some MYTHS removed

©  By M. Watt 1994. Revised 2006
First Published by The Aromatic Thymes Vol. 3 No.4 1995. pp22-30

A lot of misleading information has been published for many years about
commonly occurring "toxins in plant medicines." This has not only occurred in
the media, but also in many scientific publications. I have been studying the
literature relating to the toxicity of medicinal plants over many years.
Therefore, I am aware that as much myth and superstition is promoted by
members of the medical and science professions, as by people working in so
called 'complementary medicine.' The Publics safety is put at risk by the
promotion of such myths.

I have chosen Pennyroyal as my subject as it is a classic example of incorrect
information leading to deaths and severe illness.

Some Herbalists, most Aromatherapy organisations and authors (actively
supported by science professionals), have been very active in promoting myths
about the dangers of these plants and their oils. If it were not for them, then
the incidence of women who have poisoned themselves in vain attempts to
procure abortions would have been substantially lower.

I feel this article may trigger a flood of people claiming the use of pennyroyal
has been an effective abortificacient. However the evidence is clear, no such
physiological action exists.
We should never of course forget that the most
powerful mechanism influencing what happens in the body is the mind. If
someone takes pennyroyal and strongly believes it will work, then it may well
do, but it is not directly due to this wonderful oil.

The following investigation was an effort to put into context statements made
by some researchers about naturally occurring plant toxins. The claims made
about plant toxins are frequently greatly exaggerated. Potential hazards are
rarely (if ever) weighed against the huge amounts of harm caused to human
health and the environment by synthetic chemicals and their eco-persistent

There is a great deal of concern about synthetic oestrogenic chemicals. Some
scientists believe these may be responsible for the significant decline in male

An alarming report has proved that high levels of pesticide residues are found
in human breast milk. P. M. Quinsey et al. 1995. Food Chem. Toxic. vol. 33,
No. 1, pp 49-56.

It is therefore vital to remember, that these synthesised chemicals have been
tested and declared safe by scientists working on behalf of various regulatory
authorities. Due to this, we should be asking very hard questions about the
methods these scientists have used to ascertain safety. We should also ask if
these same people can be trusted to accurately evaluate potential hazards
from natural toxins in plants.

One thing I say to students in my classes is "certainly some chemicals
occurring in plants can easily kill you. However if they do, at least the
chemicals concerned are environmentally friendly by biodegrading along with
your body”. This is totally different from toxic residues from many man-made
chemicals. Some of these chemicals can persist for many years in the
environment, and can and have harmed future generations.

(Mentha pulegium & hedeoma pulegioides varieties.)
Introduction to article:
Pennyroyal oil is frequently quoted as being “dangerous for use during
pregnancy”. Yet, the documented cases of human poisoning via attempts to
induce abortions find scant evidence of such an action. Medical textbooks from
the turn of the century state that "attempts to procure abortions using
Pennyroyal were rarely successful" Cushny. Pharmacology & Therapeutics

The consumption of several millilitres of pennyroyal oil is highly likely to cause
toxic effects. However, the dose needed to cause death (around 20 grams), is
similar to the amount required by a common over the counter drug
paracetamol (UK name). There are thousands of cases of paracetamol
poisoning each year from far lower doses - mainly from self overdose. Despite
these statistics, little significant policing has occurred on the volumes that can
be sold in.

Authoritative proof that Pennyroyal oil used in sensible amounts is not
toxic or hazardous exists as follows:

Toxicity levels:
The oral LD50 in rats is reported to be 0.22-0.58 g/kg. (average 0.4). O.
Moreno 1973. Reports to the R.I.F.M.

d-pulegone was classified as a permitted food additive by The Council of
Europe in 1974. In annex 11-426 it is allowed in beverages at 250 mg. per kg.
and in mint confectionery at 350 mg/kg. Therefore, eating 100 grams(4
ounces) of pulegone flavoured confectionery would provide the equivalent of
35 mg. of pulegone or nearly 2 drops of the oil (assuming a pulegone
content in the oil of 70%).

The UK Food 1992 statutory instrument, still permits these levels of use for
food flavourings. It is unlikely that regulatory authorities would permit these
volumes if there were any sound evidence of abortifacient activity. There are
no warning labels suggesting that a pregnant woman does not consume
peppermints to ease morning sickness, or on mint flavoured drinks,
toothpastes, mouthwashes, etc.

Effects via the skin:
The dermal LD50 in rabbits is 4.2 g/kg. O. Moreno 1973. Reports to the
R.I.F.M. Low dermal toxicity must indicate that very little oil is getting into the
blood through the skin of animals, and almost certainly far lower levels from
dermal absorption in humans.

