Understanding Food and Drug Interactions

Disclaimer.  I am not a licensed health practitioner.  This is just another post on knowledge and understanding you might wish to acquire in advance of a disaster in case no higher care is available.  As long as our society is functioning, you should leave anything more substantial than applying a Band-Aid to the professionals.  No medication, including those available over the counter, should be taken without consulting a physician.  Information shared here is for educational and entertainment purposes only.  It is not medical advice nor a substitute for licensed medical care.


We've probably all heard about food and drug interactions, but unless they affect us directly we don't pay much attention.  At least, I know I don't.  I've only got so much available memory and I can't waste it on information that doesn't apply to me.

Unfortunately, we've all got to become a lot more aware of the medications and supplements we take, or may take in the future, and research them well now while we have the ability.  TEOTWAWKI is not the time to start wondering if the grapefruits growing in your neighbor's yard are going to interfere with the antibiotics you're taking to treat pneumonia.

There are a few points to understand before delving into specifics.  First, we have drug-drug interactions, where physicians have to make sure that whatever they're prescribing for you doesn't react with whatever you're already on.  Most doctors do a pretty good job of this.  Then there are the food-drug interactions, you know, those foods you better not eat if you're taking certain medications, like no grapefruit anything for those on thyroid medications.  These tend to be pretty commonly understood as well.  Where it gets a little dicey is with the herbal supplement-drug interactions.

Physicians don't tend to do so well in this area right now.  Understandably, they're pressed for time in seeing patients, and that's probably not going to change.  In fact, it may not be any different down the road either, but then doctors won't likely have references to check, even if they're so inclined.  Like the rest of our society, the vast majority of health care providers are not preparedness-minded and do not have hard copies of essential references.  You might be all right if the doctor you see in your new situation is/was an ER physician or family practitioner.  If you're over 60 or pregnant, you might be out of luck.  All those drugs, herbs, and contraindications are just too much to remember for every situation. 

In the case of drug-drug interactions, the medications may inhibit or amplify one or the other or both, or they may have an entirely different effect that neither has on its own.  In the case of using Tylenol in addition to a cold or flu medication that also has acetaminophen in it, there is the risk of overdosing and liver failure.  A commonly known drug-food interaction is that tetracycline should not be taken with milk.  The risk here is not overdose, but on the contrary, that the tetracycline will be 50-90% less effective.  You definitely do not want to be wasting precious antibiotics when the grid goes down.  Herbs also interact with drugs.  Mixing St. John's wort, an extremely common herbal treatment for depression and anxiety, can be deadly when mixed with dextromethorphan, which is often found in OTC cough syrups.  The fact that you're using an herb doesn't mean it's perfectly safe or free of interactions.  Quite the contrary.

Sometimes the effect is to diminish efficacy of a drug.  However, that is not usually the case.  More often, the various drug interactions have an additive effect (1+1=2) or a synergistic effect (1+1=3). This can come in very handy if it's well-understood and studied in advance.  Who wouldn't want to be able to stretch their Percocet supply?  Especially if it could be done with some grapefruit juice or Benadryl?  Co-Q10, a frequently used supplement, has also been implicated in drug-food interactions.

We've all got to research our own medications and any possible interactions they may have with the foods and herbs we will be eating.  Now's definitely the time to do it, and there's no way we should rely on someone else to do it for us.  I can't go into the kind of necessary detail for each drug on the blog.  That' a whole 'nuther blog for someone else to write.  But here are some examples of the kinds of interactions you need to familiarize yourself with.

