Critical Thinking for Contraindications

Contraindications are situations where an herb is not indicated, either because of a potential interaction or a potential bad outcome. Contraindications can seem scary or overwhelming for the home herbalist, since the stakes are high and the rules unclear, especially with complex medical conditions, children, and pregnant people. This article presents tools for thinking critically about contraindications, to allow the home herbalist to contextualize and understand them.

It is helpful to think of contraindications as an additional set of details to help you determine if you’ve chosen the right herbs: Cayenne may be great for arthritis, but if the person in question has an ulcer, Turmeric might be a better bet. Both are anti-inflammatories specific for muscles and joints, but Cayenne can be very irritating to wounds and can even increase bleeding by breaking up clots. In this situation, the extra detail of the contraindication gives clarity that Turmeric is the better choice. [See Heart & Hearth #2 in Plant Healer Magazine for more thoughts on choosing herbs in an organized fashion].

Consider contraindications an open door, an invitation to explore deeper into herblore.

Note: For our purposes, I’m using a broad definition to include drug interactions as well as people with physical conditions who may experience adverse effects. Many references will separate contraindications and drug interactions, but for our discussion here the same principles apply to both.


Fear versus Respect
Do not fear herbs. No one ever made their best choices when motivated by fear. A complex situation offers the opportunity to enrich your knowledge:

jump at the chance to become even more of a badass fairy herbmother.

Use new herbs with respectful caution, especially with complex physical conditions or pharmaceuticals at play. Traditionally applied herbs are overwhelmingly safe (with some notable exceptions, please back slowly away from the foxglove). Potentiation and agonist/antagonist activity are where most danger lies, and doing a little research can clarify that. Unexpected physical consequences—like valerian’s paradoxical hyper-awake anxiety state, or hops’ rebound high blood pressure—can usually be avoided by intentionally, carefully following traditional uses and methods of preparation.

When to Look Deeper
Most of the time, it’s sufficient for the home herbalist to know that an herb is contraindicated, without having to do a deep dive into the whys and hows of it.

There are three main situations where we need to investigate contraindications in depth:

  • If normal herb usage is complicated by unrelated medications or conditions, like helping someone who takes blood pressure meds with their menopausal insomnia;
  • Times when we use herbs for complex medical conditions or as adjuncts to medications, like helping a relative with their anxiety while they go through chemo, or working with someone with rheumatoid arthritis who also uses methotrexate;
  • During pregnancy, as the ever-fear-mongering Dr. Google will yield a warning for almost any herb in pregnancy if you look hard enough.

In these situations, we explore the contraindication in order to discern if it truly affects this situation, and if so, how much.

Always Questioning, Always Learning: Critical Thinking

It’s important to understand that some contraindications are essential to follow and others are simply moments to pause and consider carefully, a trigger for extra caution.

Some contraindications are known: Cotton Root is contraindicated in pregnancy because it could cause an unwanted miscarriage. Licorice is used with caution when high blood pressure, heart, liver or kidney disease is an issue because of fluid retention and electrolyte imbalance (pseudoaldosteronism). Others are suspected: an herb that depresses the central nervous system could potentially cause problems if it was taken with a pharmaceutical that did the same thing, so check first. Others are purely hypothetical: an herb may be contraindicated in pregnancy because rats walked strangely after having massive amounts injected into their backs.

With those opposing options, how do we effectively navigate the labyrinth of warnings to determine whether or not an herb is appropriate? How do you know which rules to bend and which to honor?

We use our beautiful brains’ critical thinking magic to separate the wheat from the chaff.

Understanding the origin of a contraindication is an essential step in the critical thinking process. The essential question is WHY is this herb contraindicated? Is there tradition, evidence, or what? An unfortunate number of herbal books refer to the same few contraindication references without further explanation, which makes it extremely challenging in the home setting to suss out whether something is truly a problem, or just a moment for caution; it’s even worse when the books contradict each other—which they often do!

Once we understand why something is contraindicated, we can look deeper to make appropriately judicious choices. For example, Ginger is listed in many books as contraindicated in pregnancy, because rats fed mega-doses had miscarriages, despite numerous convincing human studies of its safety and its traditional use in pregnancy. Once you understand the origin, you can make an informed choice about safe use.

