I've been getting questions on my Facebook Group "Essential oils and internal use" about what scientific research there is on the safety and efficacy of ingestion of essential oils. As a starting place, I tried a search in PubMed, but came up with too many references to nano-encapsulation methodology. 

So then I thought I would go into my EndNote library which I've been saving references into for about 20 years, and search for the word "capsule". About 50 articles turned up, so I've made a bibliographic list of these, plus a table summarising the oils or constituents used in the capsules, and the conditions the encapsulated oils were used for (see PDF at the end of the article). The list is not an exhaustive list of the research on trials using ingested encapsulated essential oils, but it gives you an idea of the trials available. In addition to my reference list, p. 50 of "Essential Oil Safety", by Tisserand & Young (2014) lists trials on: Cinnamon Bark for loss of appetite; Geranium oil for stress and hypertension; Juniperberry oil for dyspepsia; Oregano oil for intestinal parasites.

Some of the products like GeloMyrtol, Tavipec, Silexan/Lasea, Colpermin and Rowachol seem to have been allowed onto the market without very much in the way of clinical trial evidence. I imagine they are formulations firstly developed in herbal medicine and phytotherapy, which, being known to be effective, were allowed to be sold as over-the-counter preparations, much in the same way as Vicks Vaporub and TigerBalm muscle rub. In particular, I'm curious that there doesn't seem to be much work done to determine the minimum effective dose, but rather the dosages used range from 80 mg to 1200 mg of essential oil per capsule without discussion of why those quantities had been chosen. The reported benefits of the essential oil capsules appear to be moderate to good improvement of symptoms (though I wonder about publication bias, and the non-reporting of non-effective treatments). Most of the clinical trials on the list mention adverse events, if there were any, and mostly these are limited to burping, nausea and mild stomach pain. 

What we need to feel confident in safe and effective internal use of essential oils is some careful research to determine the therapeutic window for each oil (and for each condition we are using the oils for). Unless we use high enough dosages, we are unlikely to see much effect (beyond perhaps a placebo effect), but if the doses are too high (or repeated too frequently or for too long), we are likely to start seeing adverse events. And for most oils, we don't know how much EO must be ingested for which effect, or at what dosage level people are likely to experience adverse events. 

Herbalists, phytotherapists and aromatic medicine practitioners are more likely to be able to recommend dosages that may be effective, but even they are experimenting, as we don't have clinical studies on enough people. There is nothing stopping someone from experimenting on themselves and possibly finding much benefit, but there is not enough evidence yet for us to know what are the safe AND effective internal dosages for most of our essential oils. In my opinion, the likely risks of toxicity and ill-effects of long-term internal use are too high to warrant the home-use of essential oils in capsules, unless under medical supervision. Unless you want to offer your body to science... in which case, please document the treatment and the results and let us know!!

