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Understanding potential drug to drug interactions

Just about all chemical compounds, including prescription, over-the-counter and herbal formulations and some foods can potentially interact with each other. And cannabis-based products are no different.

About 60% of pharmaceutical drugs are metabolised through a pathway of more than 50 enzymes called the cytochrome P450 (CYP450) pathway. The role of this pathway is to process and eliminate toxins in the liver.

Certain substances can increase or decrease how fast other medications or substances are metabolised through the liver.

Cannabidiol can inhibit the CYP450 system of enzymes, meaning it will take longer to metabolise other medications. This can lead to higher doses in your blood stream and unwanted side effects; or signs of toxicity, at lower than expected doses, requiring close monitoring and adjustment of both compounds if needed.

Caution needs to be exercised with blood thinners such as warfarin; anti-hypertensive medications especially when taking THC; sedatives like alcohol and benzodiazepines; narcotics like codeine and some antiepileptic medications (AED).

Conversely, some drugs are may decrease the bioavailability of THC by increasing the rate at which the THC is metabolised in the body. This means higher amounts of THC may be needed to gain the same therapeutic benefit. This can significantly increase the cost of the medicine.

Before commencing any form of cannabinoid-based therapies it is worthwhile to check for any potential drug to drug interactions not only with anti-epileptic medications but any other prescription, over-the-counter, herbal or supplemental products.

Researchers at the University of Alabama USA studied interactions between CBD and anti-epileptic medications. They found significant changes in serum levels for clobazam (Frisium), rufinamide (Banzel), topiramate (Topamax) and eslicarbazepine (Zebinix or ESL) in the presence of CBD. They also noted abnormal liver function tests when CBD was taken with Valproate (Epilim).

Gaston TE, Bebin EM, Cutter GR, Lui Y, Szaflarski JP, 2017, Interactions between cannabidiol and commonly used antiepileptic drugs, Epilepsia, Vol. 58, No. 9, p.p. 1586-92.

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