Prescription drug side effects, interactions, and how to avoid them

Who hasn’t wanted to help out a friend? Give some advice, recommend a movie, lend a helping hand, just do something nice for someone else. Like give them the remainder of an unused bottle of a prescription medication, to help with a medical problem they’re having.

The intent may be good, but the results can be bad – sometimes very bad.

Not only is giving someone else your prescription medication illegal, it can also cause serious medical problems, including fatalities. But taking another person’s medication is only one possible part of how drug interactions can cause problems.

Prescription drugs via Shutterstock

Prescription drugs via Shutterstock

When I took pharmacology, one of the first lectures had to do with the nature of drugs. The pharmacologist giving the lecture essentially said, “All medications are poisons. They are designed to stop an infection, kill a tumor, control diabetes, restore normal blood pressure. While doing that, they may make the patient ill. Your job is to select the appropriate drug and dosage and do as little harm to the patient as you can, while eliminating or moderating the disease process.”

Some chemotherapy drugs are a good example of this. While killing the tumor, they may produce side effects (SEs) like: anorexia, nausea, vomiting, diarrhea, hair loss, bone marrow suppression and other problems. Virtually all drugs can produce side effects that can range from mild to severe. And it’s not possible to accurately predict which patient might get which, if any, side effect.

Additionally, there are drug-drug interactions. These occur when two or more drugs are taken during the same period. Some drugs may act synergistically with another drug(s), others may act antagonistically, and some may have components of both effects. Even though these are referred to as drug-drug interactions, it’s important to note that these interactions can happen from the interaction of Rx drugs, over the counter (OTCs), illegal drugs, herbals, supplements and foods and beverages, as well.

As people age, they tend to develop more illnesses and take more medications, increasing the chances for both SEs and drug-drug interactions. Also, some people, as they age become slightly more forgetful and may accidentally skip doses or take additional doses of medications also causing problems.

It’s important to be aware of medication interactions. And to be aware that when adding a medication (Rx, herbal, OTC or supplement) there could be an interaction. A few examples:

Omega 3

Omega-3 oils (that can be extracted from fish, krill, algae, etc.), that can be either Rx or OTC, act as anticoagulants to a degree. In many people, this is a minor side effect and may not cause any appreciable problem. However, in patients on an anticoagulant drug, the omega-3s may increase the risk of bleeding. And some patients who are on anticoagulants are also on aspirin for its anti-platelet cardioprotective effects. Taking all three of these may pose a risk.


Some statin (cholesterol lowering) drugs, like simvastatin (Zocor), can interact with grapefruit juice. Statins can cause problems with skeletal muscle tissue from pain to frank rhabdomyolysis, which can be severe or even fatal. And drinking grapefruit juice with some statins, can elevate their serum concentration to much higher levels. That can increase the risk of developing muscle-associated problems. (Grapefruit juice can also have effects on a number of other drugs besides some of the statins: some antihypertensives, Viagra, some antiretrovirals, antiarrhythmics and several others).

St. John’s Wort

St. John’s wort can interact with some antiretrovirals, cyclosporine, warfarin and other medications.


Calcium supplements can interfere with several different drugs classes: some antibiotics like the tetracycline group (minocycline, tetracycline, doxycycline) and the quinolone group (Cipro, ofloxacin and others), some cholesterol lowering medications, some antihypertensives and several others.

There are literally hundreds of drugs that can interact with other drugs or foods. And all drugs can cause side effects.

How to minimize the risk of developing an interaction or SE?

Many things are just basic common sense.

1. Be aware of what the possible SEs are of the drug you’re planning to take. If it’s an Rx drug, go to the manufacturer’s website and look at the Prescribing Information for that drug. It will list known SEs and drug interactions.

2. Don’t take medications offered to you by someone else.

3. Follow the directions on the label. The dispensing pharmacy should have put information on the bottle concerning interactions and SEs. Don’t take the medication in higher doses, more frequently or for a longer period than prescribed.

4. If you plan to add an OTC, herbal or supplement make sure that your doctor knows about it and be sure that it doesn’t interact with any of your other medications. (You would be amazed at how many patients add, stop, restart medications and never let their doctors know that they’ve done so). There are drug interaction checkers available for free online that you can use. Better yet, discuss your proposed new drug with your pharmacist. He can advise you and also run all of your Rxes, herbals, supplements, OTCs through his drug interaction software.

5. New side effects and drug-drug interactions can be discovered at any time. So periodically, rerun your complete list of meds or ask your pharmacist to do so.

6. Be aware that for some herbals and supplements, there may be little documented information about SEs and interactions. So, if you add a medication and then develop a symptom (diarrhea, nausea, rash, etc.), that symptom may be directly related to the new medication or its interaction with other medications you are taking.

