The full potential of VNS therapy is not fully known. Because of the range of brain and body functions controlled by the vagus nerve, it is thought that vagus nerve stimulation could be used as a treatment method for a variety of medical conditions. To date, the Food and Drug Administration (FDA) has only approved the use of vagus nerve stimulation to treat epilepsy and some cases of severe depression.

Epilepsy is a neurological disorder that involves a tendency to experience recurrent seizure activity in the brain. This can be the result of an underlying medical condition or injury, which makes a person susceptible to recurring seizures. In many cases, the cause is unknown.

VNS therapy may be recommended to reduce seizures when medication or conventional brain surgery is not effective. It is usually considered as an option for patients who have tried two or more medications and who are unsuitable for or unwilling to undergo brain surgery. Vagus nerve stimulation is a form of add-on therapy, which means that it must be used in conjunction with other forms of seizure control, such as seizure medications or brain surgery. Research indicates that this treatment, used with seizure medication, is able to reduce seizures by up to 40 percent in some people. However, in others, vagus nerve stimulation does not work as well, with some patients reporting no change or a worsening of their seizures. It is unclear why vagus nerve stimulation works better for some patients than for others.   

Vagus nerve stimulation is also used to treat severe chronic depression, which is characterized by an altered, usually profoundly sad mood and a loss of interest or pleasure in activities that were once enjoyable. Vagus nerve stimulation was first explored as an option for treating depression when it was observed that some people with epilepsy who underwent the treatment experienced a general improvement in mood, even if the device had no effect on the patient’s epilepsy.

Vagus nerve stimulation is generally considered as a treatment option for severe depression that has not responded to at least four other treatment methods. However, despite FDA approval, the evidence is inconsistent in demonstrating that vagus nerve stimulation is an effective treatment method for severe chronic depression.

There is also some evidence to suggest that vagus nerve stimulation could be used to treat intractable migraines, fibromyalgia, chronic pain and Alzheimer's disease although its use for these purposes has yet to complete clinical trials and is not approved by the FDA.