Key messages
• Overall, both high-frequency and low-frequency transcutaneous electrical nerve stimulation (TENS) may reduce pain compared with placebo (dummy treatment) or no treatment.
• We are uncertain about the effects of high-frequency TENS compared with low-frequency TENS, the effects of both high- and low-frequency TENS compared with other treatments (acupressure, acetaminophen, interferential current therapy), and unwanted effects.
• Future studies should investigate unwanted effects, and also the effectiveness of TENS on the need to use additional painkillers, daily activities limited by pain, and quality of life. Studies should involve more women and use robust methods.
What is period pain?
Period pain is cramps in the uterus and pain or a constant ache in the lower stomach and the lower back and legs. It usually occurs at the beginning of a monthly period (menstruation). It is very common in women and girls of childbearing age. Many women take over-the-counter painkillers, such as ibuprofen and acetaminophen (paracetamol). However, some women cannot use these medicines due to unwanted effects, or other health problems.
What is TENS (transcutaneous electrical nerve stimulation) and how might it help?
A TENS machine is a small, portable device with pads (electrodes) that stick to the skin over the source of pain. It is usually used by women themselves, at home, when they start to experience pain. The machine sends a small electrical current through the skin to the affected area, which may give a tingling sensation. TENS doesn't stop cramps or pain, but it is thought that the current blocks pain signals from nerves to the brain, which reduces the feeling of pain. TENS may also help the body to produce 'endorphins', which are the body's natural painkillers. TENS is inexpensive and may have fewer unwanted effects than medications. Unwanted effects may include slight redness or irritation of the skin around the electrodes. It is possible to vary the frequency and strength of the electrical current, described as high-frequency TENS or low-frequency TENS.
What did we want to find out?
We wanted to find out if TENS can relieve period pain without causing unwanted effects. We were interested only in the effects of TENS on women whose pain was caused by periods, not due to any other condition. We wanted to know if high-frequency TENS was more effective than low-frequency TENS, and whether TENS was more effective than a placebo (dummy) treatment or no treatment, or other treatments for period pain.
What did we do?
We searched for studies that investigated high- or low-frequency TENS compared with a placebo or no treatment, or another treatment. Studies could take place anywhere in the world as long as they included women and girls with period pain.
What did we find?
For this review, we included 20 studies with 585 women with period pain. Studies were published between 1985 and 2019. They mostly took place in Brazil, the USA and Sweden, with others in South Korea, Japan, Iran, Norway, Turkey, Taiwan and India.
• High-frequency TENS compared with placebo or no treatment may reduce pain (10 studies, 345 women) but we don't know if there is any difference in unwanted effects (3 studies, 146 women).
• Low-frequency TENS compared with placebo or no treatment may also reduce pain (3 studies, 645 women). No studies reported unwanted effects.
• High-frequency TENS compared with low-frequency TENS: we don't know which has more effect on pain (3 studies, 54 women). One study reported that no unwanted effects occurred.
• High-frequency TENS compared with other treatments: the only other treatments we found were acupressure (1 study, 18 women), acetaminophen (paracetamol)(1 study, 20 women), and 'interferential current therapy', which is similar to TENS but with a stronger electrical current (2 studies, 62 women). We don't know if there was any difference between high-frequency TENS and these treatments. There may be no difference in unwanted effects.
• Low-frequency TENS compared with other treatments: the only other treatment we found was acetaminophen (1 study, 20 women). We don't know if there was any difference between the two treatments. No studies reported unwanted effects.
What are the limitations of the evidence?
Overall, our confidence in the evidence was low to very low. This was mainly because we found a small number of studies, and they did not include many women. In particular, unwanted effects were poorly reported in most studies.
How up to date is the evidence?
This new review replaces a review published in 2009. The evidence is up to date to April 2024.
High-frequency TENS and low-frequency TENS may reduce pain compared with placebo or no treatment. We downgraded the certainty of the evidence because of the risk of bias. Future RCTs should focus more on secondary outcomes of this review (e.g. requirement for additional analgesics, limitation of daily activities, or health-related quality of life) and should be designed to ensure a low risk of bias.
