Low Serotonin Levels May Fuel Drug Addiction

It’s well understood that various neurochemicals, particularly dopamine, play crucial roles in drug addiction, but a new study finds that serotonin may also be involved in the development of addiction. The finding has the potential to change how we view and treat addiction. However, the study isn’t perfect, focusing primarily on MDMA (the key ingredient in Ecstasy) and being conducted on rats, so it’s worth finding out more rather than assuming that a revolution in addiction treatment is just around the corner.

MDMA Self-Administration and Serotonin

The study was actually split into two experiments, both of which were conducted on rats. The first study looked at the increases in serotonin and dopamine in response to an injection of MDMA before the rats were given the option of self-administering the drug. The relationship between the increase in serotonin levels and the later choice of self-administering the drug was examined. The second study involved purposefully depleting the serotonin levels in the rats’ brains before they were allowed to self-administer the drug. The researchers compared the impaired rats to non-impaired rats in terms of whether they took the drug through choice and how long it took them to do so.

In other words, the study aimed to look at the impact of pre-existing serotonin levels and responses to MDMA on whether somebody would begin using the drug. The study observed natural responses and the differences in behavior when baseline levels were purposefully lowered. Lead researcher Sarah Bradbury commented, “People develop drug addiction due to changes in specific brain systems following repeated drug use, but not all drug users become addicted.” The research was designed to determine why only some users become addicted.

Serotonin Is Central to the Development of MDMA Addiction

The increase in serotonin following a (forced) dose of MDMA was much lower for the group of rats that later went on to self-administer the drug, but there was no difference in the level of the increase in dopamine between the groups. When the rats’ serotonin levels (but not their dopamine levels) were purposefully depleted, it was found that the serotonin-depleted rats were much more likely to take MDMA through choice. In the depleted group, all of the rats took MDMA, compared to just half of those in the non-depleted group.

Five days after the last self-administration session, dopamine-related behaviors were increased in the depleted group and serotonin-related behaviors were decreased in comparison to the control (non-depleted) group. After two weeks (the time taken for brain serotonin levels to recover), the differences in serotonin behaviors disappeared while dopamine-related behaviors were still more common in the previously serotonin-depleted rats.

Bradbury explained the findings: “The higher the serotonin levels someone has, the less likely [he] will become addicted.” But Bradbury also pointed out that once drug use becomes common, the protective effect of serotonin is diminished and “another brain chemical, dopamine, seems to be the critical determinant of drug addiction during this phase.”

Dopamine, Serotonin and a Treatment for Addiction

Dopamine (the brain’s “reward” chemical) has consistently been identified through extensive research as the crucial component in most addictions, so the finding that serotonin may also play a crucial role is a potentially important one. Serotonin has been widely linked to mood (with a major type of depression medication focusing on the neurotransmitter), so it stands to reason that it would have some part to play in addiction. Additionally, previous studies have found that MDMA use can lead to major serotonin depletion and depression when the drug leaves a person’s system.

Understanding the complex interplay of brain chemicals that leads to the development of addiction gives researchers the hope of developing targeted treatments. Bradbury’s results suggest that if drugs were developed that increased levels of serotonin, these could be used as a preventive measure against drug addiction. However, MDMA and cocaine were the main focus of the research, so while the findings are expected to apply to other drugs, it isn’t a certainty. Finally, as always with animal studies, comparable findings in humans would be needed before such medications could be developed.

Possible New Hope, But With Caveats

Of course, preventing drug addiction isn’t quite the same as treating it. To turn the results of this study into a meaningful decrease in addiction rates, you’d need to identify those with low serotonin levels and then treat them, which would be problematic to say the least. While it’s possible that this could happen in the future, it’s clear that 12-step programs and other psychological approaches will continue to be the mainstay of addiction care for the foreseeable future.