What is Micronor?

Micronor is a mini pill - it contains progestogen only - whereas the combined oral contraceptive pill contains oestrogen and a progestogen.

Picture of Micronor

Table 14.1  Mini pills.


Progestogen  (microg)


Cerazette Desogestrel 75 micrograms Organon
Femulen Ethynodiol diacetate 500 Searle
Micronor Norethisterone 350 Janssen-Cilag
Norgeston Levonorgestrel 30 Schering
Noriday Norethisterone 350 Searle

How does Micronor provide contraception?

Micronor prevents the cervical mucus changes around the time of ovulation so that sperm cannot get through to the egg thus preventing fertilisation. The lining of the womb (endometrium) is affected so that, even if an egg is fertilised, it is unlikely to be able to implant and develop.

The combined oral contraceptive pill (COP), with occasional exceptions, prevents egg release (ovulation). It is now recognised that the mini pill also interferes with ovulation although not as effectively as COPs.

How do mini pills compare to combined Pills?

Table 14. 2. A comparison between mini pills and combined oral contraceptive pills.

Mini pills (Progesterone only  pills) Combined pills (COPs)
Alternative when COPs have side effects (Q15.7)
Alternative when COPs contraindicated (8) New low dose pills have fewer side effects.
Excellent contraception (Table 14.1). More effective than mini pills (Table 14.1.
Very effective when breast feeding. Not recommended when breast feeding.
Very effective beyond the age of 40 years. Acceptable up to the menopause (but see 25.
No benefits to cycle control. Excellent cycle control and reduced bleeds.
Timing of bleeds cannot be adjusted.

When are Mini Pills preferred to the combined oral contraceptive pill (COP)?

  • For medical disorders where COPs are only prescribed with caution e.g. for diabetic patients (7 ).
  • If COPs are contraindicated e.g. history of thromboembolism (8)
  • If several combined pills are associated with side effects (Q15.7)
  • High blood pressure.
  • Severe migraine.
  • Obesity (seeQ14.8)
  • Breast feeding.
  • Sickle cell disease.
  • Cigarette smokers from age 35 years.

How effective is micronor?

This depends on patient compliance and age. The quoted results vary from 0.3 to 4 per hundred women years (Q13.6).

Micronor is very effective during breast-feeding.

Failure rates may be higher if you are overweight; if you are heavier than 11 stones (70KG) it is advisable to take two pills daily.

When should Micronor be started and when does it become effective?

Micronor can be commenced on the first day of a period and it will then provide immediate protection.

What should I do if I miss a Micronor pill?

A Micronor pill should be regarded as missed if it is taken more than three hours late. The manufacturers indicate, that if Micronor is taken late, additional precautions are required for seven days.

Emergency contraception ((Q17.23) may be required.

What will happen to my periods when I take Micronor?

It is likely that they will continue as before but there is no consistent pattern. You may experience breakthrough bleeding between the periods initially and there is a chance that your periods may become lighter or occasionally stop.

What should I do if my periods stop whilst I am taking Micronor?

Provided the rules relating to taking the pill are obeyed pregnancy is unlikely.

Pregnancy should be excluded by a pregnancy test.

If you think you may be reaching your menopause, a hormone test may be helpful (14).

Otherwise, there is no problem from the medical point of view. If you find it disconcerting not to see a period or you keep worrying about pregnancy you may need to consider a different form of contraception.

What should i do if i vomit whilst taking Micronor?

If this happens within two hours of taking the pill another should be taken. If another pill is not taken within this time additional precautions are required throughout the illness and for a further seven days.

Should additional precautions be taken when i am on antibiotics?

The only antibiotics that definitely necessitate additional precautions are rifampicin and griseofulvin.

If you need to take these drugs long-term, you will require a different method of contraception.

No special action is required with other antibiotics.

Can Micronor cause ovarian cysts?

Functional cysts (88), but not true ovarian cysts, occur more frequently amongst those taking mini pills.

If a woman taking Micronor develops pain and a period is late the question of an ectopic pregnancy has to be addressed.

At one time laparoscopy was required to exclude the diagnosis.

For nearly twenty years, we have had Beta HCG (pregnancy) tests, which are extremely sensitive; if the test is negative, an ectopic can be excluded. Unless there are severe symptoms, functional cysts can be left alone and they will regress over the course of a few weeks.

Should I stop taking my Micronor before surgery?

There is no reason for Micronor to be discontinued. The advice with the mini pill differs from that with the combined pill ((23).


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Women's Health

This is the personal website of David A Viniker MD FRCOG, retired Consultant Obstetrician and Gynaecologist - Specialist Interests - Reproductive Medicine including Infertility, PCOS, PMS, Menopause and HRT.
I do hope that you find the answers to your women's health questions in the patient information and medical advice provided.

I do hope that you find the answers to your women's health questions in the patient information and medical advice provided.

Answers to FAQs on women's health, patient information and medical advice by David A Viniker MD FRCOG, Consultant Obstetrician and Gynaecologist (Gynecologist - OBGYN), Department of Obstetrics and Gynaecology, , London

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