Brain Stimulation Is Safer Than You Think New Guidelines Reveal

The Machine on Your Head Is Probably Fine

The first time a transcranial magnetic stimulation (TMS) coil is placed against a person's scalp, something strange happens. A magnetic field pulses through the skull, inducing an electrical current in the neurons below. The person's thumb might twitch. They might see a flash of light. They might feel a tap on their skin that came from nowhere. And for decades, the question hanging over every session was simple: Could this cause a seizure?

The answer, according to a major new set of international guidelines published in Clinical Neurophysiology, is almost certainly not. Not when used properly. Not even in patients taking medications that lower the seizure threshold. The risk, the authors concluded, is "low" (Rossi et al., 2020). That single word represents a shift in how we think about one of neuroscience's most powerful tools.

The guidelines, which update a 2009 consensus document, were hammered out during a conference in Siena, Italy in October 2018, and refined through April 2020. The lead author, Simone Rossi, along with Andrea Antal, Sven Bestmann, Marom Bikson, and a panel of international experts, sifted through a decade of new data. They looked at thousands of sessions. They examined new devices, new pulse configurations, and new combinations with other brain stimulation techniques. What they found should make researchers and patients breathe easier.

Why We Were So Afraid of TMS in the First Place

TMS works by generating a rapidly changing magnetic field that passes through the skull and induces an electric field in the brain. It is noninvasive. It does not require surgery. It does not involve radiation. But the idea of sending electromagnetic energy into someone's brain naturally raises alarms. The most serious potential risk is a seizure. The 2009 guidelines were conservative for good reason. Early studies had reported seizures in both healthy volunteers and patients, particularly during repetitive TMS (rTMS) protocols.

Rossi and his colleagues now argue that the risk has been overstated. They reviewed all reported seizures associated with TMS from 2009 to 2020. The numbers are striking. Even in patient populations with epilepsy or those taking proconvulsant medications, the seizure rate with conventional TMS parameters and focal coils was extremely low. The authors state explicitly that "such a risk is low, even in patients taking drugs acting on the central nervous system" (Rossi et al., 2020).

This is not a blank check. The safety depends on using standard protocols. The authors caution that novel or untested stimulation parameters could still pose unknown risks. But for the vast majority of TMS applications in research and clinical practice, the fear has outweighed the actual danger.

What Actually Changed Between 2009 and 2020

The new guidelines are not a simple update. They reflect a field that has matured. In 2009, TMS was still relatively niche. Today, it is used to treat depression, to study brain function, to map motor cortex, and to explore conditions from schizophrenia to chronic pain. The devices have improved. The protocols have been standardized. And the data set has grown enormously.

New Devices, Same Safety Profile

One of the key updates concerns new stimulation devices and pulse configurations. The 2009 guidelines were written when most TMS used biphasic pulses from standard figure eight coils. Since then, researchers have developed deep TMS coils, H coils, and devices that can deliver more complex pulse patterns. The new guidelines explicitly address these. The authors found no evidence that these newer devices increase risk when used within recommended parameters (Rossi et al., 2020).

This matters because deep TMS, which uses larger coils to reach deeper brain structures, has been approved for treating depression. Patients and clinicians need to know that the safety record extends to these newer approaches.

TMS in the Scanner: A New Frontier

Another major addition is guidance on using TMS inside MRI scanners and other neuroimaging environments. This combination, sometimes called interleaved TMS fMRI, allows researchers to stimulate one part of the brain while watching activity in the rest of the brain. It is a powerful technique, but it comes with its own risks. The magnetic fields from the MRI can interact with the TMS coil. The guidelines provide specific recommendations for safe operation, including the need for careful screening of subjects and equipment testing (Rossi et al., 2020).

