Pamprin Heat Relief Menstrual Heat Patches are drug-free, odor-free contoured heat patches that provide relief from period pain – both cramps and backaches. They are single use, air activated heat patches that provide up to 12 hours of pain relief by increasing blood flow which relaxes muscles and tension for soothing relief. These pain relief patches provide on the go relief with a large contoured design – yet are discreet and thin for convenience and comfort.