The goal of this article isn’t to present an encyclopedic list of contraindications and drug interactions, but to provide a framework to think about them and make informed decisions. We are not walking encyclopedias of all things herbal at all times. “Let me look that up and get right back to you” is the mark of a good herbalist, not a bad one! The safest course is to learn new herbs thoroughly, and research drugs and conditions when you need to.

Critical Thinking Framework for Contraindications

Ask yourself: does this person have a condition or medication that might affect your choice of herbs? If so, ask the following questions. If you find a contraindication, ask why it exists.

1. For medications:

What is the mechanism of action?

Will your herbs interfere or potentiate it?

What will happen if they do?

What is the metabolism pathway?

Will your herbs interfere or potentiate it?

What will happen if they do?

What are the warnings the drug database provides and do they give you any clues of things to worry about? (For instance, orthostatic hypotension will be an issue with herbs as well as drugs.)

2. For conditions:

How does the condition work in the body?
Identify potential issues: liver, bleeding, over-sedation etc.

3. You are now well informed! Pick your herbs, then use your research to think critically to decide if they’re the right fit:

Any actions or indications that might reveal a potential issue?
What do we know about how the herb works in the body?
What’s the suspected mechanism of action, and could that affect things?
Has the herb traditionally been used for this? If not, what do other people use?
Is this herb the gentlest and most appropriate (energetics, indications)?

4. Risk/benefit Analysis:

What will happen if you’re wrong?
How likely is it that there will be a bad outcome?
How likely is it that this herb will help this person?
Do the potential risks outweigh the potential benefits, or vice versa?

Get comfortable with the idea that when things are hard, we must work harder, and as a reward we greatly expand our knowledge. It is appropriate to do extra research for complicated situations, and every foray adds to your adventure in the nerddom of herbalism.

Types of Interactions

Sometimes we use “contraindications” as a blanket term to also include herb-drug and herb-herb interactions; other times we break those out into their own category of “interactions.” Either way, it’s important to understand how interactions affect herb choice. There are several types of interactions, including

Synergy: “The whole is greater than the sum of its parts” is the classic phrase used to describe synergy. Simply put, synergy is the principle that something wonderful happens when things are combined, within the plant itself, within the formula, within the forest biome, at the party… [See Heart & Hearth #1 in Plant Healer Magazine for a further discussion of synergy.] As synergy relates to interactions, though: some herbs make new things happen when they’re combined with herbs or drugs. Black Pepper and Ginger increase the body’s absorption of other herbs. Licorice magnifies the action of many herbs, and seems to decrease toxicity of many herbs in formulation.

Many herbs are potentiators: they make others work more strongly. This is great if it’s on purpose; I like to add a few drops of Artemisia to a panic attack formula, not enough to effect the balance but enough to help the other herbs find their way in. But potentiators can be problematic at times, if the response is over-magnified to a dangerous degree.

Agonists bind to receptor sites and make stuff happen that is similar to the thing that’s supposed to bind there. Antagonists block the action of other things by binding to receptors without generating a response. This concept gets complex, with partial agonists, mixed agonist/antagonists, and various other combinations; for our purposes, it’s enough to know that it’s a thing. Think of locks: some keys don’t fit, some keys fit but won’t turn, and other keys fit, turn, and open the door.

This can be extremely useful: Lobelia is an agonist-antagonist for nicotinic receptors in the brain, so it can help a person quit smoking by binding to the receptors and eliciting a similar but lesser feeling than nicotine, and then when you fall off the wagon and smoke anyway it doesn’t feel good because your beautiful friend Lobelia is guarding those receptors for you.

Red Clover binds to estrogen (estradiol) receptors and elicits a lesser effect similar to estrogen, providing a measure of relief in menopause and blocking harmful, carcinogenic xenoestrogens (plastic, pollution, pesticides) from binding to estrogen receptors (thank you, dear friend).

St John’s Wort is an antagonist at a bunch of neurotransmitter receptors, blocking the reabsorption of happy-making chemicals so the happy lasts longer. Yay.

Metabolic Pathways: When we improve the body’s filtration systems (liver, kidney, lymph), many drugs have interactions. This is because your beautiful body correctly identifies drugs as not part of you and therefore something to be excreted, fabulous genius thing, and is more efficient at removing said toxins because of the herbal boost you gave it.

