Many people believe when they see the word natural, its okay to take as much as they want since its ‘found’ in nature. However ‘natural’ products can be very dangerous.
One interaction most people are aware of is with grapefruit, this is seen as a warning on many prescription packets. Grapefruit juice affects how drugs are changed (metabolised) in the body for eventual elimination and can alter the amount of drug in your blood. This can lead to enhanced side effects or lower drug effectiveness. Drugs or toxins are usually broken down (metabolised) so that they can be eliminated from the body, and they pass through the liver. Grapefruit or grapefruit juice can alter enzymes in the body and affect how drugs are changed in the body before they are eliminated. In the case of grapefruit it decreases the activity of the cytochrome P450 3A4 (CYP3A4) enzymes that are responsible for breaking down many drugs and toxins.
Grapefruit contains compounds known as furanocoumarins that block the CYP3A4 enzymes. When grapefruit juice is consumed, the enzyme’s ability to break down the drug for elimination is decreased. Blood levels of the drug may rise, resulting in a risk for new or worsened side effects. Blood levels of the drug may rise, resulting in a risk for new or worsened side effects. One whole fruit or 200 milliliters of grapefruit juice (a bit less than one cup) can block the CYP3A4 enzymes and lead to toxic blood levels of a drug. (1)
Taking medications at a different time from when grapefruit juice is consumed may not prevent the interaction. The effects of grapefruit juice on certain medications can last for over 24 hours. So, even if you take a medicine that is given only once per day, grapefruit and grapefruit juice should still be avoided for the entire treatment period.
Most worryingly Susan sees on some sites that its okay to take certain supplements two hours after any prescription medication or four hours after a medication that says do not take with grapefruit juice, since the supplement uses the same CYP3A4 pathway. There is no evidence to support this, there are a variety of factors that affect how a drug is metabolised (2). Some interactions can inhibit or change the rate its metabolised, while it may not have much effect on you if your hayfever medication is affected, it could have more serious consequences if its your Contraception, Epilepsy or Blood Pressure medication is affected.
Other CYP enzymes are also affected, in particular the following foods often found in supplements can have an interaction:-
- Grape Seed Extract
- Milk Thistle
- St John’s Wort
- CBD oil
The CYP enzyme system is responsible for the metabolism of 90% of prescribed drugs and herbs can induce or inhibit the CYP enzymes. Medication, toxins and hormones are all processed through the liver and some have more than one pass (3), this varies from drug to drug which is why there is no general rule of when it’s safe to take a product that interacts. In particular as you age your liver metabolism slows down so the risk increases (4), quite often more side effects are seen and then more drugs are prescribed to counteract the side effects.
Susan carries out a drug interaction assessment with every client having a full review to ensure that any current self medicated supplements are safe , and any prescribed supplements are suitable.
- https://www.fda.gov/consumers/consumer-updates/grapefruit-juice-and-some-drugs-dont-mix- accessed 24th July 2021
2. https://www.aafp.org/afp/2007/0801/p391.html – accessed 24th July 2021
3. https://www.sciencedirect.com/topics/medicine-and-dentistry/drug-metabolism- accessed 24th July 2021
4. https://academic.oup.com/biomedgerontology/article/67A/2/175/555434- accessed 24th July 2021