• Fruit juices.  Grapefruit juice is the most common of the fruit juices to have some kind of drug interaction, and it does so with almost all classes of drugs.  It increases the bioavailability of felodipine, cyclosporine, and midazolam above toxic levels.  It affects fexofenadine and statins like lovastatin.
• Fiber.  High fiber diets may reduce efficacy of statins like Simvastatin and fluvastatin.  Pectin and oat bran reduce the absorption of lovastatin.
• Warfarin.  Eating too many vegetables like broccoli, kale, and Brussels sprouts can interfere with warfarin.  Char-broiled foods decrease warfarin activity, but cooked onions increase warfarin assimilation.  
• Licorice (the herb, not the candy) may affect heart medications and increase blood pressure.  
• Ciprofloxacin absorption is decreased by milk and grapefruit juice.
• Azithromycin absorption is decreased by over 40% if taken with food.  
• Tetracycline should be taken on an empty stomach as well. 
• Acetaminophen absorption is slowed by food, especially pectin (like is found in jam and sometimes yogurt), so for faster pain relief it should be taken on an empty stomach.
• NSAIDS like Advil and Aleve can upset the stomach, so they should be taken with food.
• Ibuprofen absorption is increased when taken with Coca-Cola.
• Theophylline.  High fat diets increase the amount of theophylline in the body; high carbohydrate diets diminish theophylline in the body.  Avoid excess caffeine to reduce the risk of toxicity.  Avoid grapefruit juice.  
• Heartburn medications and alcohol can cause sudden changes in blood pressure and increase the heart rate.
• Antihistamines and motion sickness medications taken together can lead to overdoses. 

If you're going to stockpile a medication, you've got to be aware of the potential interactions.  Actually, you have to be more than aware.  You've got to write them down and keep the information in a place where everyone in your group knows about it and has access to it.  Research it.  Each and every medication, even if you are the only one who uses it. If you've only got a few medications, you can probably do your research online and print up the results.  However, if you've got a lot, or if you've got a larger group of people, you're really going to want some hard copies.  When you see the size of the books, you'll understand why most doctors put them on their devices.  I'm not comfortable with only having electronic access to my references, so I choose books, even if they are big.

Physicians' Desk Reference (PDR) started it all.  It is the authoritative source for information on all prescription drugs.  It includes everything you need to know as well as data from clinical trials.  It's a really big book and probably much more than what you need to have.  The smaller nurses' handbooks will probably be sufficient for most people.  However, if you're really into the medicine, you may want a copy.

PDR for Nonprescription Drugs and Dietary Supplements covers all the OTC pain relievers, cough and cold medications, allergy pills, and topical creams as well as all the vitamins we take to improve our health.

PDR for Nutritional Supplements addresses the supplements we take--vitamins as well as all the other products sold next to them in the grocery store aisles--glucosamine, melatonin, CoQ10, etc., plus a whole lot more that is usually only available at more specialized health and nutrition shops.

PDR for Herbal Medicines covers everything about plants used for herbal medicine--what exactly the herb is used for, what parts are used, the basics of how it's prepared, an exhaustive bibliography of modern research conducted, as well as unproven (not researched in modern times) uses.  It also has dosages, contraindications, and precautions to take.  Yes, it's a big book, and there's a lot in there that won't pertain to you.  But it has some really good information for those who really want to study.

The original Physicians' Desk Reference is updated each year.  The other three volumes are updated periodically.  All current editions are ridiculously expensive.  An older edition will serve quite well, and the money you save can be spent on supplies instead.

For further reading:
https://www.standardprocess.com/MediHerb-Document-Library/Catalog-Files/herb-drug-interaction-chart.pdf  (very handy 19-page chart of drug-herb interactions)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3191675/ (general overview)
https://www.ncbi.nlm.nih.gov/pubmed/17919554
https://www.ncbi.nlm.nih.gov/pubmed/27693910
https://www.karger.com/Article/Pdf/115345
https://www.sciencedirect.com/science/article/pii/S024886631401114X?via%3Dihub
https://www.ncbi.nlm.nih.gov/pubmed/17338474 (St John's wort and oral contraceptives) https://www.ncbi.nlm.nih.gov/pubmed/12397870 (St John's wort)
https://www.ncbi.nlm.nih.gov/pubmed/16005588 (St John's wort and kava)
https://www.ncbi.nlm.nih.gov/pubmed/29232282 (apple and fexofenadine)
https://www.ncbi.nlm.nih.gov/pubmed/12751275 (levofloxacin and orange juice)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5527439/ (diabetes medications and herbs)
https://www.ncbi.nlm.nih.gov/pubmed/946598/ (tetracycline interactions)
https://deserthopetreatment.com/drug-overdose/over-the-counter/ (dextromethorphan and St John's wort)
https://www.livestrong.com/article/423936-synthroid-interactions-with-vitamins/ (Synthroid interactions)

 28 may 2019