Key Takeaways
- TMS has a favorable safety record supported by decades of research and extensive clinical use.
- Headache and scalp discomfort are the most common side effects, and are generally mild and temporary.
- Seizures are the most serious recognized neurological complication, but are rare. One large study found approximately one seizure per 32,600 treatments.
- Human studies have generally not demonstrated persistent memory impairment or structural brain damage from conventional TMS.
- Animal studies examining brain tissue directly have produced reassuring findings, although certain experimental protocols can alter susceptibility to seizures.
- TMS safety depends on appropriate patient screening, treatment parameters, and clinical supervision.
How Safe Is TMS?
Transcranial magnetic stimulation (TMS) is a noninvasive medical treatment that uses brief magnetic pulses to stimulate specific regions of the brain. It is most commonly used to treat depression that has not responded adequately to antidepressant medications. Patients remain awake throughout treatment, no anesthesia is required, and most can return to their usual activities immediately afterward.
TMS first received FDA clearance for treating major depression in 2008. Since then, its use has expanded considerably, and researchers have accumulated extensive clinical experience evaluating its safety. The findings have generally been reassuring. Most adverse effects are relatively minor and resolve without lasting consequences.
However, no medical treatment is entirely without risk. The important questions are how frequently complications occur, how serious they are, and whether those risks can be reduced through careful treatment practices.
Fortunately, we have substantial clinical and experimental research addressing these questions.
What Are the Most Common Side Effects?
The most frequently reported adverse effects of TMS are headache and discomfort at the site where the magnetic coil rests against the scalp. Patients sometimes describe the sensation during treatment as tapping, tingling, or repetitive knocking against their head. The sensation is caused by the magnetic field causing contractions of the muscles of the scalp and eye, local to the device. Infrequently, there might be a nerve that is being triggered – perhaps generating jaw or tooth discomfort. These symptoms are generally temporary and often become less bothersome as patients become accustomed to treatment. In the case of a nerve being stimulated, usually the magnet is rotated slightly to get the magnetic flux field focused elsewhere.
In a randomized clinical trial reviewed by the FDA, 197 patients received either active TMS or a sham treatment. The investigators reported the following adverse events:
| Side Effect | Active TMS | Sham TMS |
|---|---|---|
| Headache | 32% | 23% |
| Scalp discomfort | 17.5% | 10% |
| Insomnia | 7.2% | 10% |
| Fatigue | 5.2% | 4% |
| Dizziness (vertigo) | 2.1% | 2% |
Source: FDA NeuroStar clinical data, submission K133408. These percentages represent the proportion of patients reporting each event, regardless of whether investigators considered the event directly related to treatment. [1]
What Is Sham TMS?
A sham treatment is the medical device equivalent of a placebo. In TMS research, patients assigned to the sham group undergo a procedure designed to resemble actual treatment without delivering the intended therapeutic magnetic stimulation to the brain. With a good sham, the participants should not know whether they are getting actual treatment or sham treatment.
Depending on the research equipment, a sham system may reproduce the clicking sounds made by the magnetic coil and sensations on the scalp similar to those produced during active treatment. As patients are generally unaware of which treatment they receive, researchers can distinguish effects associated with active stimulation from symptoms related to expectations, the treatment environment, or unrelated causes.
For example, headache was reported by 32% of patients receiving active TMS, but also by 23% receiving sham treatment. This suggests that while TMS may contribute to headaches, not every headache reported during treatment is necessarily caused by magnetic stimulation.
Interestingly, the differences between active and sham treatment for several reported adverse effects were quite small. This raises another intriguing question: is sham TMS always a genuine placebo?
Some sham systems reproduce the physical sensations of TMS by applying small electrical pulses to the scalp. Although these pulses do not deliver the intended magnetic stimulation to the brain, they may stimulate superficial nerves, particularly branches of the trigeminal nerve. This stimulation could potentially influence brain activity through pathways involved in emotional and autonomic regulation.
In fact, a 2025 study published in Brain Stimulation examined this very issue. Researchers found that electrical sham stimulation produced measurable changes in heart-brain coupling, a proposed marker of vagal and cortical activity. These changes were also associated with improvement in depression symptoms. The findings suggest that certain sham procedures may themselves produce biological effects, rather than functioning as completely inactive placebos.
This raises a fascinating methodological concern. If a supposedly inactive control treatment does, in fact, produce some antidepressant benefit, the difference between active TMS and sham treatment may underestimate the effects of magnetic stimulation. We may be comparing two forms of depression treatment: TMS vs. a weaker trigeminal stimulation. In picking a placebo that is not truly inactive, we then get data that underestimates the effectiveness of TMS.
The evidence is preliminary, and not all sham techniques involve electrical stimulation. Nevertheless, it both raises remarkable research questions and illustrates how difficult it can be to design a genuinely inactive control treatment for brain stimulation research. [2, 3]
Can TMS Cause Seizures?