A 6% solution of the oil has been tested on the skin of humans, and at that
level no sign of irritation or sensitisation occurred. A. Kligman 1973. Reports to
the R.I.F.M.
Note: This lack of adverse reactions can indicate low dermal absorption. 6% is
far in excess of what is used for a routine massage.

A 10% solution of d-pulegone (which constitutes 60-90% of the oil), was
tested on humans and produced no sign of adverse effects. It was found only
poorly absorbed after it was applied to Guinea pig skin for 2 hours. F. Meyer
1965. Br. Patent 1,001,949. Therefore only the minutest traces with NO
toxicological significance are likely to be detected in the systemic circulation
following dermal application.

Other modes of absorption:
There is now sound evidence that significant levels of some fragrance
chemicals can enter the bloodstream via inhalation. However, if only 1 to 2
drops of pennyroyal oil were used in a massage blend, then the total systemic
intake must still be below that permitted in foods.

Deaths and poisonings:
Death has been reported after the consumption of 25 mls. of the oil, J.
Sullivan et al. 1979. J.A.M.A. Vol. 242, No. 26, pp 2873-2874. At that level of
use, it makes the toxicity of pennyroyal oil very similar to that of paracetamol,
a freely available over the counter medicine.

The relevant data for toxicity in humans comes from American reports. Large
volumes of oil were consumed in unsuccessful attempts to promote abortion,
see ref. above plus; J.A.M.A. V.241, No. 21, 2246 which appears to be based
on the same report as the former reference.

In the above reports it was stated that “one woman consumed 7.5 mls. and
another woman 10 mls. of pennyroyal oil.” They were both very ill for a couple
of days. Following treatment, both recovered fully and were discharged after a
few days. No residual liver or other discernible damage was reported
(somewhat different to the organic damage that occurs following Paracetamol
overdose). In one of these cases, pregnancy testing was positive, but it is not
reported if the abortion attempt succeeded.

d-pulegone and unreliable testing:
There are numerous research papers relating to the toxicity of d-pulegone (the
major component of pennyroyal). The vast majority are based on results
obtained from mice and rats, or from tests in- vitro on isolated tissues. Using
these kinds of tests, it is common to find assumptions being made, that
similar toxicity will occur in humans. This is despite it being known that many
natural toxins are metabolised differently in animals. We had a similar case
with Basil, where experiments on animals and men produced differences in the
metabolism of the offending substances. A. Anthony et al. 1987. Fd. Chem.
Toxic. Vol. 25, No.11, 799-806.

Most of the research on d-pulegone, has used the synthetic rather than the
natural extracted chemical. Synthesised chemicals are known for not displaying
precisely the same biochemical reactions as the natural form. This can be due
to traces of impurities, with unknown biochemical reactions, present in most
‘lab grade’ chemicals. It can also be due to significant differences in isomeric
ratios, between natural and synthetic versions of the same (in theory)

Most researchers have administered massively higher doses to animals, than
would normally be experienced by humans, and by such highly unreliable
methods as intra-peritoneal injection. The tendency has been to simply ignore
that humans and animals have different intestinal tracts. Their guts evolved
differently, partly in order to deal with plant toxins commonly present in their
respective natural diets, or to be able to exploit food sources unusable by other

Other research reports on d-Pulegone & Pennyroyal oil.
Below are just a few examples of many research papers that I have on this
subject. Most of these display irrelevant and misleading science.

In this research 300 mg./kg. of d-pulegone was administered by intra-
peritoneal injection into mice. Note: this would equate to a 70 kg. human
having roughly 21 ml. injected directly into the peritoneum.
Hardly surprising
that liver damage occurred in the mice! W. P. Gordon et al. Drug Metab. &
Disp. 1987. Vol. 15, No.5, 589-594.

Similar to the above but dose 280 mg./kg. by intra-peritoneal injection.
R. McClanahan et al. Chem. Res. Toxicol. 1989, 2, 349-355.

Intra-peritoneal injection into rats, 4 doses daily of 75 mg./kg. each dose.
Note: 300 mg./kg. of pulegone equals around 0.3 grms. of pennyroyal oil. In
this research it should be noted that "technical grade" pulegone was used
containing 2% of impurities. For testing cell metabolism isolated liver cells
were used. As there is no part of the body not under the influence of peripheral
factors such as neuronal or hormonal control, I would always question results
achieved from using pieces of isolated tissue, and then assuming identical
results in the whole living creature.
D. Thomassen et al. J. Pharm. & Exper. Therap. 1988, Vol. 244, No. 3, 825-

Damage was caused to the liver and lungs of mice with 400 mg./kg. and 500
mg./kg. into rats, by intra-peritoneal injection of the whole oil. W. P. Gordon et
al. Toxicol. & Appl. Pharmacol. 1982, Vol. 65, 413-424.

