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Why are there so many different types of oral contraceptives? – The Estrogen Equation

Posted Jun 09 2010 6:12pm

Well, if you’ve read my previous post (which I’m sure you did!) you already know that the two main components of combined OCP’s are estrogen and progesterone.  What makes each type of pill distinct is the way in which these two components are dosed and formulated.  In this post, let’s discuss only the estrogen component.  We can talk about the progesterone later.

Combination OCP’s can be described as low-dose, medium-dose or (rarely) high-dose.  This refers to the dose of estrogen in the tablet.  A low-dose pill usually contains 20 micrograms of estrogen.  Medium dose pills contain between 30 and 35 micrograms.  Higher doses can go up to 50 micrograms.   

Why does it matter?  Well, a low-dose pill is great for somebody who needs the pill for pregnancy prevention, but doesn’t require the higher doses needed to suppress other conditions (like endometriosis or excessive menstrual bleeding).  A low dose of estrogen also minimizes the risk of complications from oral contraceptives (such as an increased risk of blood clots and other potentially life-threatening medical conditions). 

So, why wouldn’t everyone choose to take a low-dose pill?  Some women taking low-dose pills may not have bleeding during the week of placebos (inactive pills) because the low dose of estrogen keeps the lining of the uterus (womb) very thin.  Therefore, little tissue is shed (as menstrual flow) when the body withdraws from the estrogen.  Amenorrhea (absence of a period) can be normal and healthy in this situation and is not a cause for concern in the absence of other symptoms. 

In some women, bleeding between periods (metrorrhagia) may occur when the dose of estrogen is too low to stabilize the lining of the uterus between cycles.  If this occurs, it doesn’t mean the pill isn’t protecting you against pregnancy.  It just means you may need to switch to a different pill in order to reduce inconvenient or unpredictable bleeding

Spotting or mid-cycle bleeding can also be more likely to occur on a low-dose pill if doses are missed or are taken late.  Therefore a low-dose pill may be a poor option for women who can’t manage to take their pill on time every day.  Obviously, back-up contraception (a condom, perhaps?) should be used when necessary.

Oral contraceptives with 30 to 35 micrograms of estrogen may be a better choice for women who need to suppress their menstrual cycles because of endometriosis, pelvic pain, excessive menstrual bleeding (menorrhagia), or who have had irregular bleeding on lower dose oral contraceptives. 

If they dose of estrogen is the same in every pill, the type of pill can be called “monophasic.”  Some oral contraceptives have a dose of estrogen which varies from the first to the third week (triphasic).  These pills are meant to mimic the natural variation in hormones that occurs during a normal menstrual cycle.  Whether a monophasic or a triphasic pill is right for you will depend on a number of factors which you may wish to discuss with your gynecologist.


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