Yes. Seizures are the most serious recognized neurological complication of TMS, although they are uncommon.
One of the largest investigations of seizure risk was published in Brain Stimulation in 2021. Researchers surveyed clinical TMS practices and collected information covering 586,656 treatment sessions involving 25,526 patients. Across those treatments, 18 seizures were reported.
This corresponds to approximately one seizure per 32,600 treatment sessions, or 0.003% per session.
The investigators also reported approximately 0.71 seizures per 1,000 patients, or about one per 1,400 patients in the surveyed population.
Although these figures are reassuring, they require interpretation. Seizure risk is not identical across all stimulation protocols or devices. The study found a higher reported seizure rate with H-coils than with the more conventional figure-eight coils. These differences do not necessarily establish that one system is inherently unsafe, but they demonstrate that the technology and stimulation parameters matter.
Certain medical circumstances may also increase seizure susceptibility, including a history of epilepsy, neurological abnormalities, alcohol withdrawal, and substantial sleep deprivation. Medications and changes in medication use should be reviewed, although available clinical evidence has not established that commonly prescribed psychiatric medications necessarily produce a substantial increase in TMS-related seizure risk.
Seizures have also occasionally occurred in individuals without identifiable risk factors. Consequently, risk can be reduced but cannot be completely eliminated. [4, 5]
Does TMS Cause Memory Loss or Brain Damage?
One understandable concern is whether repeatedly stimulating the brain might damage nerve cells or adversely affect memory and thinking.
Clinical studies of conventional therapeutic TMS have generally not demonstrated persistent cognitive impairment. Some patients actually report improvements in attention, concentration, or memory during treatment, although these changes may reflect recovery from depression rather than a direct cognitive benefit of stimulation.
There is also no convincing clinical evidence that conventional TMS, administered according to established safety guidelines, causes structural brain damage.
However, human research has limitations. Although MRI and cognitive testing can detect many abnormalities, they cannot necessarily identify subtle cellular injuries or microscopic tissue changes.
This is one reason animal research is valuable. [5]
What Have Animal Studies Shown About TMS Safety?
Animal studies allow researchers to investigate TMS safety in ways that are generally impossible in humans. After stimulation, investigators can examine brain tissue directly, looking for cellular injury, inflammatory changes, or abnormalities in brain metabolism.
In a 2003 study published in the Journal of Psychiatric Research, Liebetanz and colleagues administered repeated TMS to conscious rats over five consecutive days. The animals received 1,000 magnetic pulses daily at a frequency of 1 Hz. Researchers subsequently examined their brains using magnetic resonance spectroscopy and microscopic tissue analysis.
The investigators found no significant changes in several measured brain metabolites, including N-acetylaspartate, which is commonly used as a marker of neuronal integrity. They also found no evidence of increased microglial or astrocytic activation, changes that can indicate an inflammatory response or tissue injury.
These results were reassuring because they provided direct biological evidence that repeated TMS, under the conditions studied, did not produce detectable injury using those measures.
However, the findings do not establish that every TMS protocol is harmless. The study examined a relatively short course of low-frequency stimulation, rather than the higher-frequency or theta-burst protocols commonly used in modern depression treatment. [6]
Other animal research has explored whether repeated TMS changes the brain's susceptibility to seizures.
In a 1996 study, Jennum and Klitgaard administered repeated 50 Hz magnetic stimulation to rats. Although the stimulation itself did not produce overt tonic-clonic seizures, animals receiving chronic stimulation subsequently developed chemically induced seizures more readily than control animals. The researchers suggested that repeated high-frequency stimulation might increase seizure susceptibility under certain experimental conditions. [7]
Conversely, a 1999 study by Ebert and Ziemann found that a brief 20 Hz stimulation protocol increased the electrical threshold required to induce epileptic afterdischarges in rats, suggesting a potentially protective effect. [8]
These seemingly contradictory findings illustrate an important principle: the biological effects of TMS depend on stimulation frequency, intensity, duration, and the characteristics of the brain being stimulated.
Animal studies cannot precisely predict seizure risk or long-term neurological effects in humans. However, taken together with clinical research, they provide additional reassurance about conventional TMS while supporting continued caution with experimental or unusually intensive stimulation protocols.
What Other Risks Should Patients Know About?
Several additional risks deserve consideration, even though serious complications are uncommon.
- Hearing problems: TMS produces a loud clicking sound whenever the magnetic coil discharges. Repeated exposure without adequate hearing protection could potentially damage hearing. For this reason, properly fitted earplugs or other appropriate hearing protection should be available during treatment.
- Mania or hypomania: Occasionally, patients develop elevated mood, increased energy, reduced need for sleep, or unusual agitation during a course of treatment. This possibility is particularly relevant for patients with bipolar disorder, although mood switching has also been reported in people initially diagnosed with unipolar depression. Bipolar disorder is not a contraindication to getting TMS but one should exercise precautions.
