TMS, or transcranial magnetic stimulation, is a non-invasive brain stimulation therapy used to treat major depressive disorder. It works by delivering magnetic pulses to the front of the brain through a device placed against the scalp, no surgery or anesthesia required. The FDA classifies it as a treatment for adults who haven’t improved with at least one antidepressant medication, making it a next-step option when pills alone aren’t enough.
How TMS Works on the Brain
During a TMS session, an electromagnetic coil placed against your head generates rapid magnetic pulses that pass through the skull and create small electrical currents in brain tissue. These currents are strongest just beneath the surface of the skull where the coil sits, and they’re targeted at a region called the left dorsolateral prefrontal cortex, an area involved in mood regulation that tends to be underactive in people with depression.
The exact mechanism isn’t fully understood, but the leading theory is that repeated stimulation changes the way neural structures process emotion. Over the course of treatment, the pulses appear to promote the growth of new connections between brain cells and increase the volume of cortical tissue in areas linked to depression. In short, TMS seems to help the brain rewire itself, restoring activity in circuits that depression has quieted down.
What a Treatment Course Looks Like
A standard TMS course involves daily sessions, five days a week, for four to six weeks. Most people complete around 36 sessions total, though individual treatment plans can range from as few as 6 to over 50 depending on how someone responds. Each session with a standard protocol lasts roughly 20 to 40 minutes, depending on the type of device used.
Before your first treatment session, a clinician will calibrate the machine to your brain. This is done through a process called motor threshold mapping: the coil is placed over the part of the brain that controls hand movement, and the intensity is gradually adjusted until it causes a small, visible twitch in your thumb or fingers. This threshold tells the clinician exactly how much power is needed to activate your neurons, and the treatment intensity is then set as a percentage of that number (typically 120% of your resting motor threshold). The whole calibration process is painless and takes just a few minutes.
During the session itself, you sit in a chair while the coil is held against your head. You’ll hear clicking sounds and feel a tapping sensation on your scalp. There’s no sedation, no recovery time. Most people drive themselves to and from appointments and return to their normal routine immediately after.
How Effective TMS Is
TMS doesn’t work for everyone, but it helps a meaningful percentage of people who haven’t responded to medication. In a real-world study of patients who had failed four or more antidepressant trials, 38.1% showed a significant improvement in symptoms by the end of their TMS course, and 20.2% achieved full remission. For comparison, a similar group treated with medication alone had a 23.3% response rate and a 12.4% remission rate. These numbers may sound modest, but they represent gains in a population that, by definition, hadn’t responded to previous treatments.
The benefits also tend to last. In a one-year follow-up study of patients who responded to acute TMS treatment, 62.5% maintained their improvement throughout the entire follow-up period. Some people do experience a return of symptoms over time and may benefit from periodic “maintenance” sessions, but the majority of responders retain a meaningful benefit well after treatment ends.
Side Effects and Safety
The most common side effect is discomfort or mild pain at the stimulation site during treatment. Some people get headaches, particularly in the first week or two, which typically diminish as sessions continue. Scalp tenderness is also common early on.
The most serious potential risk is a seizure, but this is extremely rare. A large review of over 318,000 TMS sessions found just 24 seizures, putting the risk at roughly 1 in 60,000 sessions for people without additional risk factors. Certain things can increase that small risk, including heavy alcohol use, sleep deprivation, and a history of brain injury. Your provider will screen for these before starting treatment.
One notable advantage of TMS over other brain stimulation therapies: it doesn’t cause the cognitive side effects associated with electroconvulsive therapy (ECT). ECT, which requires general anesthesia and induces a seizure, is known to cause memory problems. TMS has actually been shown to mildly improve working memory and retrograde memory in some patients.
Standard TMS vs. Deep TMS
There are two main types of TMS devices in clinical use. Standard repetitive TMS (rTMS) uses a figure-8 shaped coil that delivers focused stimulation to about 1 to 1.5 centimeters below the skull surface. Deep TMS (dTMS) uses a different coil design called an H-coil, which generates a broader magnetic field that penetrates 3 to 4 centimeters deep, reaching structures further inside the brain’s mood-regulation circuitry.
Deep TMS sessions tend to be shorter and require fewer pulses, and the positioning of the coil is less sensitive to small placement errors. Standard rTMS offers more precise targeting of a specific brain area. Both are FDA-cleared for major depressive disorder, and there’s no definitive evidence yet that one produces consistently better outcomes than the other for depression.
Insurance Coverage and Eligibility
Professional medical societies recommend TMS for adults with moderate to severe depression who have failed one or two antidepressant medications. The FDA’s clearance uses a similar threshold: at least one failed medication trial at an adequate dose and duration.
Insurance coverage, however, varies widely. Some insurers follow the clinical guidelines closely, while others set a much higher bar. Optum, for example, requires patients to have failed four antidepressant trials plus a course of psychotherapy before approving coverage. Cigna requires two failed antidepressant trials and psychotherapy. Some plans also require that you’ve tried augmentation strategies, like adding a second type of medication to your antidepressant, before they’ll cover TMS. Different companies use different rating scales and severity cutoffs to determine eligibility, so the specifics depend entirely on your plan.
If you’re considering TMS, your provider’s office will typically handle the prior authorization process and can tell you early on whether your insurance is likely to cover it based on your treatment history. Out-of-pocket costs without insurance can run into the thousands of dollars for a full course, making the coverage question a practical one for most people.