LOCI: Letrozole Or Clomifene for Ovulation Induction

  • Research type

    Research Study

  • Full title

    Letrozole or Clomifene, with or without metformin, for ovulation induction in women with polycystic ovary syndrome: a 2x2 factorial design randomised trial (The LOCI trial)



  • Contact name

    Arri Coomarasamy

  • Contact email


  • Sponsor organisation

    University of Birmingham

  • Eudract number


  • ISRCTN Number


  • Duration of Study in the UK

    2 years, 9 months, 1 days

  • Research summary

    Polycystic ovary syndrome (PCOS) affects 20% of women. Women with PCOS may not release eggs from their ovaries; this is called anovulation. The first line treatment for anovulation is a medicine called clomifene (formerly known as clomiphene). Current clinical guidelines in the UK recommend the use of clomifene with or without another medicine, metformin, for a maximum of 6 menstrual cycles. Clomifene treatment does not result in pregnancy for approximately 70% of women despite prolonged treatment. Furthermore, clomifene is associated with numerous side effects and a 10-fold increase in the risk of multiple pregnancy.
    Recently there has been growing interest in the use of another medicine, letrozole, to treat infertility in women with PCOS. Letrozole works differently to clomifene and has fewer side effects, including a lower risk of multiple pregnancy. A recent review of studies involving all available medicines for women with PCOS and infertility has indicated that letrozole may be more effective than clomifene when used alone, and there may be additional value when it is combined with metformin.
    This trial has been developed in consultation with two patient representation groups, Fertility Network UK and the Women’s Network of the RCOG. We plan to ask women diagnosed with PCOS seeking fertility treatment to participate in this study. Participants will be allocated to clomifene or letrozole, which they will take for 5 days at the beginning of each menstrual cycle. Participants will also be given metformin or a dummy drug to be used alongside clomifene or letrozole but this use will continue up until the first 14 weeks of pregnancy. Clomifene or letrozole treatment will be offered for up to 6 treatment cycles, to match the current guidelines. The allocation of treatment will be decided at random by a computer, and neither the participants nor the researchers will know what treatment a patient is receiving; this arrangement is necessary to test the treatments fairly. The main outcome evaluated will be whether a participant has a live birth. A number of other key outcomes such as ovulation rate, miscarriage, multiple pregnancy and newborn outcomes will also be assessed.

  • REC name

    West Midlands - Edgbaston Research Ethics Committee

  • REC reference


  • Date of REC Opinion

    3 Feb 2020

  • REC opinion

    Further Information Favourable Opinion

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