Period cramps (primary dysmenorrhea) are usually caused by uterine muscle contractions driven by prostaglandins, especially during the first one to two days of bleeding. When prostaglandin levels are high, the uterus can contract more strongly and irregularly, which can reduce blood flow and trigger pain.

This is why cramps can come with nausea, fatigue, and headaches, and why they can disrupt school or work. Good treatments either reduce prostaglandins, reduce the pain signal, or help the body relax during the cramping window.

Heat pads are one of the most proven non-drug options. A well-designed clinical trial compared a continuous low-level heat patch with ibuprofen and placebo and found that heat was as effective as ibuprofen for menstrual pain relief over two days.

The heat patch meaningfully improved pain compared with placebo, and combining heat with ibuprofen shortened the time to noticeable relief, even though total relief over two days was not dramatically better than ibuprofen alone.

Heat likely works by relaxing muscles, improving local blood flow, and reducing the nervous system’s pain sensitivity—simple mechanisms that match how many people experience relief.

Electrical “period cramp machines” are usually closer to TENS (transcutaneous electrical nerve stimulation) than to EMS. TENS is designed mainly for pain relief by changing how pain signals are processed, not by forcing strong muscle contractions. A Cochrane review found that high-frequency TENS was more effective than placebo TENS for pain relief in primary dysmenorrhea, while low-frequency TENS did not outperform placebo in the available trials. This matters because many consumer devices don’t clearly explain whether they are using high-frequency pain-focused stimulation or low-frequency muscle-twitch stimulation.

Vibration-based pads may help some people feel better through comfort, distraction, and muscle relaxation, but your sources provide stronger evidence for heat and high-frequency TENS than for vibration alone. If a device combines vibration with heat, the heat is likely doing most of the proven “heavy lifting.” As for EMS, it’s different: EMS is intended to create muscle contractions.

Cramps come from the uterus contracting internally, and surface EMS cannot directly “train” or control uterine contractions. In practice, period devices that claim “EMS for cramps” may actually be using TENS-like settings aimed at pain gating rather than true muscle-building stimulation—so it’s important to look for TENS-style claims and settings rather than “muscle stimulation” marketing.

Beyond gadgets, the most evidence-supported approach is still medical first-line treatment when appropriate: NSAIDs (like ibuprofen or naproxen) reduce prostaglandins and help up to about 70% of people, according to clinical guidance, and combined oral contraceptives can reduce prostaglandin production by limiting endometrial growth.

A systematic review and meta-analysis also found that exercise showed large effects on menstrual pain, while heat and acupressure showed moderate effects, with exercise and heat sometimes comparing favorably against analgesics in pain intensity outcomes. The most reliable plan is a layered one: early NSAID use (if safe for you), plus heat, plus movement, plus a pain-focused device like high-frequency TENS if needed.