Medicines Information Skills for
NHS Direct Nurse Advisors & Health Information Advisors
Oral Contraceptives
Objectives
After
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completing this session, you should
be familiar with the different types of oral contraceptives that are available
understand how oral contraceptives work
be able to advise NHS Direct callers regarding
o
o
o
o
o
missed pills
taking the wrong pill from the packet
taking too many pills
drug interactions with the pill
where to obtain emergency hormonal contraception
Oral Contraception
Oral contraception was introduced over 40 years ago and has remained extremely popular due to
its convenience and effectiveness.
There
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are three main types of oral contraceptives:
combined oral contraceptive (COC)
progestogen only pill (POP)
emergency hormonal contraceptive (EHC)
Combined Oral Contraceptive (COC)
COCs are the most commonly used oral contraceptive pills. Worldwide there are currently
around 100 million women using COCs. In the UK there are over 3 million COC users with nearly
four out of five women having used it at some time during their reproductive years.
COCs are combinations of oestrogen (usually ethinylestradiol) and a progestogen. There are 25
different COCs listed in BNF (edition 51). They are taken for 21 days followed by a seven-day
pill free period or 7 days placebo tablets (ED). The COC is the most effective preparation for
general use; with optimal use it is more than 99% effective. With sub-optimal use, failure rates
can be as high as 8%.
The COC preparations can be divided into three groups: monophasic, biphasic and triphasic.
The monophasic preparations contain a fixed amount of oestrogen and progestogen in each
active tablet. E.g. Mercilon, Eugynon 30, Microgynon 30, Ovranette.
The biphasic and triphasic pills contain varying amounts of the two hormones according to the
stage of the cycle. The aim is that the hormones imitate the normal monthly hormonal
variations more closely, although there is no evidence that this is better for general health.
Women tend to get heavier withdrawal bleeding with these preparations. The only biphasic
preparation available is Binovum. Examples of triphasic preparations are Logynon, Trinordial,
Synphase, Trinovum, Tri-Minulet, Triadene.
There are also ED (every day pills) which include seven placebo tablets, which are particularly
suitable for women who find it easier to take a pill every day, rather than having a seven day
break. Examples of ED pills include Logynon ED, Microgynon 30 ED and Femodene ED.
Oral Contraception and EHC
April 2006
Medicines Information Skills for
NHS Direct Nurse Advisors & Health Information Advisors
Progestogen Only Pill (POP)
The POP as its name suggests only contains a progestogen. There are only five preparations
listed in the BNF (edition 51), but they may offer a suitable alternative when oestrogens are
contraindicated (e.g. in breastfeeding mothers). They are taken continuously (i.e. no pill free
week). Usage of the POP is much less, accounting for no more than 10% of the UK hormonal
contraceptive market. Efficacy is dependent on the meticulousness of the user and appears to
be related to age, the failure rate being higher in the younger user.
Emergency Hormonal Contraception (EHC)
The brand name of this product is Levonelle® or Levonelle One Step®. The product consists of a
progestogen, called levonorgestrel, at quite high dose. One 1500mcg tablet should be taken as
soon as possible, preferably within 12 hours and no later than 72 hours after unprotected
intercourse. Taking the dose as soon as possible increases efficacy. The mechanism of action of
EHC depends on the point in the menstrual cycle the pill is taken, it either prevents or delays
ovulation, prevents fertilisation or prevents implantation of the fertilised egg into the uterus.
Legally in the UK a pregnancy is not recognised to exist until implantation is completed. EHC is
available from a variety of places including GPs, NHS Walk-in Centres, Family Planning Clinics,
Sexual Health Clinics, Community pharmacies and some A & E departments (although they
should be regarded as last resort).
Mechanism of Action
Ovary: the action of oestrogen at the ovary inhibits ovulation by blocking the surge of luteinizing
hormone (LH) and follicle stimulating hormone (FSH), which is essential for egg release.
Progestogens are much weaker but have the same effect. For COCs this is their most important
site of action, whereas the POP only blocks ovulation in ~25% of women (except for Cerazette®
which regularly blocks ovulation).
Fallopian Tube: progestogen inhibits motility, whereas oestrogen enhances motility, both of
which cause abnormal rates of ovum transport.
