Does TENS Machine Have Side Effects: What Studies Say?

TENS is widely used by physiotherapists and patients at home. What side effects have been described? Is it dangerous to use?

Can it increase pain instead of relieving it?

I draw on my experience as a physiotherapist and extensive research into studies using and evaluating TENS to answer these questions.

Good reading 🙂!

What is Transcutaneous Electrical Nerve Stimulation (TENS) and when is it used?

First, let’s clarify the type of electrotherapy we are referring to here and why.

Physiotherapy/Electrotherapy/TENS: What are the differences?

Physiotherapy is synonymous with physical therapy in most countries around the world.

In some countries like France, physiotherapy refers to a range of passive techniques used primarily for pain relief, such as hot and cold applications, massages, electrotherapy, etc.

Electrotherapy refers to all techniques that utilize electricity to alleviate pain or treat other health issues.

Here are the main devices and machines used for electrotherapy:

• TENS (Transcutaneous Electrical Nerve Stimulation)
• Endorphinic currents
• Electrical muscle stimulation, excitomotor currents
• Iontophoresis
• Pulsed electromagnetic field
• Repetitive magnetic stimulation

This article focuses solely on TENS.

TENS stands for Transcutaneous Electrical Nerve Stimulation. In simple terms, TENS is a device that applies electrical currents to the skin’s surface using electrodes to relieve pain in the targeted area. It is not intended for muscle stimulation or strengthening.

There are different types of electrotherapy devices. When it comes to pain relief, the most commonly used type of electrotherapy is TENS (Transcutaneous Electrical Nerve Stimulation).

How does TENS provide relief (mechanism of action)?

In the 1980s, several studies examined what happens in the body when TENS is applied.

Here’s what occurs:

1. The electrical current stimulates the peripheral nerves that pass through the area where TENS is applied.
2. These nerves trigger the secretion of chemical substances and nerve impulses that provide information to the brain’s pain-controlling neurons.
3. The electrical and chemical information is transmitted to neurons in the brain, instructing the neurons sending painful messages to become less active.

The question to consider is: Do these nerve impulses send a strong enough message to the brain to truly reduce pain? And is the effect long-lasting?

To find out, TENS has been tested on a large number of people. The progress of pain in these individuals was compared to the pain progression in those who received no pain treatment or other treatments (medications, other physiotherapy techniques, massage, etc.).

Now, let’s examine the results of these types of studies.

What do the studies say about the effectiveness of TENS machine?

The initial studies evaluating the effectiveness of TENS date back to the 1970s. There are over 1500 scientific publications on the subject of TENS.

The Cochrane reviews

In order to obtain a broad and reliable overview of the effectiveness of TENS for various types of pain, I searched for all publications from the Cochrane Collaboration. This non-profit international organization conducts rigorous literature reviews, which are considered among the best in the world.

Here is a list of different types of pain for which the effectiveness of TENS has been evaluated by a Cochrane review:

Pathology/Pain Type	Efficacy
Neuropathic pain in adults	?
Phantom limb pain	?
Fibromyalgia in adults	?
Chronic low back pain	?
Acute pain	+
Labor pain	+
Chronic neck pain	?
Cancer-related pain in adults	?
Knee osteoarthritis	?
Rheumatoid arthritis (hand)	?
Sickle cell disease	?
Shoulder pain after stroke	?
Dysmenorrhea (menstrual pain)	+
Frozen shoulder	?
Chronic pain in multiple sclerosis	+

These Cochrane reviews not only examine the effectiveness of TENS in relieving pain but also its impact on other parameters such as return to work, resumption of physical activity, and improved quality of life.

While TENS may be effective for some people in relieving pain, its effectiveness in these other areas is less established.

What can we conclude from this table?

1. It is unclear whether TENS is effective for chronic pain.
2. While some individuals may respond well to TENS, there is no clear overall trend.
3. However, it appears to be more effective for acute, temporary pain (such as acute low back pain).

Here are the conclusions from a Cochrane publication that summarizes all Cochrane reviews on the effectiveness of TENS for chronic pain:

Therefore, we were unable to conclude with certainty whether TENS is harmful or beneficial in relieving pain, reducing disability, improving health-related quality of life, limiting the use of pain medication, or producing a global impression of change in individuals with chronic pain.

Cochrane, Gibson et al. 2019

According to the research teams at Cochrane, despite the large number of studies on the effectiveness of TENS, the quality of evidence is unfortunately not sufficient to draw definitive conclusions about its usefulness.

Other literature reviews

To complete this overview of the scientific literature on the effectiveness of TENS, I also searched for recent literature syntheses conducted by research teams other than those from the Cochrane Collaboration.

Three publications particularly caught my attention.

Results published in 2021 by a research team from the United Kingdom

The team analyzed the findings of 169 literature reviews and 49 meta-analyses on TENS. Here’s what they found based on the conclusions of all these studies:

• 69 out of 169 reviews showed an advantage of TENS.
• 13 out of 169 reviews showed no advantage.
• The majority of reviews (87 out of 169) showed inconclusive evidence.

Only three meta-analyses had sufficient data to inspire confidence in their results. They concluded that people using TENS had less intense pain compared to the control group for individuals with chronic musculoskeletal pain and labor pain during childbirth. After surgery, TENS users required fewer pain medications. However, the studies included in the meta-analyses were still of low quality, which limited confidence in their results.

Nevertheless, these results led the research team to recommend the use of TENS.