If you are a teacher, blogger, or writer, you probably use information gained from other people's writing. It is important to let your students and readers know where you got your information from, which is called "referencing" or "citing". Your references should be detailed enough to allow other people to find the original source documents you used. Referencing is courteous, and adds credibility to your work. If you quote directly from someone else's work, you must use quotation marks, and reference your source, or else it is plagiarism - passing off someone else's work as your own.
The citation is the bit that looks like (Bowles, 2020), the reference contains the full details of the information source: Bowles, E. Joy, (2020), "Dr Joy's Aromatherapy", Diem Capta Books, Australia, and is usually located at the end of the document (or in footnotes at the bottom of the page). Often the words "citation" and "reference" are used interchangeably.
Referencing StylesThere are many academic referencing styles in use. A referencing style refers to the way the citation and reference details are formatted, for example using full names, or just initials, using italics or bold for the title of the work, and what order the authors, dates, titles, and publisher details are listed.
A common referencing style is the American Psychological Association (APA) style. Here is a link with examples of how to cite every type of information source, including webpages, books, journals, and newspapers in the APA style. Murdoch University Library (2021) "Help and Support: APA - Referencing Guide: All Examples", https://libguides.murdoch.edu.au/APA/all, accessed 21 Feb 2021.
While you can add all your references for each article manually, it is better to use a reference or citation manager program. As it is likely you will want to use references more than once, a reference manager saves time. Here is an article comparing four of the better-known programs, two of which are free (Ivey & Crum, 2018). For ease of access, here is the link to the free PubMed Central version https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6013132/ but the proper APA reference to the article is below:
Ivey, C., & Crum, J. (2018). Choosing the Right Citation Management Tool: Endnote, Mendeley, RefWorks, or Zotero. Journal of the Medical Library Association: JMLA, 106(3), 399–403. https://doi.org/10.5195/jmla.2018.468
Using a reference/ citation managerWhen you find information you want to cite, you can either import an existing reference into the citation manager (often on the page with the academic article), or create a new reference yourself. A data-entry form in the citation manager opens for each type of information source, and you type in the required details and save it. The reference will be added to your personal library of references accessible by the citation manager, either on your computer, or in the ‘cloud’.
The citation manager programs have add-ons for Word which allow you to insert the reference and citation as you type your document. When you have finished, you can choose which referencing style you would like, and the program will automatically format your citations in that style.
As a final tip, if you are citing information from a review article, it is best to go to the original article cited in the review if you want to quote data or results, as sometimes the review article does not provide sufficient information, or only partly reports on the original data. But you can also create a citation like this:  Jaen & Dalton (2014), as cited by Bowles (2020), and the reference in the list at the end would be Bowles, E. Joy, (2020), "Dr Joy's Aromatherapy", Diem Capta Books, Australia, p. 26

To cite this blog-post use this: Bowles (2021), Bowles, E. Joy. (2021, February 21). Why and how you should reference other authors' work. Dr E. Joy Bowles' Blog. https://www.ejoybowles.com/blog#/

​Many questions from people in DoTerra or Young Living who are concerned about taking essential oils internally... The question to ask is - please show me the CLINICAL research that shows ingestion of oils like this is SAFE and EFFECTIVE. 
My comments are these: if you are a healthy adult who is not taking any medications or other herbal/ vitamin supplements, and you put one drop of an essential oil into a glass of water, and drink it, the worst that is likely to happen is that your lips, tongue, mouth and throat will be irritated by the oil and you will experience pain for about 20 minutes (perhaps longer), that will reduce if you drink a glass of full-fat milk afterwards. Oil doesn't dissolve in water, but the fat in the milk should help remove the essential oil from the tissues. 
If you repeat this several times in a day, you will be consuming more of that essential oil than you would ever likely consume in food or drink in one day, and although the essential oils are given GRAS status (Generally Recognised As Safe), this only means Safe at the levels consumed in the average American diet. In other words, we actually don't know for sure if ingestion of essential oils as recommended by those companies is SAFE. We also don't know the effects of taking essential oils every day for several weeks, months or years. The research has not been done... yet... 
My main concern is when essential oils are taken by people who have serious diseases, and who are taking other drugs, or who are children or elderly. Because essential oils have to be processed by the liver and kidneys, like other drugs, there is a chance for 1) alteration of the function of the other drugs that the person is taking 2) increased toxicity of the essential oils or the other drugs because the liver can be overwhelmed by having to process so much 3) we don't have the evidence that ingested essential oils are safe in combination with other drugs, or in people with serious disease (cancer, hepatitis, diabetes, cardiovascular disease, asthma, clinical depression). 
The question to ask is - please show me the CLINICAL research that shows ingestion of oils like this is SAFE and EFFECTIVE.

