advisory boards for RiverMend Health.

 

References

1. Yale J Biol Med. 1988 Mar-Apr;61(2):149-55.

2. Neurosci Biobehav Rev. 1985 Fall;9(3):469-77.

3. Am J Psychiatry. 1990;147(6):719-24.

4. DEA Museum. “A New Look at Old and Not So Old Drugs: A 2018 Update on Cocaine.” Drug Enforcement Administration. Retrieved from https://deamuseum.org/lecture-series/new-look-old-not-old-drugs-2018-update-cocaine.

5. J Addict Dis. 1996;15(4):55-71.

6. The American Disease: Origins of Narcotic Control (New York: Oxford University Press, 1999).

7. Br J Clin Pharmacol. 2014 Feb;77(2):368-74.

 

Ongoing efforts to understand the impact of cocaine on the brain and on behavior have gained considerable momentum over the past few decades. It was only 30 years ago when cocaine was widely considered both safe and nonaddicting – “the champagne” of drugs.¹ Progress has been steady since the cocaine-dopamine depletion theory was proposed, and ultimately supported by functional and PET imaging.^2,3

Additional discoveries promise further insights into the neuroscience of addiction, pleasure, and mood. While cocaine use, abuse, and dependence might seem relatively quiescent, compared with the scourge of opiate-related deaths and addiction, it remains a public health concern – and now is the second-leading cause of drug deaths. Cocaine cultivation, smuggling, use, and the number of first-time users are all escalating.⁴

These developments suggest that cocaine problems might get much worse and beg an important question: Will new research give us insight into better solutions?

What the neuroscience shows

As discussed, we already know quite a bit about the neuroscience behind cocaine addiction. The positron emission tomography studies conducted by Nora D. Volkow, MD, and her associates have shown long-lasting changes in abstinent cocaine addicts. Specifically, their findings clearly demonstrated that cocaine changes the brain and depletes dopamine-rich areas. Furthermore, dopamine recovery is negligible after months of abstinence.⁵

However, large gaps in our understanding remain. The realm of epigenetic study and protein expression behind abuse will be key in bridging our understanding of phenotype to genotype. A recent article by Eric J. Nestler, MD, PhD, and his research team, published in the Journal of Biological Psychiatry and titled “Cocaine self-administration alters transcriptome-wide responses in the brain’s reward circuitry,” offers exciting new insights (Biol Psychiatry. 2018 Apr. doi: 10.1016/jbiopsych.2018.04.009).

The study, led by Deena M. Walker, PhD, offers perhaps the most complete illumination to date of the genetic and epigenetic changes seen in the brain after cocaine self-administration and application.

Dr. Walker and her associates used a mouse model and sorted them into one of several groups. One group examined self-administered acute cocaine exposure only, with the mice immediately harvested thereafter. Two longer-term groups included one that had cocaine exposure with prolonged (30-day) withdrawal followed by context re-exposure (context re-exposure defined as being placed back in the special chamber and lighting they first received cocaine in) and another that had a cocaine exposure with prolonged withdrawal followed by both context and cocaine re-exposure.

The researchers also ran a parallel set of control groups substituting saline for cocaine with otherwise identical durations of observation and context re-exposure. Reward-related brain regions were harvested from each subject and examined with RNA-sequencing analysis to investigate the full genomic/transcriptomic profile of each. Pairwise comparison of the various experimental groups against the control groups (for example, the theoretical baseline of genetic expression in a non–cocaine-exposed brain) uncovered telling patterns, which the investigators aptly described as a comprehensive picture of transcriptome-wide change cocaine causes within the reward circuit.

The novel and creative approach used by Dr. Walker and her associates allowed them to uncover a wealth of clinically significant findings. Much could be said about their spotlighting of specific gene/protein targets for potential future pharmacological therapies toward cocaine treatment – an area that is indeed in sore need of invention. While we have highly efficacious medications for overdose and chronic treatment of opiate abuse, the landscape of treatment options for cocaine is far bleaker and shrouded in theory. With that in mind, perhaps the most salient take-home point is the evidence that cocaine, even after one exposure/withdrawal event, causes a dramatic rewiring in the very way genes are expressed across the reward circuit. The researchers found large shifts in the patterns of genetic transcription, unique and specific to discrete regions of the examined brain tissue, such as the ventral tegmental area, ventral hippocampus, and basolateral amygdala.

More interestingly, similar patterns of these genetic alternations were observed based on the exact history of the cocaine exposure. Dr. Walker and her associates concluded that the withdrawal phase and context re-exposure appear to be crucial components in the re-sculpting of the transcriptomic profile of the reward circuity.

