Transcranial magnetic stimulation has become an increasingly common treatment for people living with depression that does not respond to medication, yet new academic work is raising questions about how confidently clinicians can choose between its two most widely used forms.
Repetitive transcranial magnetic stimulation, known as rTMS, and deep transcranial magnetic stimulation, or dTMS, are now offered by a growing number of specialist centres. Both techniques are generally regarded as safe and more effective than placebo. However, despite their rapid clinical uptake, there is still little high quality evidence showing whether one is more effective than the other, or which patients are most likely to benefit from each approach.
The issue has been examined by Walter Paganin, a clinician and neuroscience researcher specialising in treatment resistant depression. In a systematic review published in the Journal of Neural Transmission, Paganin assessed the available evidence comparing rTMS and dTMS. The review identified only three studies that directly compared the two techniques, all of which were limited by methodological weaknesses, making firm conclusions difficult.
While the review focused on clinical efficacy and safety, it also highlighted a broader problem. The widespread use of both technologies has outpaced the strength of the comparative evidence supporting them. Paganin argues that this gap has important implications beyond clinical outcomes alone.
In a subsequent opinion paper published in Frontiers in Psychiatry, Paganin expands the discussion to include regulatory, economic, and ethical considerations. The paper argues that treating rTMS and dTMS as largely interchangeable interventions is problematic when robust head to head data are lacking, particularly in relation to cost effectiveness and equitable access.
Although both techniques rely on magnetic stimulation, they differ substantially in how they interact with the brain. rTMS typically uses a figure of eight coil, allowing relatively focal stimulation of surface brain regions, most commonly the dorsolateral prefrontal cortex. This precision allows flexibility in treatment protocols but also introduces variability that complicates comparisons across studies.
dTMS, by contrast, uses a larger H coil designed to stimulate deeper and broader brain areas. This increased depth comes at the expense of focal precision, meaning the two approaches represent distinct neuromodulation strategies rather than minor technical variations of the same treatment.
One of the most significant gaps identified in Paganin’s work concerns cost. No published study has directly compared the cost effectiveness of rTMS and dTMS. This absence of data leaves healthcare systems and clinics investing in expensive technologies without clear evidence that higher costs translate into superior outcomes. In general terms, rTMS systems tend to involve lower equipment and maintenance costs and simpler training requirements, whereas dTMS systems are more expensive to purchase and operate.
The lack of economic evidence also raises ethical concerns. Paganin questions whether it is justifiable to offer higher cost treatments without strong evidence of added benefit, particularly in healthcare systems with limited resources. In such settings, decisions about which technology to adopt can become political and ethical choices as much as clinical ones.
The opinion paper also discusses emerging interest in personalised approaches to neuromodulation. Researchers are exploring whether biological markers, such as inflammatory profiles or patterns of brain connectivity, could one day help guide decisions about whether superficial or deeper stimulation is more appropriate for individual patients. At present, however, these approaches remain speculative and cannot substitute for well designed comparative trials.
According to Paganin, the central issue is not a lack of technology but a lack of comparative evidence. He argues that independent, multicentre studies with adequate follow up and integrated economic analyses are needed to inform clinical practice. Until such data are available, decisions between rTMS and dTMS will continue to reflect not only scientific uncertainty, but also the priorities and constraints of healthcare systems.