This was a story related to me in August 2018, by an aromatherapist friend and her partner who have been using essential oils for many years for many different purposes. The man is in his 60s, and generally a fit and strong man, an ex-Vietnam veteran, who has been taking anxiolytic medication to help him manage his Post Traumatic Stress Disorder.
They decided to trial a herbal sleep remedy with Lavender oil in it that was supposed to help promote restful sleep, and added a couple of capsules to his medication one evening, as he was not sleeping well.
The morning after taking the herbal sleep capsules this is how the man described his experience:
 
After waking up following voiding of my bowels in bed:
 (1) I tried to get out of bed as I felt unclean.
 (2) I could not stand up properly and crashed to the floor. I lay on the floor for several minutes, until I could gather my strength and stand up. By this time my partner helped me up and gave me directions to the shower.
 (3) When I was wobbly before I crashed to the floor, I vaguely remember vision problems as I could not orientate myself between the bed and the side dresser and I was quite dizzy. I had to confirm where I was by touch. I took a few wobbly steps and crashed to the floor at the end of the bed. I lost all strength to my knees and collapsed. [This is all very embarrassing to me as I consider myself a Rock and a strong man].
 I cannot recall my state the next morning, as from memory, I felt quite crook and stayed in bed until early pm that day.
 
His usual medication regime, most of which are S4 prescription medications, with extensive warnings, is as follows:
Escitalopram; Seroquel; Imovane; Apo-risperidone (full details of dosage in attached PDF, see below).

The capsules contained the following:  Lavender essential oil and L-Theanine along with lemon balm, passionflower, and chamomile (dosage not given; preparation not stated for the last three ingredients, whether herbal powder or essential oil).
The list of reference papers given by the capsule company supporting the use of these ingredients is also in the attached PDF, and I’ve found out what the dosage was in each of the papers, so the dosage in the capsules was probably something similar.

The suggested dose for the herbal sleep capsules was 2 capsules a night, which would “deliver the recommended dose” of Lavender essential oil, presumably either 80 mg or 160 mg. This dosage was found to be equivalent to Lorazepam in reducing anxiety if taken over 8 weeks (Woelk & Schläfke, 2010). Linalool, the main constituent in Lavender oil (about 42%) has been shown to potentiate GABAA receptors, producing a similar effect to benzodiazepines in vitro (Milanos, Elsharif, Janzen, Buettner, & Villmann, 2017).

These two papers were what alerted me to the possibility that perhaps the Lavender oil in the capsules may have interacted with the mixture of drugs already in the man’s system, to exacerbate the dizziness side-effects.  I don’t know what would have caused the nocturnal voiding of the bowels while he was asleep, however.
​
I think the event was a drug interaction between the components of the herbal sleeping capsules and the man’s existing medication, and that people taking S4 drugs should take care when taking oral dosages of Lavender essential oil, as there may well be unexpected drug interactions such as the ones reported here.
References
Bradley, B. F., Brown, S. L., Chu, S., & Lea, R. W. (2009). Effects of orally administered lavender essential oil on responses to anxiety-provoking film clips. Hum Psychopharmacol, 24(4), 319-330. doi:10.1002/hup.1016
Chang, S. M., & Chen, C. H. (2016). Effects of an intervention with drinking chamomile tea on sleep quality and depression in sleep disturbed postnatal women: a randomized controlled trial. J Adv Nurs, 72(2), 306-315. doi:10.1111/jan.12836
Fißler, M., & Quante, A. (2014). A case series on the use of lavendula oil capsules in patients suffering from major depressive disorder and symptoms of psychomotor agitation, insomnia and anxiety. Complement Ther Med, 22(1), 63-69. doi:10.1016/j.ctim.2013.11.008
Higashiyama, A., Htay, H. H., Ozeki, M., Juneja, L. R., & Kapoor, M. P. (2011). Effects of l-theanine on attention and reaction time response. Journal of Functional Foods, 3(3), 171-178. doi:https://doi.org/10.1016/j.jff.2011.03.009
Juneja, L. R., Chu, D.-C., Okubo, T., Nagato, Y., & Yokogoshi, H. (1999). L-theanine—a unique amino acid of green tea and its relaxation effect in humans. Trends in Food Science & Technology, 10(6), 199-204. doi:https://doi.org/10.1016/S0924-2244(99)00044-8
Kakuda, T. (2011). Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction. Pharmacol Res, 64(2), 162-168. doi:10.1016/j.phrs.2011.03.010
Kennedy, D. O., Scholey, A. B., Tildesley, N. T. J., Perry, E. K., & Wesnes, K. A. (2002). Modulation of mood and cognitive performance following acute administration of Melissa officinalis (lemon balm). Pharmacology Biochemistry and Behavior, 72(4), 953-964.
Kimura, K., Ozeki, M., Juneja, L. R., & Ohira, H. (2007). l-Theanine reduces psychological and physiological stress responses. Biological Psychology, 74(1), 39-45. doi:https://doi.org/10.1016/j.biopsycho.2006.06.006
Milanos, S., Elsharif, S. A., Janzen, D., Buettner, A., & Villmann, C. (2017). Metabolic Products of Linalool and Modulation of GABAA Receptors. Front Chem, 5, 46. doi:10.3389/fchem.2017.00046
MIMS/myDoctor. (2017). Medicine Finder.   Retrieved from https://www.nps.org.au/medical-info/medicine-finder/
Ngan, A., & Conduit, R. (2011). A double-blind, placebo-controlled investigation of the effects of Passiflora incarnata (passionflower) herbal tea on subjective sleep quality. Phytother Res, 25(8), 1153-1159. doi:10.1002/ptr.3400
Nobre, A. C., Rao, A., & Owen, G. N. (2008). L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr, 17 Suppl 1, 167-168.
Scholey, A., Gibbs, A., Neale, C., Perry, N., Ossoukhova, A., Bilog, V., . . . Buchwald-Werner, S. (2014). Anti-stress effects of lemon balm-containing foods. Nutrients, 6(11), 4805-4821. doi:10.3390/nu6114805
Woelk, H., & Schläfke, S. (2010). A multi-center, double-blind, randomised study of the Lavender oil preparation Silexan in comparison to Lorazepam for generalized anxiety disorder. Phytomedicine, 17(2), 94-99. doi:http://dx.doi.org/10.1016/j.phymed.2009.10.006