When Two Brains Stimulation Techniques Meet

Researchers have also started combining TMS with transcranial electrical stimulation (tES), which uses weak electrical currents passed through electrodes on the scalp. The new guidelines address the safety of these combined protocols. The authors concluded that when both devices are used within their individual safety limits, the combination does not appear to increase risk (Rossi et al., 2020). This opens the door to more sophisticated experiments that might tease apart how different forms of brain stimulation interact.

Magnetic Seizure Therapy: A Deliberate Exception

One section of the guidelines deals with magnetic seizure therapy (MST), where TMS is used intentionally to induce a therapeutic seizure, similar to electroconvulsive therapy (ECT). This is a deliberate exception to the general safety rule. The authors note that MST appears to have fewer cognitive side effects than ECT, but they emphasize that it should only be performed by trained clinicians in controlled settings with appropriate monitoring (Rossi et al., 2020).

What the Guidelines Do Not Tell You

The new guidelines are comprehensive, but they are not a guarantee. They are based on the best available evidence, which is substantial but not infinite. The authors acknowledge several important gaps.

First, the safety data for novel stimulation parameters is limited. If a researcher invents a new pulse pattern or uses a coil in a way that has never been tried before, the old safety data may not apply. The guidelines recommend that any new protocol be tested first in animals or with careful neurophysiological monitoring in humans (Rossi et al., 2020).

Second, the guidelines do not address long term effects beyond a few years. Most studies follow subjects for weeks or months, not decades. The possibility of late emerging effects, though unlikely, cannot be ruled out.

Third, the guidelines are silent on the question of neuroenhancement. The authors include a brief note on ethics, stating that using TMS to improve cognitive function in healthy people raises ethical questions that go beyond safety (Rossi et al., 2020). They do not take a position, but they flag the issue for future debate.

The New Rules for Running a TMS Lab

The guidelines also include updated operational recommendations for anyone running a TMS study or clinic. These are not abstract. They are concrete.

Screening and Training

Every subject or patient must be screened for risk factors, including a history of seizures, epilepsy, or medications that lower the seizure threshold. The authors provide a standardized screening form. Operators must undergo specific training, including hands on practice and knowledge of emergency procedures. The guidelines specify minimum training requirements for different levels of TMS use (Rossi et al., 2020).

Monitoring During Stimulation

For standard protocols, the guidelines recommend that a trained operator be present at all times. For novel or high risk protocols, neurophysiological monitoring, such as EEG, may be necessary. The authors stress that the operator should be able to stop stimulation immediately if a seizure or other adverse event occurs (Rossi et al., 2020).

Device Maintenance and Manufacturer Responsibility

The guidelines place new emphasis on the responsibilities of device manufacturers. They must provide clear safety information, ensure that devices are properly maintained, and report adverse events. Researchers and clinicians should only use devices that meet international safety standards (Rossi et al., 2020).

What This Actually Means

The new guidelines from Rossi and his colleagues represent a shift from caution to confidence. The field has accumulated enough data to say that TMS is safer than many people assume. Here is what that means in practice.

• ▸If you are a researcher planning a TMS study, you can proceed with standard protocols without excessive fear of seizures. The risk is low enough that it should not be a primary concern, provided you follow the screening and monitoring guidelines.
• ▸If you are a patient considering TMS for depression, the safety record is reassuring. The treatment has been used in thousands of patients with few serious adverse events. The most common side effects are scalp discomfort and headache, not seizures.
• ▸If you are developing a new TMS protocol, you must still be cautious. The guidelines do not give blanket approval for untested approaches. Novel parameters require pilot testing and monitoring.
• ▸If you are combining TMS with other techniques, like fMRI or tES, the guidelines provide a clear path forward. The combination appears safe when each technique is used within its individual limits.
• ▸If you are worried about long term effects, the evidence is reassuring but incomplete. No signal of late emerging harm has appeared, but the field should continue to monitor subjects over longer periods.

The machine on your head is probably fine. The data now say so. But the guidelines are not a license for carelessness. They are a map for responsible use. And for a technology that can literally change how your brain fires, that is exactly what we need.