20 | New Scientist | 20 November 2021News
Analysis Mental healthIS PSYCHEDELIC medicine finally
ready to live up to the hype? Last
week, promising results were
announced from the largest
clinical trial of psilocybin for
depression to date. They suggest
that, while psilocybin therapy is
far from a panacea, it can help
some people for whom current
medicines are ineffective.
The study was led by
Compass Pathways, a UK-based
company that holds patents for
two synthetic formulations of
psilocybin, the active ingredient
in magic mushrooms. It involved
233 people with treatment-
resistant depression, meaning
to be eligible they had to have
tried two other treatments
without success.
The participants were randomly
assigned one of three doses of
psilocybin: 1, 10 or 25 milligrams.
The 1 milligram dose is
considered so small that it is
effectively a placebo, but it meant
that all participants knew they
would get psilocybin, creating
an expectation of some benefit.
All were given psychological
support before, during and
after a single dosing session.
In the 25 milligram group,
36.7 per cent of patients hadimproved depression severity
scores three weeks after their
dose, and 24.1 per cent were
still responding after 12 weeks.
These numbers may seem low:
in another trial published earlier
this year, 70 per cent of patients
who received psilocybin therapyshowed a response at six weeks.
But that study was smaller and
involved two doses of the drug.
“There is a general trend in
science that the first small studies
have huge effect sizes, and as you
study more, they get less and less.
The hope that we all have is that
it doesn’t disappear,” says Allan
Young at King’s College London,
who worked on the Compass
Pathways study. “We need to
do a lot more work looking at
the duration of the effect and
see how it pans out in the clinic,
but the fact that a group has a
persistent benefit to 12 weeks,
to my mind, is really heartening.”
The contrast with conventional
antidepressants is stark. People
usually need to take daily pills forseveral weeks before seeing
an effect, and if they stop taking
them, they risk relapsing.
Psychedelics present an
alternative approach. Young
suggests people may have a
one-off treatment, see a benefit
that lasts for weeks or months,
then return for occasional top-up
treatments if needed.
Depression affects an
estimated 264 million people
worldwide, many of whom don’t
benefit from existing treatments.
As a result, there is a real need for
alternatives, especially ones that
lead to fast results.
A form of ketamine, a drug
with psychedelic effects but a
different mode of action, has
already been approved by the US
Food and Drug Administration
(FDA). Backed by a growing
number of pharmaceutical
companies and non-profit
organisations, psilocybin looks
like it could follow.
A trial led by the Usona Institute
in Wisconsin involving 100 people
with major depressive disorder
is due to report results next year.
Compass Pathways plans to begin
the final stage of its clinical tests
in 2022, and the FDA has already
designated it a “breakthrough
therapy”, which could accelerate
the approval process.
Taken together, these
developments suggest
psychedelics could soon be
seen as credible mental health
treatments, at least for some
people. “We have to be cautious
about overpromising, because
they don’t work for everyone,”
says Celia Morgan at the University
of Exeter, UK. “I think they will
provide a really important and
novel contribution to psychiatry.” ❚COMPAS
S^ PATHWAYSInside a therapy
room used in a clinical
trial of psilocybinPsilocybin steps closer to credibility Promising results
suggest that psychedelic therapies could help some – but not
all – treatment-resistant depression, reports Sam Wong“ We have to avoid
overpromising, because
psychedelics won’t
work for everyone”AnimalsJake BuehlerBARN owls are one of the most
widely distributed birds, being
found on six continents. In Europe,
they follow a general pattern:
southern areas host pale owls
and darker birds dominate in the
north. But barn owls in the British
Isles are consistently a stark white,
and a new analysis explains why.
Ana Paula Machado studied
the owls (Tyto alba) while at
the University of Lausanne
in Switzerland. She and her
colleagues analysed DNA from
147 barn owls across six European
populations. In particular, they were
looking for evidence that owls on
the British Isles had dark-feathered
ancestors and then underwent
strong selection for pale feathers.
They didn’t find any.
“We didn’t see that one
coming,” says Machado, so they
began looking for an alternative
explanation. She and her colleagues
used data on the habitats that barn
owls occupy today to predict how
they would have been distributed
across Europe under ancient
climatic conditions. This revealed
a now-submerged land corridor of
suitable owl habitat along the Bay
of Biscay, bridging Iberia and the
British Isles some 20,000 years ago
(Molecular Ecology, doi.org/g5mg).
This suggests owls in the British
Isles had pale-feathered ancestors
from southern Europe – an idea that
fits with the genetic evidence. ❚Why barn owls
in the British Isles
are ghostly whiteSH
UT
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/ON
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White barn owls in the
British Isles are related
to similar birds in Portugal