Dirk Hanson’s The Chemical Carousel is an in-depth survey and discussion of the pharmacology of addiction. It focuses around one central point: a certain percentage of the population is susceptible to addictions, while others can use addictive drugs occasionally and never get addicted. Because of the physiological, psychological, and sociological problems addiction leads to, we need to understand the brain changes that occur during addiction, withdrawal, and relapse. The study of the pharmacological action of many psychoactive substances is ongoing, as is research into the pharmacology of addiction itself. This detailed generalist account is probably the most comprehensive single work on the topic for the lay reader.

Initially, as I read through this fairly substantive tome I had doubts about the author’s general view of addiction. Hanson clearly views addiction as a brain disorder, one to which a particular percentage of the population, say 10% or so, is susceptible largely, Hanson argues, by virtue of genetics. While the other 90% of the public can occasionally go on a methamphetamine binge or experiment with heroin without becoming addicted, this minority will become addicted. This is because of tremendous individual variability in brain chemistry. While I still have my doubts about whether a pharmacological model explains every facet of addiction and recovery, Hanson does an outstanding job of explaining the various effects of psychoactive substances on neurotransmitters and the reward pathways of the brain. In the end, he also admits that addiction is a complicated phenomenon with sociological and psychological causes as well as physiological ones. Nonetheless, the physiological mechanisms need to be elucidated, and Hanson focuses largely on this.

The heart of the book is a dissection of the effects of various commonly used psychoactive substances on the brain, and a discussion of possible treatment options, including newer pharmaceuticals compounds, that attempt to stem cravings and thus prevent the ubiquitous condition known as relapse. Hanson focuses on substances that are commonly abused and known to be addictive: nicotine, alcohol, stimulants, opiates. He also includes cannabis though considerably less is known about the mechanism of cannabis addiction, and controversy remains over whether cannabis can be really said to be addictive at all. Hanson devotes three long chapters to discussing pharmacological agents used to treat substance abuse, addiction, and craving. Many new drugs either just coming on the market or not yet on the market are discussed.

It is hard to summarize the results, since Hanson paints a complex picture that includes findings from hundreds if not thousands of research studies. Research on these topics is ongoing and increasing. Though not a light read, The Chemical Carousel is an important and comprehensive look at the contemporary science of the addicted brain.