For example, SSRI medications (a type of antidepressant) must stay in the body at an effective level for a specific period of time until the next dose. Giving Milk Thistle with prozac or zoloft can be counterintuitively problematic, since improving liver function speeds up the clearance of drugs, improving liver health but decreasing the medication’s effectiveness.

This isn’t life-threatening (unless the medication sustains life) but it can be problematic for someone who relies on a consistent medication level, so close attention must be paid when combining herbs that stimulate the liver and kidneys with medications.

And, remember, we don’t actually know how herbs work most of the time, because life is a complex mystery. Science is both miraculous and largely uninterested in our corner of the nerd phylum; so it is ABSOLUTELY reasonable to assume there could be unforeseen herb-drug interactions in the crowded hallways of your nephrons.

Searching for Answers

When you need guidance on contraindications, go first to written resources. Books, especially contraindication/interaction references but also PDR’s and herbals, are an essential resource. Online drug databases are extremely useful as well; stick with the ones written for professionals, because the ones written for consumers won’t tell you what you need to know.

Once you’ve exhausted the written research route, ask your mentors and peers. Remember that we practice a tradition that is thousands of years old: there’s Yarrow in a 65,000 year old cave in Iraq, you are not an island inventing herbalism, so peers and mentors are an essential resource. It’s important to do the research first for several reasons: first, there may be a pretty obvious answer when you look into it, and you’re not wasting your “I have a question” tokens on something you can figure out yourself; second, you will learn it more deeply if you research it; and third, if you can’t find the answer, you have a stronger foundation to ask a more intelligent question.

Referrals are also a resource: when in doubt, pursue a conversation with another provider, perhaps the person who is managing the condition or medication in question, and consider sending the person to see someone who is more familiar with their situation.

Strength of the Evidence
There is a lack of scientific evidence about contraindications and interactions. There is limited funding for herbal research, and the studies we do have are often problematic. Many studies don’t effectively test the herbs: either insanely high concentrations of isolated phytochemicals (a year’s worth per day, etc.), or they use the wrong species or part of the plant, or they don’t standardize the preparation, or they lose 2/3 of the subjects and don’t say why…we use what research we can, but the problems are myriad. Anecdotal ancestral traditions are often the best evidence available to us, and honestly, I’m comfortable following thousands of years of healing tradition…combined with critical thinking and a deeply rooted understanding of the herbs.

Issues with the References
Many references report speculated contraindications (as in, it is reasonable to assume it’s a bad idea, like abortifacients in pregnancy), without clearly relaying that it’s just an educated guess. This is problematic because they’re not differentiated from well-researched and traditional contraindications, so it’s impossible to tell which ones are carved in stone and which just mean “be careful.” This is an even bigger problem with internet sources, which often quote scientific language that originates from misleading or inaccurate articles.

Honestly, it’s crazy-making. The only way around it is straight through: look it up in a couple of different places, with the goal of figuring out why it’s listed as contraindicated.

I’ve found these references helpful, because they explain why things are contraindicated and go in depth about the available research. Unfortunately, the reference books are all pretty outdated and science moves quickly so it’s important to take a peek online too, but very cautiously. There is a ton of terrible information online, so specific searches like “garlic interaction digitalis 2015 2016 2017” helps narrow the field. It’s too bad there isn’t a reliable free contraindications database, but until someone makes one, these books are extremely useful:

The Essential Guide to Herbal Safety by Mills & Bone: this is my favorite—they get a little sassy sometimes in their dry scientist way, it has great charts, and it’s the least conservative reference I’ve found. It’s intimidatingly huge but worth it. I wish we could get a new edition released!

Herbal Contraindications & Drug Interactions plus Herbal Adjuncts by Brinker: this is probably the most famous one, it’s useful if you want to look at a specific herb but it’s not well indexed so it can take forever. It’s more conservative than Mills & Bone but still helpful.

Botanical Safety Handbook from the American Herbal Products Association: this is a huge reference that has a ton of information about a zillion herbs. It’s the most comprehensive, but also very conservative in its recommendations. Definitely extremely useful in conjunction with other resources.

Commission E Monographs: This is a series of in-depth monographs on medicinals from the German version of the FDA. They’re super old (1990s) but still useful, and extremely conservative since it’s from a government. You can read them on the American Botanical Council’s website (where you can also get a copy of The ABC Clinical Guide to Herbs, a similarly old book of useful monographs).

