Neurostimulation (tDCS / TMS)

Two procedures, one name

In TMS, a magnetic coil is placed on the head. It generates short, strong magnetic fields that induce a current in the underlying cerebral cortex. When the pulses are repeated in series, this is called rTMS. Depending on the frequency, the region is either stimulated or dampened. Treatment takes place in a clinic or practice; according to the guideline, 5 sessions per week of 20 to 30 minutes each over 3 to 6 weeks are typical.

In tDCS, two electrodes are stuck to the scalp, and a weak direct current in the range of a few milliamperes flows between them. It does not trigger nerve impulses, but makes nerve cells under the anode somewhat more excitable and those under the cathode somewhat more sluggish. The devices are small, inexpensive and available for home use. That is exactly why tDCS is the procedure circulating in the biohacking scene.

How it is supposed to work

In depression, activity in the left front part of the frontal lobe, the dorsolateral prefrontal cortex, is often altered. Both procedures usually target this region. Repeated stimulation is supposed to trigger learning processes at the synapses there, similar to training. With rTMS, the direct activation of the cerebral cortex can be measured well in humans, for example as a muscle twitch when the coil is placed over the motor area.

For tDCS the picture is less clear. The current fields spread widely across the frontal lobe, and the effect depends strongly on what the brain is doing at the time. This partly explains why studies with a similar design deliver such different results.

How to recognize reputable offers

rTMS belongs in a psychiatric clinic or practice with a diagnosis, informed consent and a defined protocol. The guideline recommends that a specialized center select the site and type of stimulation. With tDCS home devices, skepticism is warranted when manufacturers promise more intelligence, focus or learning speed. There are no reliable data for this in healthy people. It is also striking how much the sham treatment improved in depression studies, an indication of how much expectation matters.

What the studies show

Brunoni 2017 — rTMS in depression

Network meta-analysis of 81 randomized trials with 4,233 patients, including only studies with at least 10 sessions. High-frequency, low-frequency, bilateral and theta-burst stimulation were more effective than sham. Newer variants such as accelerated or deep TMS did not perform better than sham in this analysis.

DepressionDC 2023 — tDCS in addition to antidepressants

Triple-blind trial at 8 German clinics with 160 patients who remained depressed despite an antidepressant. For 6 weeks, 30 minutes of stimulation at 2 milliamperes or sham stimulation. The primary endpoint, improvement on the depression scale, was missed; the difference was 0.3 points. Mild side effects occurred more often under active stimulation, in 60 versus 43 percent.

Horvath 2015 — tDCS and cognition in healthy people

The largest quantitative analysis up to that point on single-session tDCS in healthy adults. Across 59 analyses of working memory, language, executive functions and other tests, not a single significant effect was found, regardless of how strict the inclusion criteria were.

Where the data stop

For the typical biohacking use, that is, tDCS for focus, learning or productivity in healthy people, there is no reliable evidence. The large analysis of single sessions found nothing, and studies on repeated use in healthy people are small and inconsistent. Even in depression, the tDCS effect remains small, remission does not increase significantly, and larger studies show smaller effects. The German guideline therefore makes no recommendation for tDCS.

For rTMS it is unclear how long the effect lasts, and the quality of evidence ranges from very low to moderate depending on the procedure. For healthy people who want to boost their performance, rTMS has not been studied either.

Status, approval and legal

In Germany, rTMS is a medical procedure for the treatment of depression and, according to the guideline, has so far been offered at only a few clinics; reimbursement was changed in 2021. In the US, TMS is approved for adults with depression after unsuccessful antidepressants. In Germany, tDCS is approved as a medical device on safety grounds; there is no approval based on proof of efficacy in depression, and statutory health insurers do not pay. Since June 22, 2023, common EU-wide safety specifications have applied to home devices for brain stimulation without an intended medical purpose. Reputable providers treat after a diagnosis, with a fixed protocol and under medical supervision.

Safety

With rTMS, unusual sensations on the scalp and temporary headaches are the most common; discomfort or headache occurred in studies in 20 percent versus 10 percent under sham. Very rarely, an epileptic seizure can be triggered, which is why people are asked beforehand about epilepsy, metal in the head and implants. With tDCS, tingling, itching and redness under the electrodes are typical. The guideline mentions skin burns with incorrect use and the risk of hypomanic or manic symptoms. Anyone with bipolar disorder, epilepsy, implants in the head or a pacemaker should not use home devices without consulting a physician.

Sources

• German National Care Guideline (NVL) Unipolar Depression, version 3.2, long version
• Brunoni et al., JAMA Psychiatry 2017 (rTMS, network meta-analysis)
• Burkhardt et al., Lancet 2023 (DepressionDC)
• Razza et al., Br J Psychiatry 2026 (tDCS, IPD meta-analysis)
• Horvath et al., Brain Stimul 2015 (tDCS and cognition in healthy people)
• Bikson et al., Brain Stimul 2016 (safety of tDCS)
• Perera et al., Brain Stimul 2016 (consensus on TMS in depression)
• Implementing Regulation (EU) 2022/2346 (products without an intended medical purpose)