It is inevitable when teaching that someone asks if an essential oil (EO) can “cancel out” another essential oil when creating a blend. This could be from an olfactory sense as well as a chemical component sense. The answer is multivalent just as an essential oil and the practice of aromatherapy is. My fun and frustrating answer is that we don’t really know as each person and case is different but when you step back and consider a few concepts the answer is “probably not” (note: see the “sidebar” at the end of this article for consideration points on research). This is dicey territory. Several factors should be weighed before jumping to conclusions including the route of administration (i.e., olfaction, respiratory support, dermal penetration or internal), plants used (i.e., essential oils), the person’s constitution and symptoms among other facets. There is a “problem” when a practice such as aromatherapy is examined through a myopic lens (i.e., only “active components,” chemistry, pharmacology) versus a kaleidoscope (i.e., holism, complete essential oils). Though said myopic views creep into practice, out of necessity, due to the reality of pharmodynamic interactions (i.e., contraindications, medications taken and how they are metabolized).
Three terms that often come up regarding essential oil components interacting with medication AND blending are synergism, additivity and antagonism. Something to keep in mind when framing these mostly pharmacological terms around aromatherapy is that the context is often different; the pharmacological perspective favors single chemicals (i.e., targeted drugs) which are “easier” to analyze whereas aromatherapists work with genuine and authentic essential oils which are comprised of an array of chemical components and administered via several possible routes. Let’s approach the definitions from both pharmacology and holistic aromatherapy perspectives:
|Effect of 2 (or more) combined chemicals is > each chemical individually||Effect of 2 (or more) chemicals is = the sum of the 2 chemicals taken separately||Effect of 2 (or more) combined chemicals is < each chemical taken individually (i.e., inhibition, interruption)|
|1+1 = 3||1+1 = 2||It’s not quite 1+1 = 1.5 as these either compete with the same receptors or are metabolized in the same pathway.|
You’ll note above how there are negatives (-) and positives (+) to the three categories; this ties back to a core tenet of any practice: intention. What is the core issue at hand, what are the symptoms, what is the person’s constitution and how may the plants and delivery of their medicine align with that person acknowledging there may be upsides and downsides?
I believe aromatherapists work with all three concepts when blending from a synergistic approach and that the synergistic approach is inherent in blending essential oils.
Of course we ask what, if any, medications our client may be taking and we cross-reference safety data. But we also keep in mind how there is a large palate of EOs to work with and may acknowledge that EOs as a group, unlike pharmaceuticals, are not known to inhibit bodily processes. Conversely, essences generally enhance or potentiate both body and mind, supporting a whole person in their innate ability to heal. Essences promote shifts and initiate change.4
I propose we continue appreciating and respecting the pharmacological approach of relating to essential oils when appropriate, yet consider repositioning the way aromatherapists reference pharmacodynamic and pharmacokinetic interactions by framing them differently, as context described earlier (i.e., dilution, route of administration, health of the individual, etc.) must be taken into consideration.
Let’s consider these three interesting words as they may relate to working with essential oils instead of targeted drugs.
Synergy: Enhancing and Potentiating by Working Together
Synergy is about magical parings. It is akin to an orchestra where each person and their instrument is seamlessly working with the group to effortlessly perform the perfect concerto. It’s when 3 to 5 chosen essential oils meld into each other becoming more dynamic than could be imagined. Keep in mind that essential oils are terpenes by definition. Although they share many terpenic components there are several plants which have unique terpene or phenylpropenoid components which make things a bit more complex and interesting.
When working with a single essence or a blend of 3 to 5 oils there is always inherent synergy within any particular essential oil. There is a reason a plant produces what it does. A major biosynthetic purpose of a plant essence is to communicate with and respond to the environment. This is interesting when an “active component” is shown to do harm when isolated,5 though not when viewed holistically as the antidote is often found in the plant6.
Synergy may also be conceptualized as “potentiating”7. An example is a hot, itchy, dry skin condition (e.g., eczema) that presents or flares up due to stress (note: a holistic approach seeks the underlying cause and considers factors like lifestyle and nutrition). Let’s say I choose a monoterpene-rich oil like Boswellia sp. for both enhancing dermal penetration and its cooling/soothing qualities on the skin and expansiveness for the mind; I enhance that with Commiphora molmol for more cooling and deeper reparative work (and stilling the mind). To round out the blend I add Pogostemon cablin, Rosa damascena and possibly Vetiveria zizanoides for further calming of the mind, supporting “rest and digest” response, cooling (also more wet than drying) and overall affinity for the skin health. All of this would go in a base of aloe jelly mixed with rose hydrosol. Many of the aforementioned oils have different compositions yet they are known to work well together for skin conditions. To top it off, they smell amazing together.
