We Should Be More Scared of Herbal Teas

Sam Westreich, PhD

“It’s not dangerous, it’s all-natural! Delicious, natural nightshade!”

Is her drink healthy? Or is it toxic? Will it help pregnancy, or put an unborn child at risk?Photo byPhoto by Candice Picard on UnsplashonUnsplash

There’s always a tendency to assume that natural things are better. Food? Better to be natural, no weird genetics or chemicals applied. Furniture? All wood, all natural. Clothes? Don’t give me synthetics with microplastics, we should all be wearing natural fibers.

I’m not saying that this approach is totally wrong. When it comes to food, for example, preservatives are both artificial and can be damaging to our gut microbiome. And there’s real concern about clothing-based microplastics leaching into our bodies or the environment.

But this embrace of “natural is better” can sometimes lead to us underestimating the dangers of natural products. We assume that something natural is going to be healthy and won’t hurt us, simply because it came directly from nature.

You know, like arsenic and nightshade.

One place where this comes up a fair bit is with teas. “Herbal teas” are generally assumed to be both beneficial and harmless to us, but the truth is a lot more concerning.

After all, a lot of the “nasty, artificial” drugs that we’re prescribed came originally from herbs.

Licorice root, mugwort, and passion flower…

There are lots of teas out there that contain all sorts of natural-sounding ingredients, with names of vaguely familiar plants. Take this one, for example:

Womb warming tea - but is that a bad thing?Photo byWisdom of the Womb

It’s supposed to help “improve uterine health to encourage a more nurturing womb environment.”

It contains:

Mugwort, Raspberry Leaf, Red Clover Flower, Alfalfa, Skullcap, Orange Peel, Honey, Cinnamon, Fennel, Licorice, Dang Gui, Black Cohosh, Galangal, Ginger, Go Ji Berries

All organic, of course.

But these ingredients aren’t really great for the tea’s stated goal. Take mugwort, the first listed ingredient. According to the NIH, mugwort is a plant to be avoided during pregnancy, because it can cause uterine contractions and start menstruation, aborting a potential pregnancy.

Licorice is also mentioned on here — but licorice root, when consumed in large quantities during pregnancy, has been associated with premature birth and health problems in children.

Other compounds in here, like black cohosh, haven’t been definitively linked to pregnancy issues, but are sometimes recommended out of a belief that it can start labor. Black cohosh is mainly recommended for menopause, not pregnancy.

And there’s another huge problem, which is dosage.

Enough energy drinks will shut this whole thing down

“The dose makes the poison.”

— paraphrased from Paracelsus, 1538

Some compounds, like aspirin (natural! From willow bark!) can heal you. Others, like cyanide (natural! From apple seeds!) can kill you. But for almost every compound or chemical that we put into our body — yes, even the natural ones — the dosage is what determines whether it helps or harms us.

Consider caffeine. Too much caffeine is fatal — yes, literally. There are online calculators that will estimate how many energy drinks it will take to bring you down; for me, downing 62 cans of Monster will be a likely fatal dose.

Dosage is especially important when it comes to medical drugs. Consider warfarin, a drug that prevents blood from clotting. For someone who has had a heart attack, has an irregular heartbeat, or has an artificial heart valve, it’s lifesaving.

But take too much and it becomes deadly. In fact, warfarin has such a low efficacy window that doctors often start patients on a too-low dose and slowly increase it until they start seeing benefits, rather than risking an accidental overdose. A number of genome-wide association studies have focused on looking for the genetic variants that determine whether a person is more or less sensitive to warfarin.

Put it all together, and it’s vital to know the dose of a compound you put into your body.

But herbal teas don’t offer that. In fact, the dosage received from a cup of herbal tea will likely vary from bag to bag, as well as based on how strongly you steep it.

This means that, even if you consume a consistent amount of tea per day (say, three cups), the actual dosage of compounds from the herbs is likely to vary significantly. That’s bad, from both a health and a harm standpoint:

  • If one of those herbs has a helpful effect, you won’t get it consistently unless you take a ton of tea to make up for low-dosage days.
  • If one of those herbs has a harmful effect, you may be inconsistently poisoning yourself.

And we haven’t even touched on interactions yet!

Herbs are drugs, and they can have bad combinations with other medications

That’s right. Guess what happens when you mix one molecular compound with another one inside your body?

Sometimes, nothing. Sometimes, one drug will make the other more potent (stronger). Sometimes, one drug will make the other less potent (weaker).

And the herbs that are in various teas can contain compounds which act like drugs, and will interfere with other meds, sometimes with disastrous results.

For example, that black cohosh that we mentioned earlier? That can react with common medications like Lipitor, alcohol, and Tylenol, causing liver toxicity. Strangely, nowhere on that tea’s website does it mention that the tea shouldn’t be consumed along with alcohol.

Other herbs can be dangerous as well. Evening primrose oil is sometimes used to help treat nerve pain from arthritis or diabetes, but it also slows blood clotting — which means that, if consumed by someone who regularly takes prescription blood thinners (remember warfarin, from earlier?), it can lead to heavy bleeding, either internally or externally, that won’t stop.

One other commonly consumed herb (that probably shouldn’t be as widely offered as it is) is St. John’s Wort. It’s often recommended for depression, but it happens to interact with a lot of other medications, including anti-depressants like SSRIs and MAO inhibitors, and birth control.

Weirdly enough, the top listing for St. John’s Wort tea on Amazon does not mention any risks of drug interactions.

Herbal teas contain varied levels of real drugs that can have real (dangerous) effects

Add it all up, and herbal teas may be worth treating with a bit more caution and respect. Even though all of these teas are made from nothing but natural plants, those plants also produce a lot of molecules that cause effects on our body, like prescription drugs.

Many times, the herbs are chosen for a tea because they’re “associated” with a condition, like grabbing any herbs linked with pregnancy and putting them in a “fertility tea”. But those herbs may not have the intended results, and could cause far more damage.

Additionally, with herbal teas, you cannot ever be certain that you’re consuming a safe dosage, or even a consistent dosage from one cup to the next. And are you going to take the time to Google every ingredient in your herbal blend to see whether it interacts with any drugs you may be taking?

If you don’t want to put in that level of effort, it’s probably best to skip the herbal teas.


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A microbiome scientist working at a tech startup in Silicon Valley, Sam Westreich provides insights into science and technology, exploring the strangest areas of biology, science, and biotechnology.

Mountain View, CA

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