Doxycycline, a widely used antibiotic, might help reduce the addictive effects of drugs like morphine and cocaine, according to new research published in Progress in Neuro-Psychopharmacology and Biological Psychiatry. This finding opens up new possibilities for treating substance use disorders, offering hope for more effective interventions.
Substance use disorders represent a major public health challenge globally. Characterized by the compulsive use of addictive drugs, these disorders lead to severe behavioral and neural changes, posing significant treatment challenges.
Existing treatments are often inadequate, underlining the urgent need for new therapeutic strategies. The researchers embarked on this study to explore the potential of doxycycline, a common antibiotic known for its anti-inflammatory properties, in mitigating the addictive effects of certain drugs.
“Our interest in this topic from the complexity and recurrent nature of substance use disorders, which present a significant public health concern,” said study author Amanda J. Sales, a postdoctoral researcher at the Ribeirão Preto Medical School at the University of São Paulo.
“Despite this, the neurobiology underlying these disorders is not fully understood, with a lack of effective treatments. In addition to being an antibiotic, doxycycline has important anti-inflammatory and neuroprotective properties (at low doses, that use lack antibiotic properties). Since brain immune/inflammatory mechanisms have also been associated with substance use disorders, we decided to verify if this drug could be useful in this condition.”
The study was conducted at the University of São Paulo, where 302 male mice were subjected to a series of experiments to assess the impact of doxycycline on addiction-related behaviors. The mice, housed under standard laboratory conditions, were randomly assigned to different treatment groups, ensuring unbiased results. The research was performed in compliance with ethical guidelines to minimize animal suffering.
The experiments involved administering various doses of doxycycline, morphine, and cocaine to the mice. Two primary tests were used:
- Conditioned Place Preference (CPP): This test measured the mice’s preference for an environment associated with drug exposure. It involved an apparatus with two chambers, each with distinct visual and tactile cues. The time spent by the mice in each compartment before and after drug administration was recorded, providing insights into the drugs’ rewarding effects.
- Locomotor Sensitization: This test assessed the hyperactivity and increased movement induced by cocaine. Mice were observed in an open field arena following drug administration, measuring changes in their locomotor activity.
The researchers found that doxycycline significantly reduced the rewarding effects of morphine in the mice, as shown by their decreased preference for the drug-associated environment. Importantly, it did not affect morphine’s pain-relieving properties.
The antibiotic also attenuated both the development and expression of cocaine-induced addictive behaviors. Interestingly, a single dose of doxycycline before testing was enough to reduce the expression of reward-associated memory related to cocaine. In addition, doxycycline effectively prevented the hyperactive behavior and psychomotor sensitization typically induced by cocaine.
These results suggest that doxycycline could be a valuable tool in treating substance use disorders. The antibiotic’s ability to modulate memory and behavioral responses associated with drug addiction without affecting the primary therapeutic effects of drugs like morphine (for pain relief) is particularly promising.
“It is important that everyone understands substance use disorders as psychiatric illnesses lacking rapid and effective treatments. Nevertheless, several studies, including our own, have investigated into these conditions and potential treatments with greater efficacy,” Sales told PsyPost.
“Our preclinical study showed the effectiveness of an antibiotic in improving behaviors associated with use of abuse drugs. These findings pave the way for potential use of this “old” class of drug in treating substance use disorders. However, more studies are needed because this is an initial study performed in animals.”
Despite these promising results, it’s important to note that the study was conducted exclusively on male mice. This limitation raises questions about the applicability of the findings across different genders. Future research needs to include female subjects to understand any potential sex differences in response to treatment.
Moreover, the exact mechanism by which doxycycline influences addictive behaviors is not fully understood. While the study suggests that the antibiotic’s effect on matrix metalloproteinases (MMPs) – enzymes involved in brain plasticity – could be a key factor, more research is required to confirm this hypothesis and explore other possible mechanisms.
“Our study was the first that investigated the effects of doxycycline on the rewarding and psychomotor responses induced by addictive drugs,” Sales explained. “Although we administered low doses for a short duration in our study, it is crucial to note that the use of antibiotic drugs, including doxycycline, can lead to antibacterial resistance.”
“Moreover, this is a preclinical study conducted in rodents, and until now, no studies using doxycycline have been performed in humans with substance use disorders. Therefore, this is an initial study, and further studies are needed to understand the molecular mechanisms associated with these effects.
“It is very important to conduct further studies investigating the neurobiology of substance use disorders and exploring potentially more effective treatments,” Sales added. “We are actively engaged in this ongoing research.”
The study, “Doxycycline diminishes the rewarding and psychomotor effects induced by morphine and cocaine“, was authored by Amanda J. Sales, Pedro H. Gobira, João F.C. Pedrazzi, João R. Silveira, Elaine Del Bel, Felipe V. Gomes, and Francisco S. Guimarães.