On the subject of smelling better together: that’s part of the synergy. If a person loves the way their aromatic product smells, they are going to love using the product! More on that later…
Additivity (Sometimes, but Not Always, Called Agonism)
From an aromatherapy perspective, consider this as “stacking” molecules in order to increase the efficacy (I dare not write “potency”….) of a blend. From a pharmacology standpoint, “additivity” most often means drugs having similar mechanisms of activity are magnified and the effect causes harm (e.g.., SSRI drugs (Prozac) paired with Triptans (for headaches) cause serotonin syndrome; NSAIDS with Glucocorticoids increase the risk for abdominal bleeding). EOs are complex molecules and it doesn’t do them justice comparing them (apples) to targeted synthetics (oranges). Instead, turn to essential oil chemistry for guidance in identifying therapeutic actions, red flags and therefore usage indications and routes of administration. For example…
- Let’s say I have a dry, spastic cough and turn to Salvia sclarea, Pinus sylvestris and Boswellia papyrifera or ssp. as a blend I feel suits my needs (i.e., gentle, soothing, balsamic, anti-spasmodic) combined with a steam inhalation. This synergy has oils high in esters supported by monoterpenols and of course monoterpenes.
- What if an otherwise healthy adult presents with stuck mucus that would benefit from mucolytic and expectorating EOs? I may combine the following oils in a synergy to then add a couple of drops to a steam inhalation: Rosmarinus officinalis (all chemotypes considered), Eucalyptus ssp. and Mentha x piperita. These are oils high in ketones supported by 1,8 cineole & monoterpenols.
So what is this? It’s something I think of as “stacking,” where I may:
- (A) Choose 3 to 5 oils that are well represented by 1 or 2 dominating components (e.g., 1,8 cineole + 1,8 cineole) and/or
- (B) Choose “family rich” oils known for their general actions (choosing oils rich in esters in general).
The underlying concept of antagonism is when a molecule blocks an action of another molecule from initiating an action for a “known” outcome (in aromatherapy this often refers to using an aromatogram with various strains of bacteria put against single oils or blends of those oils to determine efficacy). I believe antagonism is where we may consider contraindications which have been culled over the years from the healing arts.
When you understand plants and certain chemical components it becomes apparent that contraindications are generally exceptions to the notion that steam distilled EOs (terpenes) are safe when used in acceptable amounts. This is where it’s important to know the more “potent” components and EOs that are contraindicated for specific conditions. Following are a few examples: methyl salicylate is contraindicated for those on “blood thinning” medication and trans-anethole for those with excess estrogen-dependent health issues; Juniperus communis is contraindicated (internally) for those with kidney issues, intense use of Rosmarinus officinalis is contraindicated for high blood pressure whereas Canaga odorata is contraindicated for low blood pressure.
In the realm of antagonism I propose we look at the concept of “quenching” versus an EO “blocking an action/outcome” as most essential oils in a person’s toolkit are not exceptions to the GRAS notion and we understand that EOs do not stop bodily processes. Quenching comes in handy when a situation—usually acute situations dictating short-term use—calls for some heavy-hitter oils (i.e., dermal irritants and mucus membrane irritants and sensitizers). Here, we can call upon more gentle EOs and base products to offset (buffer) the potent components in the “heavy hitter.”
- Mostly applies to the dermal and internal routes. An example would be neat application of essential oils on a soon-to-be cold sore, trauma (bruising, pain), acute illness (bronchial infection, food poisoning).
- Helps off-set concerns of using “potent” or “scary” oils to some extent.
- Aligns with the idea that you won’t make something “in-active” when blending different oils together.
Let’s say I feel a cold sore coming on, which calls for heavy-hitter antiviral oils. Cymbopogon citratus would be lovely but quite irritating to tissue! I may quench that with Santalum ssp. and/or Melaleuca quinquenervia and cooling skin soothers like Copaifera officinalis or Vetiveria zizanoides to round out the blend. Furthermore, I may add a small amount of an anti-viral fixed oil to add emollient qualities and enhance penetration.
After you have direction on why you are blending (i.e., presenting issue) it is time to set an intention to help guide your selection of EOs whilst being mindful of safety and contraindications. True, it is a best practice to always reference known therapeutic actions and applications but always leave room for the poetry of blending. Along with synergy, additivity (“stacking”), contraindications and quenching, it is also important to consider other points when blending EOs:
- It is my observation that some oils are challenging to work with from an olfactory perspective, meaning they often don’t pair well with other oils. This is when I look to cooking and ingredient pairings: what herbs and spices go well together? Trust me, this is very helpful when harmonizing a synergy and as a default, enhances synergy. (See “Blending Ideas” below).
- Plant parts (morphology) often go well together: roots with roots, roots with seeds, flowers with seeds, leaves with resins. This is explored in our “Aromatic Scholars: Aromas & the Mind” class and chakra workshops I have led in the past.
- Blending within the same plant family is a way to familiarize yourself (e.g., make a “Lamiaceae” blend). Once you understand the nuances within the families, you get to know how one family is often known for a few key indications whereas another family excels in a different realm of healing.
- Synergies consist of 3 to 5 essential oils; increasing the number of oils starts to dilute your intention. Remember, this is not perfumery. More oils may also dilute the components (unless you are taking the “additive/stacking” approach). Have you ever combined too many colors on your palate when painting where you ended up with a dull grey? Yup.