- Fainting: Rarely, some patients experience vasovagal episodes, particularly during their first few treatments. These episodes may involve dizziness, sweating, nausea, or temporary loss of consciousness. They are usually self-limited but need to be distinguished from seizures or other medical complications.
- Medical implants: Magnetic stimulation can interact with certain implanted medical devices and conductive materials near the head. Cochlear implants, implanted electronic stimulators, and some other devices may be incompatible with TMS. Ordinary dental fillings and many other common implants are generally not a problem, but careful screening is necessary. [5]
What Does FDA Clearance Mean?
TMS first received FDA clearance for major depressive disorder in adults in 2008. FDA clearance means that a device has met the regulatory requirements for marketing for specific medical indications. It does not mean the treatment is completely risk-free or that every TMS device is cleared for every psychiatric condition.
Different manufacturers and devices have received different clearances over time. NeuroStar, the system used at Diamond Edge TMS, has received additional clearances for adjunctive treatment of obsessive-compulsive disorder in adults, reduction of anxiety symptoms in patients with major depression, and adjunctive treatment of major depressive disorder in adolescents ages 15 through 21.
These indications are specific. For example, clearance for reducing anxiety symptoms associated with major depression does not automatically mean that TMS is cleared for treating all primary anxiety disorders.
It is also important to distinguish established treatment protocols from newer approaches. Some techniques, including accelerated treatment schedules, multiple sessions per day, or stimulation of alternative brain regions, may differ from the protocols originally evaluated by the FDA. These variations are sometimes described as off-label treatments, meaning that a physician is using an FDA-cleared device in a manner that falls outside its specific cleared indications or treatment parameters. Such approaches may be supported by clinical research and experience, but they may not have undergone the same level of FDA review or accumulated the same extensive safety data as established protocols. Importantly, off-label does not necessarily mean experimental, ineffective, or unsafe.
The Bottom Line: How Safe Is TMS?
After nearly two decades of clinical use in the United States, TMS has developed a favorable safety record. The most commonly reported adverse effects are headache and scalp discomfort, which are generally temporary. Serious neurological complications, particularly seizures, are rare.
Clinical research has not demonstrated persistent cognitive impairment or structural brain injury from conventional therapeutic TMS. Animal studies examining brain tissue directly provide additional reassurance, while also demonstrating that different stimulation protocols can have different physiological effects.
TMS remains a medical procedure rather than a risk-free intervention. Its safety depends on appropriate patient selection, established stimulation parameters, careful screening for neurological risk factors and implanted devices, and clinical staff trained to recognize and respond to complications.
For most appropriately selected patients receiving conventional TMS, the available scientific evidence supports a relatively low risk of serious adverse effects.
About Diamond Edge TMS
Diamond Edge TMS in Vancouver, Washington, provides NeuroStar TMS treatment under the supervision of Dr. Jerald Block, a board-certified psychiatrist with more than 25 years of clinical experience.
For more information, visit Diamond Edge TMS or call (360) 838-3654.
Scientific References
Human clinical studies and safety guidelines
1. U.S. Food and Drug Administration. NeuroStar TMS Therapy System, K133408. FDA 510(k) documentation, including randomized trial adverse-event data and sham-treatment comparisons.
2. Arns M, Williams NR, Downar J, Dojnov A, Coetzee J, Goya-Maldonado R. (2025). Trigeminal nerve stimulation as an active control condition in TMS clinical trials: Evidence from heart-brain coupling and clinical outcomes. Brain Stimulation, 18(5), 1403–1406.
3. Mennemeier M, et al. (2010). Sham transcranial magnetic stimulation using electrical stimulation of the scalp. Brain Stimulation.
4. Taylor JJ, Newberger NG, Stern AP, et al. (2021). Seizure risk with repetitive TMS: Survey results from over a half-million treatment sessions. Brain Stimulation, 14(4), 965–973.
5. Rossi S, Antal A, Bestmann S, et al. (2021). Safety and recommendations for TMS use in healthy subjects and patient populations, with updates on training, ethical and regulatory issues: Expert Guidelines. Clinical Neurophysiology, 132(1), 269–306.
Animal studies
6. Liebetanz D, Fauser S, Michaelis T, et al. (2003). Safety aspects of chronic low-frequency transcranial magnetic stimulation based on localized proton magnetic resonance spectroscopy and histology of the rat brain. Journal of Psychiatric Research, 37(4), 277–286.
7. Jennum P, Klitgaard H. (1996). Repetitive transcranial magnetic stimulations of the rat: Effect of acute and chronic stimulations on pentylenetetrazole-induced clonic seizures. Epilepsy Research, 23(2), 115–122.
8. Ebert U, Ziemann U. (1999). Altered seizure susceptibility after high-frequency transcranial magnetic stimulation in rats. Neuroscience Letters, 273(3), 155–158.
