Clinical research specifically examining this drug-drug interaction in human subjects is currently very limited. The potential for an interaction is not chemical, but rather a metabolic complication that occurs inside the body. Combining any two biologically active compounds introduces a level of risk, as each can influence how the other is absorbed, processed, and eliminated. Understanding how the body handles these two substances requires looking closely at the liver’s detoxification machinery.
How the Body Processes Cannabis and Antibiotics Together
The interaction between cannabis and antibiotics is primarily governed by the liver’s Cytochrome P450 (CYP450) enzyme system. This family of enzymes is responsible for metabolizing approximately 70 to 80 percent of all medications currently on the market. Both the primary cannabinoids, Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), and many common antibiotics rely on these same enzymes for their breakdown.
Cannabinoids, particularly CBD, are known to be potent inhibitors of several key CYP450 enzymes, such as CYP3A4 and CYP2C9. When CBD inhibits an enzyme, it occupies the enzyme’s active site, preventing it from processing other substances that also rely on that pathway. Many antibiotics, including the macrolide class (like erythromycin or clarithromycin), are metabolized by these exact same CYP3A4 enzymes.
The result of this competition is a “traffic jam” in the liver’s metabolic pathway. If the cannabinoid slows the enzyme activity, the antibiotic is metabolized more slowly than intended, causing it to linger in the bloodstream. This can lead to a higher-than-expected concentration of the antibiotic, or its active metabolites, circulating in the body over a longer period. Conversely, certain components of cannabis can induce, or speed up, the enzymes, causing the antibiotic to be cleared out too quickly. The final outcome is an unpredictable and altered concentration of one or both drugs, which can compromise treatment safety and efficacy.
Impact on Treatment Efficacy
Altering the metabolism of an antibiotic can significantly compromise its ability to clear an infection. Antibiotics are prescribed with a specific dosing schedule designed to maintain the drug’s concentration within a narrow therapeutic window. This window ensures the level is high enough to exceed the Minimum Inhibitory Concentration (MIC) required to kill the bacteria, but low enough to avoid toxicity.
When cannabis use slows the antibiotic’s breakdown, the concentration becomes unpredictable. This increases the risk of the drug level dropping below the MIC, meaning the antibiotic may only inhibit the bacteria instead of killing it outright. This can prolong the illness, lead to treatment failure, and require switching to a different medication.
Fluctuating drug levels also pose a risk for the development of antibiotic resistance in the pathogen. Exposure to sub-therapeutic concentrations of an antibiotic provides bacteria with an opportunity to survive and develop mechanisms to resist the drug. Any factor that introduces metabolic variability works against the overall goal of rapidly eliminating the infection.
Amplifying Known Side Effects
Elevated drug concentrations resulting from inhibited metabolism directly contribute to an increased risk of side effects. Since the antibiotic is not being cleared from the system efficiently, its toxic effects are more likely to manifest and be amplified. This effect is particularly noticeable with side effects that are common to both antibiotics and cannabis.
Gastrointestinal distress is a prime example, as many antibiotics cause nausea, vomiting, and diarrhea. When combined with cannabis, these gastrointestinal symptoms can be compounded, leading to a far more unpleasant experience. Both substances affect the central nervous system, and the combination can lead to increased symptoms of dizziness, drowsiness, and impaired coordination.
Some antibiotics, particularly macrolides, carry a known risk of affecting heart rhythm, sometimes causing QT prolongation. Since THC can temporarily increase heart rate and blood pressure, combining the two may place additional strain on the cardiovascular system. The severity of these adverse reactions is directly proportional to the unexpectedly high concentration of the antibiotic in the bloodstream.