Drug Interactions
Capsaicin increases the time blood needs to clot, and when taken with anticoagulant medicines like warfarin, the effect of the medicine may be intensified.
Toxicity
Acute oral LD50 values were determined to be 97.4 mg/kg and 118.8 mg/kg in female and male mice, respectively, and 148.1 mg/kg and 161.2 mg/kg in female and male rats, respectively.[1]
Metabolism
CYP2C9 was identified as the primary enzyme responsible for converting capsaicin into 16-hydroxy-capsaicin and 16,17-dehydro-capsaicin. CYP2C19 may also contribute to the formation of 16-hydroxy-capsaicin.[4]
Effects On Cytochrome P450 Enzymes
Effects in Humans In Vivo
None have been reported.
Effects in Rats In Vivo
Capsaicin was found to induce CYP3A4 in rats.[2]
In rats multiple doses of capsaicin and dihydrocapsaicin also induced CYP2E1.[3]
Effects In Vitro
The tests discussed in this section are in vitro tests. It's important to note that in many cases these kinds of enzyme based tests show different results from those seen in real human test subjects.
At concentrations occurring after ingestion of chili peppers or topical administration of a high-concentration patch, capsaicin did not cause any direct inhibition of any Cytochrome P450 enzymes. Inhibition was only observed at much higher concentrations.[5]
An in vitro test performed on human liver microsomes found that capsaicin and dihydrocapsaicin moderately inhibited the Cytochrome P450 enzymes CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4 and CYP3A5. IC50 values ranged from 4.4 to 61.8 μM.[3]
Another vitro test showed that capsaicin inhibited CYP1A2, CYP2C9 and CYP2C19, with IC50 values of 2.1, 2.0 and 3.2 mcM, respectively. Capsaicin also appeared to inhibit CYP2B6, CYP2D6, CYP3A4 and CYP3A4 directly with IC50 values of 24, 18, 38 and 12 mcM, respectively. The same test showed that capsaicin did not induce CYP1A2, CYP2C9, CYP2C19, CYP2B6, CYP2D6, CYP3A4 or CYP3A4.[4]
Another in vitro test found that capsaicin did not induce CYP2E1 but instead induced CYP1A2 by 8.6%.[5]