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Recurrence of Endometriosis: A randomised controlled trial of clinical and cost-effectiveness of Gonadotrophin Releasing Hormone Analogues with add-back hormone replacement therapy versus repeat Laparoscopic surgery

What is Regal?

Endometriosis is a common condition which affects one in ten women from puberty to menopause. It occurs when cells similar to those lining the womb grow outside it, generally within the pelvis. These cells behave like the cells lining the womb, causing internal bleeding at the time of periods, scarring and pain.

Endometriosis is diagnosed by laparoscopy (keyhole surgery) which identifies areas of endometriosis which can then be destroyed or removed. However, surgery rarely provides lasting relief and pain can return in up to half of treated women within five years. To reduce the chance of regrowth of endometriosis and recurrence of pain, women who are not trying to get pregnant are offered the combined oral contraceptive pill or other contraceptives containing hormones called progestogens.

Despite this, about one in three women will require more operations to treat endometriosis that has come back.

Endometriosis depends on the female hormone oestrogen (produced by the ovaries) for growth. Removing the ovaries (often along with the womb) therefore provides the best chance of pain relief and least chance of more operations but is not an option for many premenopausal with endometriosis.

A less invasive way of shrinking endometriosis is to use a drug called Gonadotrophin Releasing hormone analogue (GnRHa) which temporarily stops the ovaries from producing oestrogen. While very effective in terms of reducing pain, this treatment has only been used for up to a year because of side effects such as hot flushes and night sweats and concerns about osteoporosis (thinning of the bones). Recent research has shown that adding small doses of hormone replacement therapy (HRT) in women on GNRHa reduces the risk of side effects and osteoporosis whilst controlling the pain.

REGAL trial is comparing long-term GnRHa with added HRT to further keyhole surgery for treatment of endometriosis in women who experience recurrence of pain after surgery but wish to preserve their fertility.

Can I take part?

You may be eligible to take part in REGAL if:

•     you are female and aged between 21-49 years old
•     you have recurrent pain following laparoscopic treatment for endometriosis
•     you wish to avoid removal of your ovaries and a hysterectomy
•     your doctor considers you suitable for both study arms (Gonadotrophin Releasing hormone analogue (GnRHa with HRT versus further laparoscopic surgery)

Please see ‘Where can I take part?’ to check if your local hospital is participating.


If you would like to know more about REGAL, including information about taking part, please contact the study office at the University of Aberdeen on 01224 438196 or email

If you are interested in taking part, or have any questions?

Where can I take part?


Key people:



Respiratory Unit, Clinic C
Aberdeen Royal Infirmary
AB25 2ZN

Study news



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Key facts about the study and documents

What is this study about?

If you are eligible and wish to participate in REGAL and your hospital is a recruiting site, you will receive further information from your local research team.

To take part you will be asked to sign the study consent form and complete a questionnaire about your pain and quality of life. After this, the local research nurse will randomise you into the study i.e. you will be allocated (at random) to receive one of the treatments below:

•     Gonadotrophin Releasing hormone analogue (GnRHa) with HRT
•     Further laparoscopic surgery

We will regularly follow your progress for 24 months.

We will send you the study questionnaire through the post (or email if you prefer) at 6, 12, 18 and 24 months from the date you entered the study. The questionnaires are returned to the study office in a prepaid envelope which we provide.

You can find out more information about Regal here:

Download documents:

Key contacts

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Funding acknowledgement

The project is funded by the National Institute for Health Research (NIHR) Health Technology Assessment (HTA) programme (reference NIHR127280) and run by the University of Aberdeen, in conjunction with NHS Grampian. The views expressed are those of the author(s) and do not necessarily those of the NHS, the NIHR or the Department of Health & Social Care.