A single-centre, randomised controlled, double blind study comparing use of the Allay pulsed shortwave therapy treatment versus a placebo device or no treatment for management of primary dysmenorrhea.

Women participating in the trial will be randomly allocated to any of the three arms of the study.

• Treatment for 2 menstrual cycles using the PSWT Allay device (BioElectronics Corp, Frederick USA)
• Treatment for 2 menstrual cycles using a placebo device
• No treatment. If they are allocated to a device both the participant and the clinician will be blinded at to weather they are using the active device or the placebo.

Primary Outcome measures are:

• A reduction in dysmenorrhea as measured by the highest pain score on a 10cm visual analogue scale.

• A reduction in average pain score on a 10cm visual analogue scale

• A reduction in use of analgesia as recorded in a pain diary

• Improvement in quality of life as measured through a validated quality of life assessment tool (SF-36 questionnaire)

  - Improvement in menstrual symptoms as recorded through a validated questionnaire (the Modified Menorrhagia Multi-attribute Scale (MMAS)).

• Device acceptability as measured on a 5-point Likert scale ranging from "unacceptable" to "totally acceptable".

• Impact upon associated cyclical symptoms as recorded in a patient symptom diary

Inclusion Criteria:

• Female with persistent (>3months) cyclical period pain associated with menstruation (defined as 5 or more on VAS).
• Able to give written, Informed consent
• Able to wear device and keep up-to-date records of use
• Agrees to attend follow up
• If currently using hormonal contraception agrees to continue on the same dose for the duration of the trial.

Exclusion Criteria:

• Age under 16 years.
• Trying to conceive or <6 weeks post partum
• Currently participating or planning to participate in another clinical trial

Participants will be randomly allocated to a treatment arm through telephone randomisation. If they are allocated to "no treatment" they will be aware of the management, however if allocated to use of a device the participant and care provider will be blinded to weather it is an active device or placebo device. The outcome assessor will be blinded to the treatment allocation.