Note: this paper reports on the human death following the consumption of 500
mg./kg. equivalent to 25 ml. of the oil. What on earth is the point of giving the
same amount of oil to animals and by an unnatural route, in view of the known
data from human poisoning. What were they trying to prove?

Once again 400 mg./kg. of d-pulegone into rats stomachs daily for 3-4 days.
Note: equivalent to an adult of 70 kg. consuming roughly 28 ml. (if he survived
for the first day) again what were they trying to prove? P. Madyastha et al.
Bio. & Biophys. Res. Comm. 1985, Vol. 128, No. 2, 921-927.

There have been several reports that pennyroyal and pulegone can cause
contractions in isolated animal uterine muscle. Such proposed "evidence of
abortifacient activity" is misleading in the extreme. Common causes of
powerful uterine muscle contractions are: making love, masturbation and
breast feeding. Are scientists therefore suggesting that these activities during
pregnancy abort any properly implanted foetus? One of many examples of how
unintelligent scientific researchers can be! If such uterine contractions did
result in the expulsion of a foetus, then the chances are it is nature taking its
course and simply rejecting something that is imperfect.

It seems none of the scientific evidence presented to date can substantiate the
claimed dangers to a foetus from the occasional use of pennyroyal oil in
therapeutic amounts by internal or external means.

The fact that pennyroyal extracts have been traditionally used to induce
menstruation, cannot be assumed to be conclusive evidence of an abortifacient
activity. The non-pregnant uterus is in a completely different biochemical state
to the pregnant uterus. Once implantation of a foetus has occurred it can be
extremely difficult to shift, as was well known prior to the days of modern
abortion techniques. Additionally, the factors controlling menstruation can be
100% under psychological influences. I would suggest that the fragrance of
some plants may help unblock emotional inhibition of bodily functions.
Therefore, it can't be assumed that any direct physiological actions are
occurring from the use of extracts of this plant.

The most important hazard associated with this oil, is the potential for
accidental consumption by a child. LD50 data suggests a lethal dose of
pennyroyal oil for a child could be around 3 ml.
Note: Eucalyptus oil has killed a child following only 5 ml. and few calls have
been heard suggesting that this oil is restricted.

I would not wish this information to be taken as implying that we should all
start using pennyroyal oil for treating ailments during early pregnancy.
However, if other treatments were not working, then it appears to no more
hazardous than many other essential oils. This is provided the amount allowed
in food is not exceeded. This information only holds good for the essential OIL,
there has not been sufficient investigation of the HERBAL extract to see if it
contains water soluble chemicals which could induce abortion, although I doubt

All anecdotal and unverified reports of pennyroyal causing problems are not
dealt with in this report. This is because we have sufficient sound evidence on
which to base safety judgements. Of course if anyone does stupid things like
using any essential oil day in, day out, for months or years, then toxic side
effects are very likely. This is no different to taking numerous conventional
medicines over long periods of time.

Therapeutic uses
Pennyroyal oil is so powerful that only 1-2 drops are required for conditions
such as bronchial infections. Inhalation from hot water, or inhalation when
used in massage, is the best means of getting the oil to where it is needed.
This of course further reduces the potential systemic intake to below that
allowed in food.

The oil and herbal extract have an ancient history of therapeutic use to ease
severe menstrual pain. I have treated several patients suffering from bad
period pain by massaging the diluted oil over the uterus and into the sacral
area. By combining local massage with the inhalation of this wonderful
fragrance, pain relief has occurred within 10-15 and often has lasted for
several hours. Somehow the inhalation of this oil seems to relieve uterine
congestion, getting the flow going and thereby also helping relieve pain. It
sometimes enhances conventional analgesia when effective pain relief is not
forthcoming. Female colleagues have told me that just a sniff of this oil can
stop cramping becoming more acute.

Pennyroyal is a herb of Venus and therefore traditionally has been used to deal
with a whole variety of female ailments. It therefore seems improbable that
the plant could harm that exclusively female function of bringing new life to the

Pennyroyal oil has many therapeutic benefits which there is not enough space
to go into here, but more information can often be found in medical textbooks
published before the early 1900s.

In conclusion, perhaps the reader should ask themselves why it is, that an
essential which is a permitted food flavouring, appears on the ‘not to be used’
lists issued by aromatherapy organisations. The use of this oil by therapists
allied to those organisations would also probably invalidate their insurance.
Therefore, perhaps you should also be asking about the ability of
aromatherapy organisations to ‘set the standards’. How is it that people with
inadequate knowledge seem to be able to fool insurance companies and
education authorities into thinking that they know what they are talking about?
Vital questions for a trade setting standards within the field of health care!


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