(Johnson, 2021)

Publication by a researcher from the United Kingdom in 2021

The first author of the previous publication wrote an article proposing three possible scenarios to finally advance our knowledge on TENS after 50 years of studies that haven’t yielded significant results. Here are the three scenarios:

1. Conduct large-scale randomized controlled trials simultaneously in multiple medical centers, identifying individuals more likely to respond well to TENS and personalizing its usage to the maximum extent.
2. Conduct good-quality meta-analyses of these well-conducted new studies, regardless of the cause of pain.
3. Accept that it will be forever impossible to determine the effectiveness of TENS due to insurmountable methodological, logistical, and financial factors.

Here is the author’s conclusion:

“I argue that patients will continue to use TENS independently of the opinions of clinicians, decision-makers, funders, or recommendations from expert groups, because TENS is readily available over-the-counter; TENS generates a pleasant sensory experience that is akin to pain relief using warming and cooling techniques; and technological developments such as smart, wearable TENS devices will improve ease of use in the future.
Therefore, research is needed to determine how best to integrate TENS into existing pain management strategies by analyzing usage data of TENS experts in real-world contexts.”

Johnson, 2021b

Publication by a research team from the United States in 2014

This research team also acknowledges the uncertainty regarding the effectiveness of TENS, although they are slightly more optimistic than the previous cited research teams. However, they propose some suggestions based on study findings to maximize the chances of TENS being effective.

Here are the key takeaways:

• Apply TENS at the maximum tolerable intensity without causing pain.
• If individuals are taking opioid medications, it is preferable to use high-frequency TENS. In other cases, whether it is high-frequency or low-frequency doesn’t matter.
• To maintain the effectiveness of TENS for as long as possible and prevent tolerance from developing, it is important to frequently vary the intensity and application frequency.

(Vance, 2014)

Despite 50 years of clinical studies and over 1500 academic publications, it has not been possible to conclusively determine the benefits or risks of TENS for chronic pain. However, it appears to be more effective for acute pain. Since it is easy to use, accessible without a prescription, has few side effects, and often provides a pleasant sensory experience, it continues to be used and desired.

What are the side effects of TENS therapy?

To obtain the most accurate understanding of the side effects of TENS machine, I revisited the results of the study syntheses conducted by the Cochrane Collaboration.

This association, which I have mentioned before, is known for its rigor. It pays careful attention to consider both the positive and negative effects of treatments. Here’s what it tells us about the side effects of TENS.

a minority of included studies provided data on adverse events (typically minor skin irritation at site of application) while the remaining studies either explicitly reported no adverse events or included studies in which no details of adverse events were provided.
One study in one review reported one incident of severe dermatitis in a participant in the sham TENS group.

Gibson 2019

Another research team recently compiled in 2022 all the known side effects of TENS.

Side effects with TENS machine are rare and minor. In the rare cases where they occur, they typically subside within minutes, hours, or days:

• Skin irritations (itchiness, redness)
• Skin rashes
• Unpleasant sensation

Source: Johnson 2022

Can TENS machine be safely used at home?

Yes, you can safely use TENS on your own at home. There have been no reported cases of serious accidents associated with the use of TENS, despite over 50 years of research and daily use by thousands of people.

Simply read the user manual carefully. If you need reassurance, you can request to have your first session with a physical therapist (either at home or in a clinic) who will show you how to use your device.

There are very few side effects associated with improper use of TENS.

See on Amazon the home TENS machine with the best value for money.

What type of electrotherapy device should be used at home?

There are numerous models available. If you are unsure about which one to choose, you can seek advice from a pharmacy, a medical or paramedical equipment retailer, or even your physical therapist.

Keep in mind one thing: there is no evidence supporting the superior effectiveness of one type of device over another (Johnson 2021).

Be careful: if your goal is to alleviate your pain, you should opt for a TENS electrotherapy device, rather than a device aimed at muscle strengthening (often referred to as an electrical stimulator). Some electrical stimulators also include TENS functionality, so you may consider purchasing those, but they may come at a higher cost.

Are TENS machine used by physiotherapists more effective?

No. The 50 years of studies conducted on the effectiveness of TENS do not suggest that certain devices are more effective than others (Johnson 2021). As long as we are certain that TENS technology is being used, it can be utilized.

There may be benefits to receiving physical therapy for the following reasons:

• Physical therapists can show you how to properly use the device initially.
• They can suggest other non-pharmacological pain treatment options.
• They can help assess the effectiveness of TENS by monitoring the qualitative and quantitative changes in your pain.
• They can encourage you to adopt behaviors that may reduce your pain in the short, medium, or long term (for example, engaging in more physical activity).

The act of someone listening to you, understanding your pain, providing solutions, and being empathetic can enhance the effectiveness of the treatment. This is known as the placebo effect, or context-related effects. The TENS devices used by physical therapists are not more effective than those used at home.

What are the contraindications of TENS machine?

There are few contraindications to the use of TENS:

• Severe psychiatric disorder.
• If you have an active implanted medical device (such as a cardiac pacemaker or other device, consult your cardiologist).
• During an electrocardiogram (ECG) procedure.
• In the case of thrombosis or phlebitis.

It should not be used (as a precaution) on these body parts:

• On the neck (but it is possible on the nape of the neck).
• On the chest (but it is possible on the lower abdomen, especially for menstrual pain or pain during labor).
• On the entire abdomen of a pregnant woman.
• On the carotid sinuses.
• On damaged (wounded, burned) or desensitized skin (for example, due to a neurological issue).

The main contraindication of TENS is the use of an active implanted device (such as a pacemaker).