The brain is unprepared by evolution for the reinforcing and reorganizing effects of cocaine. Clinicians, too, have learned that cocaine is addicting and can quickly replace drives such as food, water, sex, and survival. These new data from Dr. Nestler’s team reinforce the importance of prevention. In addition, they are reminders to physicians that cocaine causes changes in brain and behavior that are persistent and not necessarily reversible. Patterns of transcriptomic change are alarming enough and have only recent begun to be fleshed out, but patterns of global substance use trends suggest that we need to begin cocaine prevention activities.
 

 

Is another cocaine epidemic inevitable?

The late David F. Musto, MD, who was revered as both expert medical historian and physician at Yale University, New Haven, Conn., offered perhaps the most poignant observation in this regard: He argued that almost every opiate epidemic seems to transition into a psychostimulant epidemic.⁶ Experts have been looking at cocaine and methamphetamine as a way to try to understand the current opioid epidemic. Indeed, the Centers for Disease Control and Prevention’s most recent report on emerging trends in cocaine use shows numerous, concerning upticks in several realms germane to a possible emerging epidemic. One of the more upstream concerns is a gigantic spike in the shear production of coca leaves and cocaine thought to be occurring in Colombia (the principal source of cocaine in the United States). Current U.S. government estimates based on seizure rates from 2016 indicate that Colombia is producing about 910 metric tons of export quality cocaine. That represents a large increase from the 670-ton estimate the year before and the 325-ton estimate the year before that.

Similarly, a sharp rise in cocaine-related deaths, an approximate 52% increase, has been charted from 2015 to 2016. This finding is likely related to the growing presence of adulterants, such as fentanyl and carfentanil, found in seized cocaine samples. However, a rise in first-time cocaine users in the past year, which, according to the National Survey on Drug Use and Health, is up by about 12% (1.1 million people) in the 2015-2016 period, shows that the danger of cocaine-related deaths might not lie solely in adulteration but also increases in use. These signals might herald a grim return of cocaine to the center stage of public health, a development that would be an encore of the crack cocaine epidemic experienced throughout the 1980s and early 1990s.

All the above findings support cocaine as an agent of swift and massive change to our reward systems that might be poised to again surge across the United States at epidemic levels. Given this insight into just how extensively it rewires brains and the unfortunate truth that direct pharmacotherapy treatments remain mostly theoretical, it is evident that the best course of action is simply to keep cocaine from ever reaching the brain in the first place. Prevention does work, and these findings underline the importance of that message. Direct psychoeducation, awareness programs, and deterrence are the best defense we can offer to our patients at this time. In addition to these tried and true techniques, fascinating new models of prevention for cocaine abuse also are in development: vaccines. Synthesized by binding cocaine to inert proteins, these vaccines are designed to prevent addiction by training the immune system to bind cocaine and thus prevent it from crossing the blood brain barrier.⁷ Currently approved for clinical study in humans, these might offer a game-changing new method in the prevention of substance abuse.

 

In summary, continued research has enriched us with a deeper appreciation of just how profoundly cocaine, even after a single exposure, rewires the brain. Some people might have a cavalier attitude about drugs and even use terms such as experimentation to describe teen use, but cocaine is not cannabis. Not only initial cocaine self-administration, but also withdrawal and context of use (a bathroom, a bar table, a countertop) all serve to debase the natural transcriptome balance of the brain’s reward system. Our knowledge of what exactly contributes to the path of the cocaine addiction has grown, but options for how to treat cocaine overdose and addiction remain slim. This is particularly concerning, as history and data indicate a likelihood that a cocaine epidemic might come on the heels of the opiate epidemic. Now more than ever we need to emphasize the importance of preventing cocaine use – and continue to develop new interventions.
 

Dr. Wenzinger is a clinical fellow, PGY-4, in the department of child and adolescent psychiatry at St. Louis Children’s Hospital. Dr. Gold is the 17th Distinguished Alumni Professor at the University of Florida, Gainesville, and professor of psychiatry (adjunct) at Washington University in St. Louis. He also serves as chairman of the scientific advisory boards for RiverMend Health.

 

References

1. Yale J Biol Med. 1988 Mar-Apr;61(2):149-55.

2. Neurosci Biobehav Rev. 1985 Fall;9(3):469-77.

3. Am J Psychiatry. 1990;147(6):719-24.

4. DEA Museum. “A New Look at Old and Not So Old Drugs: A 2018 Update on Cocaine.” Drug Enforcement Administration. Retrieved from https://deamuseum.org/lecture-series/new-look-old-not-old-drugs-2018-update-cocaine.

