tDCS course Chapter 6 Safety of tDCS - #29 - July 13, 2025

Mike: 00:00:05

Welcome back to the Neurostimulation Podcast.

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Now we're going to explore chapter

six in the textbook that we've been

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reviewing called Practical Guide to

Transcranial Direct Current Stimulation,

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Principles, Procedures, and Applications.

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In chapter six, we're going to unpack

the latest findings in tDCS safety

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in both human and animal studies.

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We're going to break myths down, and

we're going to highlight the current

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best practices for risk management in

both clinical and research settings.

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So let's look at the framework for

safety evaluation first of all.

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a foundation really is that this

particular chapter in our textbook builds

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upon the 2016 tDCS safety consensus and

follows the World Health Organization's

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definitions, distinguishing between

so-called adverse events, which are

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incidents that might be coincidental

and adverse effects, which are incidents

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that are causally linked to tDCS.

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So what's the gold standard of concern?

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Serious adverse effects, which could

include things like brain tissue injury,

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lasting functional impairment or adverse

outcomes that lead to hospitalization or

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death, causally linked to stimulation.

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Notably, temporary sensations like

tingling, itching, or mild headaches

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don't count under this strict

definition of safety, those are

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considered to be tolerability issues.

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So what the evidence tells us across

more than 33,000 tDCS sessions and

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over 1000 individuals in formal

trials, there has been zero evidence

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of irreversible brain injury.

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There's been no causal link to things

like seizures or hospitalizations

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due to conventional protocols at

around, less than or equal to 40

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minute sessions at less than or

equal to 40 milliamperes of current.

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Animal studies are backing this up.

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Even when tissue damage was observed

in animal models, it only occurred

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at stimulation levels and order

of magnitude higher than what's

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used in clinical tDCS in humans.

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So for conventional tDCS, safe

by all evidence-based measures.

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Now let's look at how risk is

assessed in animals and humans.

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Animal data is used to establish

a damage threshold by identifying

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the lowest current level that

causes histological brain injury.

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Histological is a technical term that

refers to injury that's observable

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at the level of the brain tissue.

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So if you were to take, um, in the lab,

if you were to take, uh, a brain, a

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cadaver sample of a brain that's been

donated for research and you're to do a

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thin slice and have a look at the actual.

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Brain tissue itself.

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Then histological damage relates

to what you can see either with the

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naked eye or with a microscope that

relates to the actual tissue sample.

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Researchers avoid using oversimplified

summary metrics like total electrical

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charge or charge density unless the

mechanisms of injury are well understood.

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Why is that?

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Well, it's because metrics like

charge can obscure important

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interactions between things like time,

electrode size, and brain anatomy.

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In humans, controlled trials

use predefined stopping rules

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to err on the side of safety.

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For example, in epilepsy studies,

trials are paused if seizure frequency

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increases by a set percentage, even

if the link to tDCS is not confirmed.

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What about vulnerable populations?

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Let's look at some key populations

where safety concerns often arise.

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Current modeling is suggesting

different current flow patterns due

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to the smaller skulls in children,

but no adverse effects reported when

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using age appropriate protocols.

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What about stroke survivors?

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Out of over 500 participants across

33 stroke studies, only 14 have

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dropped out, and none were due to

serious tDCS related adverse effects.

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How about epilepsy?

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There were no reported

seizures caused by tDCS.

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In fact, cathodal tDCS may

actually have an anti epileptogenic

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effect, an anti-seizure effect by

reducing cortical excitability.

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What about people with brain implants,

skull plates, or other cranial implants

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are excluded from some studies, but

this is often precautionary, not because

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there's any proven increased risk.

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Now let's look at is home tDCS safe?

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The short answer, yes.

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If it's done right and under supervision,

clinical trials involving home use of tDCS

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have shown no serious adverse effects when

using medical grade regulated devices.

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High compliance and tolerability when

combined with telehealth supervision

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and proper caregiver training.

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One patient with schizophrenia

even completed over: 1000

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sessions over three years

without any serious side effects.

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The takeaway message, home use is

safe if protocols are followed.

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What are some common

concerns and misconceptions?

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Now let's tackle some myths.

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Myth number one, tDCS has

not been tested long enough.

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In reality, multiple clinical trials with

over 100 sessions in certain individual

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patients spanning months to years

shows no evidence of cumulative harm.

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Myth number two, it's

dangerous for older adults.

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In reality, 600 plus older adults have

safely participated in tDCS trials

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with no serious events reported.

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Myth number three, it could

cause permanent brain damage.

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In reality, lasting neuroplasticity is

part of the goal, but without meeting

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the strict criteria of tissue injury

or lasting dysfunction, such changes

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don't qualify as safety concerns.

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In fact, they likely relate to the

positive effects of this technology.

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The chapter of the textbook cautions

against unscientific alarmism, and it

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calls for caution based on speculation

rather than evidence, which may

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actually impede research progress.

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Now let's look at what could potentially

go wrong and how we can avoid that.

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Mild adverse effects can happen.

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Things like skin irritation

under the electrodes.

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Tingling or mild discomfort

under the electrodes and

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temporary fatigue or sleepiness.

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Most of these mild side effects are due

to things like poor electrode preparation.

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For example, if it's a sponge type

electrode, if there is an inadequate

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amount of saline solution or gel so

that the sponge is is overly dried out.

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It could be related to improper placement

or montage of the electrodes on the

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scalp, and it could be potentially

related to usage errors in other off-label

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or DIY type knockoff applications.

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The fix here is standardized training,

quality medical grade equipment,

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and good skin contact techniques.

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Now let's consider some final safety

guidelines and map out the road ahead.

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So what are the real world

safety takeaways here?

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We need to be looking at conventional

tDCS parameters less than or

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equal to 4 mA, less than or

equal to 40 minutes per session.

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These are evidence backed and safe.

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Serious adverse effects are

extremely rare and causally unproven.

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Home use is safe under supervision

and vulnerable groups can be safely

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included with tailored protocols.

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However, vigilance is still important.

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It's important to use ethics research

board approved protocols in studies

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to maintain clear stopping rules and

also to track all events carefully.

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Future safety updates will likely

come from larger long-term data sets.

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Better real-time monitoring and

integration with biomarkers of risk.

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So in closing, when it's applied

responsibly, transcranial direct

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current stimulation appears to

be one of the safest forms of

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neuromodulation currently available.

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It offers a compelling

combination of accessibility.

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Portability, low cost and safety,

all backed by thousands of

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sessions and robust research data.

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Thanks again for tuning in.

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I really appreciate your time,

your attention, and your curiosity.

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If this helped to clarify any doubts that

you might have had about tDCS' safety,

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please share this with colleagues,

patients, anyone that you think might

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be interested in learning more about

this technology, don't forget to like

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sure that you never miss an episode,

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please leave a review, a question or

a comment in the comment section below

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as well as any suggestions for topics that

you'd like us to cover in future episodes.

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So until next time, don't forget to

tune into the next episode of the

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Neurostimulation Podcast and we'll

see you there In the meantime, take

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care, be well, and stay curious.