Deep Brain Stimulation (DBS) Side Effects Explained

Deep brain stimulation carries a wide spectrum of possible side effects, from surgical complications like infection and bleeding to stimulation-driven problems with speech, mood, balance, and cognition. Most are manageable through programming adjustments or medication changes, but some can be serious or even life-threatening. The picture is complicated by the fact that different brain targets, electrode placements, and stimulation settings produce different risk profiles, so two people with the same device can have very different experiences.

Why Stimulation Causes Unintended Effects

The electrodes used in DBS deliver electrical pulses to a small region of brain tissue, but the current does not stay neatly inside the intended target. Computational modeling shows that at typical clinical settings, the electrical field activates nerve fibers across a volume that extends beyond the borders of the target nucleus itself, with the shape of that activation zone influenced by the tissue surrounding the electrode tip.

When this spread reaches nearby structures, side effects follow. The internal capsule, a dense highway of nerve fibers running close to common DBS targets, is a frequent culprit. Stimulation that drifts into portions of the internal capsule can activate motor pathways and trigger involuntary muscle contractions, tingling, or speech difficulties.

This is the core trade-off in DBS programming: turning the stimulation up improves symptoms but widens the electrical field, increasing the chance it will hit something it shouldn’t. Turning it down reduces side effects but may leave symptoms undertreated. Most of the stimulation-related side effects described below trace back to this basic geometry problem.

Surgical and Hardware Complications

Before any stimulation-related side effects enter the picture, there are the risks of the surgery itself. A large single-center study following 426 patients over 21 years found that about 6% required revision surgery for complications. Infection was the most common issue, accounting for roughly 44% of all complications requiring reoperation, with most infections occurring along the extension wires under the skin rather than inside the brain itself. Intracranial bleeding occurred in several patients, ranging from small hemorrhages that resolved on their own to major bleeds requiring surgical evacuation.¹

Hardware problems develop over the longer term. A decade-long case series from a national neurosurgery center found lead fractures in about 5% of patients. Most fractures happened below the collarbone, and nearly all patients with a fractured lead reported a history of trauma or vigorous physical activity. A small number of cases involved “Twiddler’s syndrome,” where a patient unconsciously rotates or fidgets with the implanted pulse generator under the skin, eventually twisting and breaking the lead wire.² When a lead fractures, stimulation either cuts out abruptly or becomes erratic, and a second surgery is needed to replace the damaged component.

Speech and Voice Changes

Difficulty with speech is one of the most commonly reported stimulation-related side effects, particularly for people receiving DBS in the subthalamic nucleus for Parkinson’s disease. The problem is not simply that speech gets quieter or more slurred; research has identified distinct types of stimulation-induced speech difficulty that map onto different brain networks. One pattern involves a spastic quality linked to activation of the motor cortex and supplementary motor area, suggesting the current is disrupting the nerve fibers that control the muscles of speech. A different pattern involves a strained voice quality connected to more frontal brain regions, pointing to disruption of the motor planning of speech rather than the muscles themselves.³

Stimulation frequency plays a role. Studies comparing different frequency settings have found that the higher frequencies typically used to control tremor and rigidity tend to worsen articulation, voice quality, and the overall grade of speech difficulty.⁴ This puts clinicians in a bind: the settings that best control motor symptoms are often the same ones that make speech worse. For some patients, finding a workable compromise takes months of reprogramming.

Cognitive Effects and Verbal Fluency

Verbal fluency decline is one of the most reliably documented cognitive side effects of subthalamic nucleus DBS.⁵ In practical terms, this means people find it harder to generate words on demand, like naming as many animals as possible in one minute. The effect is most pronounced in the semantic category, where you draw on stored knowledge rather than searching by letter.

