Progesterone (Cyclogest)
Is It Right for You?
A complete guide to Progesterone (Cyclogest) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Cyclogest?
Cyclogest is a brand of natural (micronised) progesterone formulated as a suppository (pessary) for vaginal or rectal administration. Each pessary contains 200 mg or 400 mg of progesterone. Unlike synthetic progestogens (progestins) used in many hormone replacement therapy and contraceptive products, Cyclogest contains bio-identical natural progesterone — chemically identical to the progesterone produced by the ovaries and adrenal glands.
Cyclogest is used in a range of clinical contexts requiring progesterone supplementation: as luteal phase support in assisted reproduction (IVF and other ART cycles), as part of hormone replacement therapy in peri- and post-menopausal women using oestrogen-based HRT, and in the management of premenstrual syndrome. It provides progesterone via the vaginal or rectal route, which achieves high local and systemic bioavailability while bypassing the first-pass hepatic metabolism that significantly reduces the bioavailability of oral progesterone.
Cyclogest is a prescription-only medication in the UK. A licensed clinician must assess your clinical situation and hormonal requirements before it can be prescribed — which can now be done quickly and conveniently through a telehealth consultation.
What Conditions Is Cyclogest Used For?
Cyclogest is licensed for and prescribed in:
supplementing or replacing the progesterone normally produced by the corpus luteum following egg retrieval, to support endometrial receptivity and early embryo implantation.
to supplement progesterone levels in the luteal phase and alleviate physical and psychological PMS symptoms.
as the progestogen component of combined HRT in post-menopausal women who have a uterus; protects the endometrium from the proliferative effects of unopposed oestrogen.
increasingly used to support early pregnancy in women with a history of recurrent miscarriage or threatened miscarriage with confirmed intrauterine pregnancy.
Cyclogest contains bio-identical natural progesterone, which differs structurally and pharmacologically from synthetic progestogens (progestins) such as norethisterone or medroxyprogesterone acetate used in many oral contraceptive pills and older HRT preparations. Natural progesterone has a more favourable cardiovascular and breast safety profile in HRT and does not carry the same risks as some synthetic progestogens.
How Does Cyclogest Work?
Progesterone is the primary endogenous progestogen — a steroid hormone produced primarily by the corpus luteum after ovulation and, in pregnancy, by the placenta from approximately 8 to 10 weeks of gestation. It exerts its effects by binding to intracellular progesterone receptors (PRs), causing receptor-DNA complexes to modulate the transcription of progestogen-responsive genes.
In the context of assisted reproduction and early pregnancy, progesterone's key actions are:
Endometrial Transformation — Progesterone converts the proliferative (oestrogen-primed) endometrium into a secretory endometrium with abundant glycogen-rich glands, creating a receptive environment for embryo implantation.
Cervical Mucus Thickening — Progesterone causes thickening of cervical mucus, reducing ascending infection risk.
Myometrial Quiescence — Progesterone inhibits uterine contractility, maintaining a stable uterine environment conducive to early pregnancy.
Endometrial Protection in HRT — In post-menopausal women taking oestrogen-based HRT, progesterone prevents oestrogen-induced endometrial hyperplasia and endometrial carcinoma.
Vaginal or rectal administration achieves a "uterine first-pass effect" via direct absorption from the vaginal or rectal venous plexuses, achieving high local progesterone concentrations in the uterus while minimising systemic levels — reducing systemic sedative side effects compared to oral progesterone.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Insert the pessary as deep as possible into the vagina using a clean finger, preferably while lying down. For rectal administration, insert into the rectum similarly.
Use vaginally where possible — vaginal administration achieves higher uterine progesterone concentrations via the uterovaginal circulation, making it preferable for IVF luteal support and threatened miscarriage. Rectal administration may be preferred if vaginal application is uncomfortable or contraindicated.
Insert at night when possible — lying down after insertion reduces the loss of dissolved pessary from the vagina and maximises absorption.
A waxy residue from the pessary base may be noticed in underwear — wearing a panty liner can help manage this.
Wash hands before and after insertion.
Do not use during menstruation unless specifically directed — for IVF and HRT cycles, your clinician will specify the exact timing.
Side Effects of Cyclogest
Cyclogest is generally well tolerated. Because progesterone is delivered vaginally or rectally, systemic levels are lower and sedative side effects are reduced compared to oral progesterone.
- Vaginal or rectal irritation, leakage, or discomfort
- Waxy discharge from pessary base
- Bloating and breast tenderness
- Drowsiness or sedation (lower than with oral progesterone but possible, particularly with rectal use)
- Mood changes (low mood, irritability)
- Headache
- Nausea
- Constipation
- Venous thromboembolism — natural progesterone carries a lower VTE risk than synthetic progestogens, but some risk exists, particularly when used with oestrogen in HRT
- Severe allergic reaction — rare; contact dermatitis or systemic hypersensitivity
- Ectopic pregnancy rupture — progesterone support does not prevent ectopic pregnancy; if abdominal pain or abnormal bleeding occurs in early pregnancy, urgent assessment is required to exclude ectopic pregnancy
Progesterone support does not prevent or cause ectopic pregnancy, but it maintains uterine secretory changes and luteal function even if an ectopic pregnancy is present. Women undergoing IVF or early pregnancy support must have an early ultrasound to confirm intrauterine pregnancy before progesterone support is continued.
Drug Interactions
Natural progesterone has a limited systemic drug interaction profile compared to synthetic progestogens. Relevant interactions include
Progesterone may modestly alter coagulation; INR monitoring is advisable in anticoagulated patients on HRT.
May accelerate progesterone metabolism, reducing its efficacy; dose adjustment may be necessary.
Progesterone has mild sedative properties; additive sedation with alcohol, benzodiazepines, or other CNS depressants is possible, particularly with rectal administration.
Important Warnings
Cyclogest is not a contraceptive. It will not prevent pregnancy. In IVF cycles it is used precisely to support implantation and early pregnancy.
Women using Cyclogest for threatened miscarriage or recurrent miscarriage support require regular ultrasound monitoring to confirm ongoing intrauterine pregnancy and fetal viability.
The safety of progesterone in women with a current or recent history of breast cancer should be discussed with an oncologist before starting Cyclogest.
Cyclogest is specifically prescribed to support pregnancy. The safety of progesterone in early pregnancy has been extensively studied and it is not associated with teratogenicity at therapeutic doses
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Cyclogest FAQs
Oral progesterone is subject to extensive first-pass liver metabolism, meaning very little reaches the bloodstream after absorption from the gut. To achieve therapeutic systemic and uterine levels, very large oral doses would be needed — and even then, the pharmacokinetics are variable. Vaginal administration bypasses first-pass metabolism and achieves a "uterine first-pass effect" — high local progesterone concentrations in the uterus via the uterovaginal portal circulation — making it the gold standard for luteal phase support in IVF.
Current evidence suggests natural (micronised) progesterone has a more favourable safety profile than many synthetic progestins in the context of HRT — particularly regarding breast cancer risk and cardiovascular effects. The Menopause Society and many European guidelines now recommend micronised progesterone as the preferred progestogen component of HRT in women with a uterus. Your clinician can discuss the evidence in detail in relation to your personal health history.
Clinical evidence from the PRISM trial and PROMISE trial showed that progesterone supplementation in early pregnancy significantly reduces miscarriage rates in women with a history of previous miscarriage who present with early pregnancy bleeding. For women with recurrent miscarriage (3 or more pregnancy losses), progesterone supplementation is recommended. It does not prevent all miscarriages, particularly those due to chromosomal abnormalities.