By E Joy Bowles, PhD, BSc Hons.
As a scientist, I have mixed feelings about the way scientific research is being used to support the claims for essential oil use. On the one hand, I am delighted that essential oil users are curious about how their oils work, and are keen to seek out more information. On the other hand, I am alarmed that they are happy to settle for summaries of research and claims made in abstracts without going to the source articles or reading the full papers to double-check the claims made.
As an example, two papers have come to my attention recently, both posted on Facebook by well-meaning essential oil enthusiasts.
 
Valid or invalid: exposure to essential oils for more than 1 hour may be harmful to cardiovascular health?
A report in the European Journal of Preventive Cardiology “The effect of essential oil on heart rate and blood pressure among solus por aqua workers” published in 2014 claims in the abstract “Prolonged exposure for longer than 1 hour to essential oils may be harmful to cardiovascular health among spa workers”. The person posting it on Facebook was alarmed, and wanting to caution their friends about using essential oils safely.
 
Their trial involved 100 healthy young spa workers inhaling vaporised Bergamot oil over a 2-hour period, and having their blood pressure taken every 15 minutes. The experiment was repeated 3 times, and there were no statistically significant results between the results from each occasion. Initially participants experienced a small decrease in mean systolic and diastolic blood pressure and pulse rate, but in the measurements taken during the second hour of the experiment, they experienced a small increase in means for these measures, compared to baseline. The mean decrease in systolic BP was -2.1 mmHg (at the 45-minute measure), the mean increase was + 2.19 mmHg (at the end of the 2 hours).  
 
However, there was no control group, so there is no way of knowing whether the changes in BP were due to the Bergamot oil, or not. Conceivably, people’s BP could drop just by sitting still for 45 minutes, and could rise again as they got stressed by being bored during the second hour!
 
In their discussion, although they acknowledge that “it is still unknown whether small, short-term fluctuations of BP and HR are associated with a higher risk of clinical cardiovascular diseases even if elevated BP and HR can serve as markers for increased risks of cardiovascular diseases”, they go on to make their unfounded statement that prolonged exposure may be harmful to cardiovascular health.  And the title and abstract claim the research is about “essential oils” in general rather than Bergamot essential oil specifically.
 