5. J Addict Dis. 1996;15(4):55-71.

6. The American Disease: Origins of Narcotic Control (New York: Oxford University Press, 1999).

7. Br J Clin Pharmacol. 2014 Feb;77(2):368-74.

 

Ongoing efforts to understand the impact of cocaine on the brain and on behavior have gained considerable momentum over the past few decades. It was only 30 years ago when cocaine was widely considered both safe and nonaddicting – “the champagne” of drugs.¹ Progress has been steady since the cocaine-dopamine depletion theory was proposed, and ultimately supported by functional and PET imaging.^2,3

Additional discoveries promise further insights into the neuroscience of addiction, pleasure, and mood. While cocaine use, abuse, and dependence might seem relatively quiescent, compared with the scourge of opiate-related deaths and addiction, it remains a public health concern – and now is the second-leading cause of drug deaths. Cocaine cultivation, smuggling, use, and the number of first-time users are all escalating.⁴

These developments suggest that cocaine problems might get much worse and beg an important question: Will new research give us insight into better solutions?

What the neuroscience shows

As discussed, we already know quite a bit about the neuroscience behind cocaine addiction. The positron emission tomography studies conducted by Nora D. Volkow, MD, and her associates have shown long-lasting changes in abstinent cocaine addicts. Specifically, their findings clearly demonstrated that cocaine changes the brain and depletes dopamine-rich areas. Furthermore, dopamine recovery is negligible after months of abstinence.⁵

However, large gaps in our understanding remain. The realm of epigenetic study and protein expression behind abuse will be key in bridging our understanding of phenotype to genotype. A recent article by Eric J. Nestler, MD, PhD, and his research team, published in the Journal of Biological Psychiatry and titled “Cocaine self-administration alters transcriptome-wide responses in the brain’s reward circuitry,” offers exciting new insights (Biol Psychiatry. 2018 Apr. doi: 10.1016/jbiopsych.2018.04.009).

The study, led by Deena M. Walker, PhD, offers perhaps the most complete illumination to date of the genetic and epigenetic changes seen in the brain after cocaine self-administration and application.

Dr. Walker and her associates used a mouse model and sorted them into one of several groups. One group examined self-administered acute cocaine exposure only, with the mice immediately harvested thereafter. Two longer-term groups included one that had cocaine exposure with prolonged (30-day) withdrawal followed by context re-exposure (context re-exposure defined as being placed back in the special chamber and lighting they first received cocaine in) and another that had a cocaine exposure with prolonged withdrawal followed by both context and cocaine re-exposure.

The researchers also ran a parallel set of control groups substituting saline for cocaine with otherwise identical durations of observation and context re-exposure. Reward-related brain regions were harvested from each subject and examined with RNA-sequencing analysis to investigate the full genomic/transcriptomic profile of each. Pairwise comparison of the various experimental groups against the control groups (for example, the theoretical baseline of genetic expression in a non–cocaine-exposed brain) uncovered telling patterns, which the investigators aptly described as a comprehensive picture of transcriptome-wide change cocaine causes within the reward circuit.

The novel and creative approach used by Dr. Walker and her associates allowed them to uncover a wealth of clinically significant findings. Much could be said about their spotlighting of specific gene/protein targets for potential future pharmacological therapies toward cocaine treatment – an area that is indeed in sore need of invention. While we have highly efficacious medications for overdose and chronic treatment of opiate abuse, the landscape of treatment options for cocaine is far bleaker and shrouded in theory. With that in mind, perhaps the most salient take-home point is the evidence that cocaine, even after one exposure/withdrawal event, causes a dramatic rewiring in the very way genes are expressed across the reward circuit. The researchers found large shifts in the patterns of genetic transcription, unique and specific to discrete regions of the examined brain tissue, such as the ventral tegmental area, ventral hippocampus, and basolateral amygdala.

More interestingly, similar patterns of these genetic alternations were observed based on the exact history of the cocaine exposure. Dr. Walker and her associates concluded that the withdrawal phase and context re-exposure appear to be crucial components in the re-sculpting of the transcriptomic profile of the reward circuity.

The brain is unprepared by evolution for the reinforcing and reorganizing effects of cocaine. Clinicians, too, have learned that cocaine is addicting and can quickly replace drives such as food, water, sex, and survival. These new data from Dr. Nestler’s team reinforce the importance of prevention. In addition, they are reminders to physicians that cocaine causes changes in brain and behavior that are persistent and not necessarily reversible. Patterns of transcriptomic change are alarming enough and have only recent begun to be fleshed out, but patterns of global substance use trends suggest that we need to begin cocaine prevention activities.
 