This decline is not random. Age at the time of surgery and how long someone has had Parkinson’s disease both influence how much verbal fluency drops.⁶ Broader cognitive outcomes after DBS also track with these factors. Reviews of the evidence identify age and preoperative cognitive status as the most robust predictors of post-surgical cognitive decline, though the field cannot yet offer precise risk estimates for individual patients.⁷ Other risk factors linked to worse cognitive outcomes include preexisting executive dysfunction, higher preoperative doses of levodopa, and more severe balance and posture problems before surgery.⁸

Recent work has added an interesting wrinkle: the relationship between electrode placement and cognition may flip depending on the patient’s age. In one study, DBS sites with stronger connectivity to a specific part of the hippocampus were associated with better cognitive outcomes in older patients but worse outcomes in younger ones.⁹ This suggests that the “ideal” electrode placement for preserving cognition may not be the same for every patient, which complicates surgical planning.

Apathy, Mood Changes, and Behavioral Shifts

Apathy is one of the more insidious side effects because it creeps in gradually and can be hard to distinguish from the disease itself. A meta-analysis pooling results across multiple studies found that apathy scores were significantly higher after subthalamic DBS than before surgery, and also higher compared to patients managed with medication alone. The effect persisted even after accounting for reductions in dopamine-boosting drugs, suggesting it is at least partly a direct consequence of the stimulation rather than just a side effect of lowering medication doses.¹⁰

Longitudinal tracking confirms the pattern: apathy tends to increase steadily over the months following surgery, with significant individual variation in how quickly and how severely it develops.¹¹ For some patients, the gain in motor function is offset by a new flatness of motivation that affects relationships, hobbies, and daily initiative.

Impulse control disorders present the opposite problem. These include compulsive gambling, binge eating, hypersexuality, and excessive spending. The relationship between DBS and these behaviors is complicated. Some patients develop new impulse control problems after surgery, while others who had pre-existing compulsive behaviors on dopamine medications see those behaviors persist or worsen despite medication reduction. A review of the literature found that over half of reported cases of impulse control disorders in DBS patients had poor outcomes regardless of the treatment approach.¹²

Motor Side Effects and Balance Problems

It might seem paradoxical that a treatment for movement disorders can cause movement disorders, but it happens. Subthalamic nucleus stimulation has been associated with various involuntary movements including dyskinesias, involuntary eyelid closure, and difficulty opening the eyes. Stimulation of the globus pallidus, the other common target, has been linked to worsening of slowness and freezing of gait.¹³

Balance and walking are particular weak spots. While DBS reliably improves limb tremor and rigidity, its effects on gait and postural stability are much less consistent and can actually make freezing of gait and imbalance worse.¹⁴ This is a significant issue because falls are one of the biggest sources of injury and hospitalization in people with Parkinson’s disease, and a treatment that improves hand tremor at the cost of more frequent falls may not be a net win.

How the Brain Target Changes the Side Effect Profile

The two most common targets for DBS in Parkinson’s disease, the subthalamic nucleus and the globus pallidus internus, produce broadly similar improvements in motor symptoms, but their side effect profiles diverge in meaningful ways. Based on the highest quality evidence available, subthalamic stimulation is associated with greater cognitive decline in specific domains and a higher or equal risk of mood disturbance compared to pallidal stimulation.¹⁵

The tradeoff extends beyond side effects. Subthalamic DBS allows for greater reduction in dopamine medications after surgery, which matters because those medications carry their own side effects. Subthalamic stimulation also draws less power, meaning fewer battery replacements over the device’s lifetime. Pallidal stimulation, on the other hand, offers more straightforward programming and may be a better choice when the priority is suppressing medication-induced involuntary movements.¹⁶ In practice, the choice of target often comes down to which side effects a particular patient is most vulnerable to. Someone with preexisting cognitive vulnerability might be better served by pallidal stimulation, while someone primarily struggling with medication burden might lean toward the subthalamic target.

Autonomic and Non-Motor Effects

DBS does not only affect movement and thinking. It also influences the autonomic nervous system, the body’s autopilot for functions like digestion, blood pressure, bladder control, and temperature regulation. The overall picture is mixed. Most research on subthalamic stimulation reports favorable effects on gastrointestinal function and bladder control, but some patients experience new or worsening autonomic symptoms after surgery. The evidence is more conflicting for cardiovascular function, breathing, temperature regulation, and sexual function.¹⁷

A broader review of non-motor symptoms found that DBS generally helps with sensory complaints, sleep problems, sweating, and urinary symptoms.¹⁸ These improvements rarely get headline attention compared to the motor benefits, but for someone whose most bothersome symptom is urinary urgency or drenching night sweats, they can be as meaningful as tremor control.

