What should Fluoxetine and Paroxetine be avoided with?

Fluoxetine and Paroxetine, both selective serotonin reuptake inhibitors (SSRIs), are known to interact with various medications. Their interaction with Tamoxifen and Codeine is significant due to the role of the cytochrome P450 enzyme system in drug metabolism.

Tamoxifen is a medication commonly used for hormone receptor-positive breast cancer. It is metabolized into its active form, endoxifen, primarily by the CYP2D6 enzyme. Both Fluoxetine and Paroxetine are strong inhibitors of this enzyme, which means they can reduce the effectiveness of Tamoxifen, potentially compromising its therapeutic efficacy in cancer treatment. Consequently, this can lead to worsened outcomes in patients relying on Tamoxifen for managing their cancer.

Codeine, on the other hand, is an opioid that is also metabolized by CYP2D6 into its active form, morphine. If Fluoxetine or Paroxetine are taken with Codeine, they can inhibit the conversion process, resulting in decreased analgesic effects and increased risk of inadequate pain control for patients using Codeine as part of their treatment regimen.

In summary, the combination of Fluoxetine and Paroxetine with Tamoxifen and Codeine should be avoided due to the potential for significant drug interactions that can