Endometrium: sustained levels of oestrogen or progestogen cause asynchronous development
that is less receptive to implantation.
Cervical Mucous: progestogen causes secretion of thick viscous mucous which is hostile to
sperm. This is the most important site of action of the POP. The effect is maximal at four hours
after taking the POP and lasts approximately 20 hours.
Missed Pills
Combined oral contraceptive
It is important to bear in mind that the critical time for loss of protection is when a pill is
omitted at the beginning or end of a cycle (which lengthens the pill-free interval). The
following is now recommended by family planning organisations:
‘Missing pills or starting the packet late may make your pill less effective. The chance
of pregnancy after missing pills depends on when pills are missed and how many pills
are missed.
Missing one pill anywhere in your pack or starting the new pack one day late is not a
problem. Depending on which type of pill you take, missing more than one or starting
the packet more than one day late may affect your contraceptive cover.
It is more risky to start a packet late or miss the first pill(s) of the next pack. This is
because during the seven day break or placebo week your ovaries are not getting any
Oral Contraception and EHC
April 2006
Medicines Information Skills for
NHS Direct Nurse Advisors & Health Information Advisors
effects from the pill. If you make the break or placebo week longer your ovaries might
release an egg.’
Progestogen Only Pill
The following advice is recommended by family planning organisations:
‘If you forget a pill, take it as soon as you remember and carry on with the next pill at
the right time. If the pill was more than three hours (12 hours for Cerazette®) overdue
you are not protected. Continue normal pill taking but you must also use another
method, such as the condom, for the next 2 days’.
The faculty of Family Planning and Reproductive Health Care recommends emergency
contraception if one or more progestogen-only contraceptive tablets are missed or taken more
than three hours late.
Background Information
Please list what background information you will require before answering an enquiry about
‘missed contraceptive pill(s)’.
Please list what background information you will require before answering an enquiry about
taking too many contraceptive pills.
Please list what background information you will require before answering an enquiry about
taking the wrong contraceptive pill out of the packet.
Oral Contraception and EHC
April 2006
Medicines Information Skills for
NHS Direct Nurse Advisors & Health Information Advisors
Diarrhoea and Vomiting
Combined Oral Contraceptive
Vomiting up to 2 hours after taking an oral contraceptive or very severe diarrhoea can interfere
with its absorption. Additional precautions should therefore be used during and for 7 days after
recovery. If the vomiting and diarrhoea occurs during the last 7 tablets, the next pill-free
interval should be omitted (in the case of ED tablets the inactive ones should be omitted).
Progestogen Only Pill
Vomiting up to 3 hours after taking a POP or very severe diarrhoea can interfere with its
absorption. Additional precautions should be used during and for 7 days after recovery.
Please list what background information you will require before answering an enquiry about
diarrhoea & vomiting when taking an oral contraceptive.
Drug Interactions
The effectiveness of both combined and progestogen-only oral contraceptives may be
considerably reduced by interaction with drugs that induce hepatic enzyme activity (e.g.
carbamazepine, griseofulvin, modafinil, nelfinavir, nevirapine, oxcarbazepine, phenytoin,
phenobarbital, primidone, ritonavir, St. Johns Wort, topiramate, and, above all, rifabutin and
rifampicin). Family Planning Association (FPA) advice regarding these drug interactions is
available in the BNF.
Some broad spectrum antibiotics (e.g. ampicillin, doxycycline) may reduce the efficacy of
combined oral contraceptives by impairing the bacterial flora responsible for recycling of
ethinylestradiol from the large bowel. FPA advice regarding these interactions is available in
the BNF.
Broad-spectrum antibiotics do not affect the effectiveness of oral progestogen-only
preparations.
See appendix 1 of the BNF for a full list of drugs that are known to interact with oral
contraceptives.
Contact your Medicines Information Service (UKMI) for further advice if
needed.
Oral Contraception and EHC
April 2006
Medicines Information Skills for
NHS Direct Nurse Advisors & Health Information Advisors
Please list what background information you will require before answering an enquiry about
potential drug interactions with oral contraceptives.
Oral Contraception and EHC
April 2006