The impetus behind this post was watching many students enthusiastically blend aromatically strong oils like fennel or ginger with other EOs and rejecting the initial blend which makes them basically reject the EO. Ay! Let’s give the oil and therefore plant a chance! Following are some tri-parings where one dominating essential oil may be complimented by two others.
Notice how many parings go nicely together when using the herbs and spices in cuisine or imbibed as an infusion (using the complete plant material). This is when SYNERGY may start to emerge—both from the olfactory sense as well as the chemical sense.
Take out your bottles of the EOs listed below and bring them together to smell each pairing directly from the bottles. If you’d like to make an actual synergy, get out a stock blending bottle and add the number of suggested drops (indicated in [brackets]) of each oil to the bottle. Then cap the bottle and leave it alone for at least 24 hours (or 3 days!) before smelling or using it—this time lapse allows the blend to settle.
|Synergy Description||Suggested Route of Admin||Essential Oils|
|Uplifting, clearing, fresh, respiratory support||Inhalation||Bay laurel (Laurus nobilis) , Grapefruit (Citrus x paradisi)  and Peppermint (Mentha x piperita) |
|Clear thinking and breathing, fresh and exhilarating||Inhalation||Rosemary 1,8 cineole (Rosmarinus officinalis CT 1,8 cineole) , Frankincense (Boswellia sacra/carterii) , Lemon (Citrus limon) |
|Moving, stimulating, flushing||Topical||Rosemary (Rosmarinus officinalis CT 1,8 cineole) , Fennel (Foeniculum vulgare var. dulce)  and Juniper (Juniperus communis) |
|Digestive and calming||Topical||Roman chamomile (Chamaemelum nobile) , Fennel (Foeniculum vulgare var. dulce)  and Sweet orange (Citrus sinensis) |
|Warming for pain||Topical||Ginger (Zingiber officinalis) , Lemongrass (Cymbopogon citratus)  and Coriander (Coriandrum sativum) |
|Moving and brightening, spasm, pain||Topical||Juniper (Juniperus communis) ,Bay laurel (Laurus nobilis)  and Clary sage (Salvia sclarea) |
|Cooling, balancing circulatory support||Topical||Cypress (Cupressus sempervirens) , Vetiver (Vetiveria zizanoides)  and Geranium (Pelargonium graveolens) |
Parting thoughts: There is a great freedom in practicing aromatherapy, especially as you get to know each aromatic plant, its essence and inherent synergism within the plant. Yet freedom rightly calls for restraint. Consider the following concepts when blending: the core issue of the individual, whether the individual enjoys the blend of essential oils chosen for them (how do the oils smell together?) and the chemistry of the oils as it relates to synergy, “stacking” and “quenching” against the individual’s constitution, health concerns and any drugs taken. It may be daunting in the beginning but this is a part of the beauty of a practice.
Author’s sidebar: I feel the milieu we live in overemphasizes “science” over “art.” In this thirst for science I wonder where all of the randomized double blind clinical trials are on essential oils that some may pine away over to “legitimize” observations people have known for hundreds of years. Have you noticed how a vast amount of research on plants and their terpene components as related to health is conducted in countries other than the USA? It is very hard to put a patent on plants and their naturally occurring substances, hence research dollars don’t pour into research for plant-based healing modalities. Also notice how if and when research is presented on an EO—or more often on specific terpene components—it is often qualified with: “more research is needed”? The serpent keeps biting its own tail.
1Note: many references I’ve seen regarding synergy in aromatherapy have a pathological view (e.g., combination of EOs effective against MRSA in vitro (i.e., aromatogram) or more-so, a focus on single chemical components, combined, to look at effects in vitro. How is this directly comparable to a lived, messy, human experience?
2https://www.smithsonianmag.com/science-nature/why-hamsters-cannabalizing-their-young-180968071/ (Accessed 3/8/2019)
3Methyl salicylate: https://www.drugbank.ca/drugs/DB09543 (Accessed 3/18/2019)
4This isn’t to say that it still behooves the practitioner to reference safety data and to always use a conservative and “first do no harm” approach!
5The cases where cells are treated in vitro with “active components” or laboratory animals are subject to high doses of a component for an extended period that would not occur in the daily life of an average homo sapien.
6Although there are many arguments for working with whole substances, I am fond of select passages from Buhner’s book (pgs. 208 & 226). Buhner, Stephen Harrod (2002). The Lost Language of Plants: The Ecological Importance of Plant Medicines to Life on Earth. White River, VT: Chelsea Green Publishing.
7Pharmacodynamic interaction: where drugs influence each other’s effect directly. Synergy from this perspective, when the effect is desirable, is seen as molecules mutually potentiating effects in the same direction. The example in a meta-review (cited in this foot note) is of anti-infective and pain therapy. Interesting to note how essential oils excel in these two instances. Citation: Cascorbi I. (2012). Drug interactions–principles, examples and clinical consequences. Deutsches Arzteblatt international, 109(33-34), 546-55; quiz 556.