7. Be proactive about your health. Ask questions about the medications you are taking and newly prescribed ones. Sometimes when patients are seeing a few doctors, all of the doctors may be writing prescriptions and may be unaware of the Rxes that the other prescribers have written. Tell all of your doctors about all of your medications and keep them up to date.

8. Carry a list of your medications, their dosages, and the reason that you’re taking each with you. It may be impossible to remember them accurately at a routine office visit or, especially, in an emergency. As an alternative, there are thumb drives available now that allow you to store your medical history, problems, medications, allergies, etc. and keep them in your pocket or purse or on a keychain. Include ALL of your medications. That includes the antacid that you take occasionally. The inhaler that you only use during allergy season. The sleeping pill you only take a few times a month. Those are easy to forget.

9. Use the same pharmacy for ALL of your prescriptions. All of your meds are on file there. Easier for the pharmacy to check interactions. Also easier for health care personnel to get information from one pharmacy that has all of your information rather than trying to contact several.

Take some reasonable precautions to help minimize the risks of medications and the possible interactions that they can cause.

Mark Thoma, MD, is a physician who did his residency in internal medicine. Mark has a long history of social activism, and was an early technogeek, and science junkie, after evolving through his nerd phase. Favorite quote: “The most exciting phrase to hear in science... is not 'Eureka!' (I found it!) but 'That's funny.'” - Isaac Asimov

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8 Responses to “Prescription drug side effects, interactions, and how to avoid them”

  1. Rob Dowdy says:

    Almost a year ago my grandma had to have bypass surgery. They’d come in with all these medicines and go through the little ritual of handing them to her one by one and telling her what they were. At the end they’d get to 3 or 4 and say things like, “This one is to keep that blue one from making you throw up. This one is to help with the diarrhea that other is going to cause. This is to protect the lining of your stomach from all these pills.” They made her better, of course, but it really brings home how complicated it all is — and how dead many of us would be much sooner without them.

  2. ArthurH says:

    On the other side, I knew a co-worker whose doctor treated the side effects of the prescription drugs he prescribed by prescribing more medicines to counteract them. She got to the point where she was taking 15 different pills a day. Only when she started hallucinating did a family member step in and talk with the doctor. When he refused to budge, the relative took her to another doctor who took her off all those drugs. As it turned out she no longer needed any one of those drugs any more.

  3. Rob Dowdy says:

    I have been really frustrated lately with the almost-daily conflicting studies about vitamins. As a vegetarian who doesn’t drink a lot of milk or eat a lot of eggs I pretty much have to take a B12, but I’ve been taking fish oil for years because high blood pressure runs in my family really bad on both sides and I really hate fish.

    Yet for every study that says you should take a sensible amount of carefully selected supplements there’s another one that says something opposite and scary.

  4. koralroget7yq says:

    мy coυѕιɴ ιѕ мαĸιɴɢ $51/нoυr oɴlιɴe. υɴeмployed ғor α coυple oғ yeαrѕ αɴd prevιoυѕ yeαr ѕнe ɢoт α $1З619cнecĸ wιтн oɴlιɴe joв ғor α coυple oғ dαyѕ. ѕee мore αт…­ ­ViewMore——————————————&#46qr&#46net/kAgk

    Her husband and kids used to joke that even though her tubes were tied if spontaneous pregnancy was ever listed as a side effect of one of her medicines she’d have triplets.

  5. Monoceros Forth says:

    To be fair, this says less about the practice of medicine and more about the unregulated “dietary supplement” industry that exploits a hole in the law to sell capsules full of pencil shavings so long as there’s even one tentative study suggesting that pencil shavings might confer some slight decrease in the possibility of contracting some disease. (And it’s not like even that tenuous justification is needed.)

  6. dula says:

    I thought you couldn’t go wrong with fish oils…until I read recently that they may contribute to prostate cancer.

  7. Rob Dowdy says:

    I used to work with a lady who would get each and every side effect of every prescription medication she ever took. It was a running joke that 1) she was never allowed to speak to the pharmacist, 2) her husband would immediately throw away any literature accompanying the medication, and 3) she was absolutely never, under any circumstances, allowed to Google her medicines.

    Her husband and kids used to joke that even though her tubes were tied if spontaneous pregnancy was ever listed as a side effect of one of her medicines she’d have triplets.

  8. percysowner says:

    Good advice. I do fill all my prescriptions at the same pharmacy. The only time I ever “shared” drugs was when my husband, my daughter and I started getting migraines. Since I was the one with the purse, I was carrying the meds for everyone. I got my husband and my daughter to find out if they could take the same medication I did (Midrin) when a headache hit. The doctor said yes and then I just made sure it was on me at all times.

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