So, in my opinion, the conclusions are invalid, and the article should not be shared as evidence of effects of essential oils on human health.
 
Valid or invalid: Essential Oils can help ADHD?
The other shared article titled “Essential Oils Can Help ADHD” posted on the internet by osteopath Dr Joseph Mercola claims that “Research by the late Dr Terry S. Friedmann, a physician who believed in treating the body, mind and spirit as one, showed that vetiver oil was beneficial for children with ADHD.”
On reading the paper by Dr Friedmann (not from a peer-reviewed scientific journal, just from a Meetup website), it turns out that Dr Friedmann’s conclusions about vetiver were based on 4 subjects only, and fails to mention whether the changes in beta-theta wave ratio that he observed were measured while the subjects were being challenged with a task requiring focused attention or not. Dr Friedmann also fails to comment on the fact that the 16 children in the control group (who had no essential oil treatment) also experienced positive changes in their beta-theta wave ratios. It is not valid to make claims of a generalisable therapeutic effect based on results from just 4 subjects.

The other papers Dr Mercola cites as possible evidence for Vetiver being good for ADHD are from an experiment done on sleep-wake hours in rats exposed to vaporised vetiver oil, and one done on alertness of 18 adults without ADHD exposed to vapour from fresh roots of vetiver, not the essential oil!

It would be great if there really was evidence that inhaling essential oils had measurable effects on focus in children with ADHD. However, none of these articles provide sufficient evidence for me. I would not share any of these articles as evidence that essential oils help ADHD.

How to determine quality of a scientific paper
To determine the quality of a scientific paper, two things need to have been done: firstly, the trial needs to have been designed and carried out appropriately; secondly, the report needs to contain sufficient detail for readers to be able to fully understand the trial design, results, discussion and conclusions, including any limitations noted by the authors.
Essential oil users wanting to find out if a scientific paper provides real evidence to support therapeutic claims for an essential oil need to become “quality detectives”. The first question to ask is “Is the full-text available anywhere, rather than just the abstract?” Try Google Scholar or Research Gate, https://www.researchgate.net/ where a lot of researchers publish pre-print versions of their articles.
Once you have the full-text ask these questions:

• Does the report clearly identify the nature of the participants (including age, sex, health condition measures, any inclusion or exclusion criteria)
• Was there a control group who had everything done to them in the same way, except having the essential oils, and was there also a no-treatment group who were only measured at the start and the end?
• How many people received the treatment? If it was fewer than 30 people, it’s unlikely the results can be generalised. Preferably there should be at least 100 people receiving the treatment, especially if the effect size of the treatment is small.
• Were baseline measures taken, and were the descriptive statistics of each of the groups of people in the trial the same (mean, standard deviation of the mean, range and distribution of values), or at least not significantly different when compared statistically?
• Is the dose reported adequately?
• Is there a listing of the botanic name and percentage of essential oil constituents in the oil(s) used in the trial?
• Were the tests or scales used the best ones that could have been used (gold standard, or at least widely accepted and used in medical/ nursing research?)
• Do the results make sense clinically, if it’s a clinical effect being researched? A statistically significant result does not necessarily mean a clinically significant result (as in the second paper discussed above).
• When you read the paper and look at the results tables, are there any unanswered questions you have about how the trial was done, and what the results really mean?

The need for rigour in design and reporting applies to all forms of scientific research, not just complementary therapies research. The CONSORT group (CONsolidated Standards Of Reporting Trials) is an independent body of researchers that has developed checklists and guidelines for researchers to use to ensure their research design and reporting is of good quality. There are several variants of the original CONSORT statement, including one on non-pharmacological treatments (which aromatherapy trials usually fit into).
​
My dream is to have people using essential oils become scientifically literate enough to critically evaluate scientific papers themselves. Maybe we could start a journal club, where we go through various papers on aromatherapy/ essential oils and critique them as a group?
​Please contact me if you’re interested @DrEJoyB or [email protected]