I also usually look at traditional uses when I’m checking out contraindications for conditions.

Native American Ethnobotany by Moerman: I use this one all the time, especially since I work primarily with bioregional herbs (and now there’s a searchable database!)

Modern Herbal by Maude Grieve: comparatively recent (1930’s), super big and useful for traditional uses

The many Eclectic texts are fascinating, but they take a level of skill to explore since the language is archaic and the science is different. Best to have a strong foundation of herbal knowledge going in. They can be read on the fantastic websites of Michael Moore and Henriette Kress.

Contraindications as an Opportunity for Allyship

Beware of Dog(ma)

Often when a question arises about drug interactions, someone eventually chimes in with the suggestion to stop the medication in question. The myth that natural medicines are best for all people always is a trap to avoid. This is an ableist white supremacist cisnormative worldview that “others” everyone who has been included in the multifactorial socioeconomic factors that influence health determinants. Don’t presume that your life experience and advantages are universalizable; they’re not. There are many reasons why someone might be best served by pharmaceuticals, surgery, etc. Your goal as an herbalist is not to get someone off their meds, unless that is their goal, but to help provide the tools they need to accomplish their goals through their own agency. Herbs can be helpful as adjuncts to conventional treatments, or for a different issue entirely.

Honor the Past
Another aspect of our work promoting self-empowerment is acknowledging and validating our clients’ fears of their health status and necessary herbs/medications/procedures, and then to STRIVE ACTIVELY to make sure those fears aren’t realized. Helping others navigate their health status from a place of power is important, and it relates to this topic in that we are given the opportunity to touch on both fears and contraindications when serious health conditions, procedures, or medications are present. From a trauma-prevention model, these fears could be said to stem from a deeply rooted disempowerment around our bodies and health choices, especially in communities that are actively disempowered by the existing power paradigm. Our fears are justified and have been realized over and over throughout our lives, in recent memory, and in ancestral memory. As healers, it is incumbent upon us to not pretend the fear isn’t a valid self-protective mechanism, but to embrace the ways we have all learned to survive, and strive to help folks self-empower to confront them.

[If this is news to you, google “Tuskegee syphilis experiment” and picture your family narrative if that was your mother’s brother; or, next time you fill out a form in a medical office, consider what your responses might be if you were not cis-gendered. See Here for additional discussion of the principle of self-empowerment in herbalism].

A Word About Polypharmacy

For people with complex medical conditions, a helpful act of allyship is to examine polypharmacy. Polypharmacy refers to taking many medications at once, and the problems that can arise from drug-drug interactions, dosage errors, and over-medication. We can help clarify why they’re taking each drug, ensure the dose is correct, and that there are no interactions causing more problems. Sometimes, worsening conditions are actually drug interactions, especially with elders because many conditions affect them differently. For instance, confusion is a clinical sign of a urinary tract infection that is often mistaken for dementia. Have the person request a polypharmacy evaluation from the nurse at the primary prescriber’s office, and offer to help interpret. If one dose is adjusted, one drug is found to be a duplicate, or an alternative medication is found that doesn’t require treating side effects, then our clients are healthier, happier, active agents of change in their health (and suddenly it gets a lot less complicated to provide herbal adjuncts). Do not fall prey to tunnel-vision: interdisciplinary collaboration with prescribers is essential in promoting self-empowerment and autonomy.

Final Thoughts

Contraindications are an essential part of Materia Medica, but unfortunately, they are also overly abundant and poorly defined in most references. Many often-repeated warnings are the result of bad science or even sensationalized guesswork by people outside of herbalism (Tonight at 10: Tea that Kills in Your Grocery Store!). Home herbalists greatly expand their skills by using critical thinking to examine questionable warnings and deepen the herb selection process. Which contraindications are rules, and which simply inspire moments of caution? Herbal practice gains great depth when we learn which potentiation interactions can be used as an herbal adjunct to improve health. Taking the opportunity to investigate deeply presents opportunities to nurture your growing herbal skillset.

Don’t get put off by the fancy language on contraindications and drug interactions. You know to shake salad dressing because oil and water don’t mix. You’ve got this too.


This article was originally published in Heart & Hearth, my Plant Healer Magazine column on Radical Family Herbalism.  Link in the sidebar to subscribe to the magazine and support my work!

One thought on “Critical Thinking for Contraindications

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s