Transcutaneous electrical nerve stimulation (TENS) is a non-pharmacological treatment that works by delivering electrical currents via electrodes attached to the skin at the site of pain. It can be an alternative to pharmacological treatments. The mechanism of action of TENS for pain relief is related to the inhibition of the transmission of painful stimuli, release of endogenous opioids, and reduced muscle ischaemia of the uterus. Although it has been used for primary dysmenorrhoea ((PD); period pain or menstrual cramps), evidence of the efficacy and safety of high-frequency TENS, low-frequency TENS, or other treatments for PD is limited.
To evaluate the effectiveness and safety of transcutaneous electrical nerve stimulation (TENS) in comparison with placebo, no treatment, and other treatments for primary dysmenorrhoea (PD).
We searched the Gynaecology and Fertility Group’s Specialized Register of controlled trials, CENTRAL, MEDLINE, Embase, PsycINFO, AMED, CINAHL, and the Korean and Chinese language databases up to 9 April 2024. We also searched for ongoing trials in trials registries and the reference lists of relevant studies for additional trials. Language restrictions were not applied.
We included randomized controlled trials (RCTs) that included women (aged 12 to 49 years) with PD. Included trials compared low-frequency TENS or high-frequency TENS with other TENS, placebo, or other treatment.
Four review authors screened the trials, extracted the data according to the protocol, assessed the risk of bias using RoB 2, and assessed the certainty of evidence for all review comparisons and primary outcomes (i.e. pain relief and adverse effects) using the GRADE approach.
This review replaces the current review, published in 2009. We included 20 RCTs involving 585 randomized women with high−frequency TENS, low−frequency TENS, placebo or no treatment, or other treatment.
We included five comparisons: high−frequency TENS versus placebo or no treatment, low-frequency TENS versus placebo or no treatment, high-frequency TENS versus low-frequency TENS, high-frequency TENS versus other treatments, and low-frequency TENS versus other treatments.
High-frequency TENS versus placebo or no treatment
High-frequency TENS may reduce pain compared with placebo or no treatment (mean difference (MD) −1.39, 95% confidence interval (CI) −2.51 to −0.28; 10 RCTs, 345 women; low-certainty evidence; I2 = 88%). Two out of three RCTs reported no adverse effects and hence we were unable to estimate the effect of high-frequency TENS on adverse effects.
Low-frequency TENS versus placebo or no treatment
Low-frequency TENS may reduce pain compared with placebo or no treatment (MD −2.04, 95% CI −2.95 to −1.14; 3 RCTs, 645 women; low-certainty evidence; I2 = 0%). No trials reported adverse effects for this comparison.
High-frequency TENS versus low-frequency TENS
It is uncertain whether high-frequency TENS had an effect on pain relief compared with low-frequency TENS (MD 0.89, 95% CI −0.19 to 1.96; 3 RCTs, 54 women; low-certainty evidence; I2 = 0%). One trial contributed data on adverse effects but no adverse events occurred.
High-frequency TENS versus other treatments
It is uncertain whether high-frequency TENS had an effect on pain relief compared to acupressure (MD −0.66, 95% CI −1.72 to 0.40; 1 RCT, 18 women; very low-certainty evidence), acetaminophen (paracetamol) (MD −0.98, 95% CI −3.30 to 1.34; 1 RCT, 20 women; very low-certainty evidence), and interferential current therapy (MD −0.03, 95% CI −1.04 to 0.98; 2 RCTs, 62 women; low-certainty evidence; I2 = 0%). The occurrence of adverse effects may not differ significantly between high-frequency TENS and NSAIDs (OR 12.06, 95% CI 0.26 to 570.62; 2 RCTs, 88 women; low-certainty evidence; I2 = 78%).
Low-frequency TENS versus other treatments
It is uncertain whether low-frequency TENS had an effect on pain relief compared with acetaminophen (MD −1.48, 95% CI −3.61 to 0.65; 1 RCT, 20 women; very low-certainty evidence). No trials reported adverse effects for this comparison.