What Happens When Stimulation Stops Suddenly

One side effect that catches many patients and even some clinicians off guard is what happens when stimulation is abruptly interrupted. In rare cases, sudden loss of subthalamic stimulation can trigger a life-threatening akinetic crisis, sometimes called malignant DBS withdrawal syndrome. The symptoms resemble neuroleptic malignant syndrome: extreme rigidity, high fever, impaired consciousness, and autonomic instability. Case reports describe patients enduring prolonged and severe crises after abrupt loss of stimulation, whether from a dead battery, a broken lead, or an accidental shutoff.¹⁹

This risk underscores why patients are advised to carry a spare programmer and to seek emergency care quickly if their device stops working. It also means that battery replacement surgery needs to be scheduled before the device runs down completely, not after symptoms start rebounding.

Newer Technologies Aimed at Reducing Side Effects

Much of the field’s recent energy has gone into making stimulation more precise. Directional leads, which can steer the electrical field toward or away from specific tissue, represent the most widely adopted advance. Rather than sending current out in all directions equally, these leads can focus the field in one direction, potentially keeping it inside the target and away from the internal capsule or other structures that cause side effects. Systematic reviews suggest that directional stimulation produces motor improvements comparable to conventional omnidirectional stimulation, with consistent gains in the therapeutic window, meaning clinicians have more room to increase stimulation before side effects appear.²⁰

Adaptive or “closed-loop” DBS takes a different approach. Instead of delivering constant stimulation around the clock, adaptive systems read brain signals in real time and adjust stimulation moment to moment based on what the brain is actually doing. The rationale is that continuous stimulation is wasteful and potentially harmful: a brain at rest does not need the same voltage as one trying to initiate a movement. By matching stimulation to demand, adaptive DBS aims to reduce both side effects and battery drain.²¹ Early clinical data have been encouraging, but adaptive DBS is still in the relatively early stages of commercial deployment, and long-term side effect comparisons with conventional systems are limited.

The Psychological Adjustment That Nobody Warns You About

Even when DBS works exactly as intended, the psychological aftermath can be surprisingly difficult. Clinicians and researchers have documented a phenomenon sometimes called the “burden of normality,” where people whose severe symptoms are dramatically reduced find themselves struggling with an identity crisis. Years of disability have shaped their relationships, daily routines, career trajectory, and self-concept. When the disease is suddenly better controlled, the person is left facing questions they may not have anticipated: Who am I without this illness? What do I do with the capabilities I now have? Why don’t I feel happier?

A detailed case study of a patient treated with DBS for severe obsessive-compulsive disorder illustrates the pattern. Symptom remission opened up new possibilities, but it also brought intense distress related to the changed sense of self. The shift was not just positive; it was destabilizing.²² This kind of adjustment difficulty does not show up on a standard side-effect checklist, but it is real and can significantly affect quality of life in the months and years after surgery.

How Patients Weigh Benefits Against Side Effects

Interestingly, when researchers have directly asked patients how they think about the tradeoffs, the pattern is consistent: the mode of treatment matters more to them than the risk of side effects. In a large study that presented patients with various hypothetical treatment scenarios, the option of neurosurgery was rated the least desirable treatment method overall, while oral medication was rated most desirable, regardless of the outcomes attached. The impact of the treatment on motor symptoms like posture, balance, and slowness ranked well above the occurrence of side effects in determining how attractive patients found a treatment option. Only about a third of patients said side effects were very influential in their treatment decision, compared to two-thirds who said the same about benefits.²³

This finding has a practical implication for people considering DBS: the side effects are real and varied, but most patients who actually undergo the procedure report that the motor benefits were worth the tradeoffs. The patients most likely to regret the decision tend to be those who had unrealistic expectations about what DBS would fix, particularly regarding non-motor symptoms like speech, balance, and cognitive sharpness that the device does not reliably improve and may worsen. An honest pre-surgical conversation about what DBS cannot do matters at least as much as discussing what can go wrong.