In the past year, reports that St. John’s Wort can interact adversely with a number of prescription medications attracted a lot of attention and alarm. These reported interactions need widespread notice, but not panic, among people who use herbal remedies.

As a physician with over two decades’ experience, and some 60-plus professional articles, in clinical drug research, I have acquired a perspective on drug interactions which many people, even doctors, may never arrive at on their own. The issue of drug-herb interactions is almost the same, with one important exception, which I will come to later.

Drug-drug interactions occur with virtually any drug you can name. By “drugs,” I include over-the-counter as well as prescription medications. There are so many drugs, and so many combinations of drugs, that no complete account of possible interactions exists or may ever exist, given the steady output of new drugs by pharmaceutical companies.

Anybody familiar with the statistics of combinations will realize how rapidly the number of possible combinations multiplies as the number of possible elements in those combinations increase. But think a little further: not only may any two drugs taken together yield effects that you wouldn’t expect from those of either drug alone, but the same point holds true even more when three drugs are used together, and likewise four, and …

I hope I’ve made my point: the number of possibly significant interactive combinations is astronomical, to the extent that no one can do controlled studies to test all of them for safety.

So, what kind of testing for dangerous interactions do pharmaceutical companies have to do to pass the strict criteria of our public guardians at the Food and Drug Administration?

Virtually none.

In fact, most drug study protocols specifically exclude use of other drugs while the subject/patient takes the drug under study. Often they also require some weeks of time (”wash-out”) from whatever the subject was taking before the study. Usually they allow, and may even record, use of everyday remedies like aspirin or Tylenol while patients are on the study. However, never do they actually look for interactions of even these common agents with the study drug. As for interactions with “vitamins” (often used in a vague way to refer to everything outside of the mainstream medical curriculum, including herbal remedies), even if subjects had the courage to report taking such “quack” remedies to a regular doctor, the researcher would probably not know what they were talking about, nor would the protocol have provision for identifying these “other” medicaments.

Well, you might ask, isn’t it unlikely that common, over-the-counter drugs will have any serious interactions with other drugs. Isn’t that why the FDA allows them to be sold without a prescription, because they are so safe?

I hope that those of you with young children know better. Aspirin overdose, especially when the aspirin is flavored to taste good, has killed many. But do you realize that Tylenol overdose has extraordinary liver toxicity, and Tylenol even without overdose can have similar catastrophic effects in combination with alcohol? Psychiatrists often have to deal with the aftermath of Tylenol overdoses, people who fail to kill themselves, but put themselves into such a grave medical condition that they face a much slower and more agonizing death in the hospital.

There are two exceptions to the usual failure to consider drug combinations in conventional research on new drugs. One is with drugs to be used for conditions in which they will almost invariably have to be used along with some other drug; for example, a drug used to treat diabetics must be examined for the possibility of an interaction with insulin. The other is when a combination is being studied for possibly greater therapeutic effect, such as the addition of lithium to an antidepressant for people with antidepressant-resistant depressions.

How then do we learn about drug-drug interactions? The same way we learn about extremely infrequent or delayed but dangerous side effects of a single drug, after the fact, when enough catastrophes happening to enough people to draw medical and governmental attention.

Does our medical ignorance about the myriad of drug-drug interactions sound terrifying? If it was that bad, doctors, who risk lawsuit over severe adverse drug effects, no doctor would dare prescribe a medication to anyone who is taking, was recently taking, or might in the future take, some other prescription or over-the-counter medication or even “vitamin.”

Tags: drug-drug interactions, herbal remedies, interact adversely, prescription medications

This entry was posted on Friday, December 25th, 2009 at 4:51 am and is filed under Prescription Drugs. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.