 

Is another cocaine epidemic inevitable?

The late David F. Musto, MD, who was revered as both expert medical historian and physician at Yale University, New Haven, Conn., offered perhaps the most poignant observation in this regard: He argued that almost every opiate epidemic seems to transition into a psychostimulant epidemic.⁶ Experts have been looking at cocaine and methamphetamine as a way to try to understand the current opioid epidemic. Indeed, the Centers for Disease Control and Prevention’s most recent report on emerging trends in cocaine use shows numerous, concerning upticks in several realms germane to a possible emerging epidemic. One of the more upstream concerns is a gigantic spike in the shear production of coca leaves and cocaine thought to be occurring in Colombia (the principal source of cocaine in the United States). Current U.S. government estimates based on seizure rates from 2016 indicate that Colombia is producing about 910 metric tons of export quality cocaine. That represents a large increase from the 670-ton estimate the year before and the 325-ton estimate the year before that.

Similarly, a sharp rise in cocaine-related deaths, an approximate 52% increase, has been charted from 2015 to 2016. This finding is likely related to the growing presence of adulterants, such as fentanyl and carfentanil, found in seized cocaine samples. However, a rise in first-time cocaine users in the past year, which, according to the National Survey on Drug Use and Health, is up by about 12% (1.1 million people) in the 2015-2016 period, shows that the danger of cocaine-related deaths might not lie solely in adulteration but also increases in use. These signals might herald a grim return of cocaine to the center stage of public health, a development that would be an encore of the crack cocaine epidemic experienced throughout the 1980s and early 1990s.

All the above findings support cocaine as an agent of swift and massive change to our reward systems that might be poised to again surge across the United States at epidemic levels. Given this insight into just how extensively it rewires brains and the unfortunate truth that direct pharmacotherapy treatments remain mostly theoretical, it is evident that the best course of action is simply to keep cocaine from ever reaching the brain in the first place. Prevention does work, and these findings underline the importance of that message. Direct psychoeducation, awareness programs, and deterrence are the best defense we can offer to our patients at this time. In addition to these tried and true techniques, fascinating new models of prevention for cocaine abuse also are in development: vaccines. Synthesized by binding cocaine to inert proteins, these vaccines are designed to prevent addiction by training the immune system to bind cocaine and thus prevent it from crossing the blood brain barrier.⁷ Currently approved for clinical study in humans, these might offer a game-changing new method in the prevention of substance abuse.

 

In summary, continued research has enriched us with a deeper appreciation of just how profoundly cocaine, even after a single exposure, rewires the brain. Some people might have a cavalier attitude about drugs and even use terms such as experimentation to describe teen use, but cocaine is not cannabis. Not only initial cocaine self-administration, but also withdrawal and context of use (a bathroom, a bar table, a countertop) all serve to debase the natural transcriptome balance of the brain’s reward system. Our knowledge of what exactly contributes to the path of the cocaine addiction has grown, but options for how to treat cocaine overdose and addiction remain slim. This is particularly concerning, as history and data indicate a likelihood that a cocaine epidemic might come on the heels of the opiate epidemic. Now more than ever we need to emphasize the importance of preventing cocaine use – and continue to develop new interventions.
 

Dr. Wenzinger is a clinical fellow, PGY-4, in the department of child and adolescent psychiatry at St. Louis Children’s Hospital. Dr. Gold is the 17th Distinguished Alumni Professor at the University of Florida, Gainesville, and professor of psychiatry (adjunct) at Washington University in St. Louis. He also serves as chairman of the scientific advisory boards for RiverMend Health.

 

References

1. Yale J Biol Med. 1988 Mar-Apr;61(2):149-55.

2. Neurosci Biobehav Rev. 1985 Fall;9(3):469-77.

3. Am J Psychiatry. 1990;147(6):719-24.

4. DEA Museum. “A New Look at Old and Not So Old Drugs: A 2018 Update on Cocaine.” Drug Enforcement Administration. Retrieved from https://deamuseum.org/lecture-series/new-look-old-not-old-drugs-2018-update-cocaine.

5. J Addict Dis. 1996;15(4):55-71.

6. The American Disease: Origins of Narcotic Control (New York: Oxford University Press, 1999).

7. Br J Clin Pharmacol. 2014 Feb;77(2):368-74.