Question about Depo Provera ?

Nurses General Nursing


Ok I have a question concerning Depo Provera (medroxyprogesterone acetate).

My question is - How does Depo Provera work to maintain Birth control for the 3-month period?

Ok - Let me go more into detail..... I understand that the patient receives the shot (150mg) q 3 months and that the mechanism of action is exerted by preventing the females egg cells from ripening. If an egg is not released from the ovaries during the menstrual cycle, it cannot become fertilized by sperm and result in pregnancy. Depo Provera also causes changes in the lining of the uterus that make it less likely for pregnancy to occur. The reason that the periods stops is because Depo Provera causes a resting state in the ovaries by inhibiting the secretion of gonadotropins which, in turn, prevents follicular maturation and ovulation and results in endometrial thinning. These actions produce its contraceptive effect.. When the ovaries do not release an egg monthly, the regular monthly growth of the lining of the uterus does not occur and, therefore, the bleeding that comes with the normal menstruation does not take place. When the female stops using the Depo Provera the menstrual period will usually, in time, return to its normal cycle.

Radioimmunoassay procedure for the assay of medroxy-progesterone acetate in serum, the apparent half-life for medroxy progesterone acetate following IM administration of Depo Provera is approximately 50 days. Therefore, if the half-life of the Depo Provera is 50 days why wouldn't the female not need the shot q 2months?

If my understanding of half-life is correct then at the 50-day mark there would be 75mg of Depo Provera still active. Would this still be an effective therapeutic level?

I understand that when Test injections are given for HRT that the length of carbon chains has a direct impact on half life (longer the carbon chain on C19 the longer the half life) (half life of Test is between 1 to 10 days--depending on ester chain) but this is not the situation with Depo Provera.

Can someone please clarify my thinking?


1,049 Posts

Specializes in midwifery, ophthalmics, general practice.

I think you ask too many questions!!!!!!!!!!!!!! ok I give this stuff all the time - will see if I can find an answer!!



1,037 Posts

We had a lady who had been on it for 5yrs, taking like she is suppose to... Just found out she is 21weeks pregnant ..


3,778 Posts

Specializes in Trauma,ER,CCU/OHU/Nsg Ed/Nsg Research.

That happened to me. I got pregnant after my second shot. I also bled for the first 6 weeks after my first dose.


3,778 Posts

Specializes in Trauma,ER,CCU/OHU/Nsg Ed/Nsg Research.

I was about 20 weeks when I found out, too. The GYN told me that it was fairly normal to stop menstruating after the 2nd dose, and that my weight gain could be normal, too. I took a preg. test on my own, for peace of mind, and viola- it was positive.

canoehead, BSN, RN

6,856 Posts

Specializes in ER.

The half life indicates how long it takes for half the drug to be metabolized. Apparently it's supposed to be effective even when smaller amounts than half are in your bloodstream.

One thing I don't get is that many women need varying strengths of the pill but there is only one strength for Depo as far as I know. Perhaps that would account for a lot of the sensitivities and pregnancies that we keep hearing about.


144 Posts

I have been on the depo for 5 years now. I love it!

I just hope down the road I do not end up getting pregnant! I would love to have a little girl running around, but I do not think I would like to bring a child in the world as it is now. Too much violence and whatnots.


754 Posts

Specializes in Everything but psych!.

I heard that they were considering revising their guidelines for Depo, which would exclude women over 170 lb as candidates for the medication.


6 Posts

Originally posted by Audreyfay

I heard that they were considering revising their guidelines for Depo, which would exclude women over 170 lb as candidates for the medication.


Do you know why the revision ? Does it have to do with BW and the effective dose ?

Sarah Kat

229 Posts

I know this is an old thread, but I am ressurecting it because I just got my first depo shot today. I saw that a few previous replies talk about getting pregnant on the shot. I am over 170 lbs :o and I don't want to get pregnant. The nurse who administered the shot said to use backup for two weeks. For the women who got pregnant, did you follow the guidelines? Are you over 170 lbs? Anyone hear any more on this?


263 Posts

Speak of the devil! A good nurse friend of mine just discovered she was about 2 months pregnant about a week ago, and using depo. She is very concerned that this might cause birth defects or low birth weight. Any input? I know absolutely nothing about OB/GYN stuff. :eek: She's extremely stressed out about this. Not only an unexpected pregnancy but also a potentially risky one? She's 39 years old AND diabetic (controlled by diet).



408 Posts

I too had that one unpleasant side effect, I named her andrea,lol,

the manufactures-sp guidlines state that there is a poss. of congenital defects but does not specify what kind my daughter was born at 35 wks EGA and had ventricular septal defect, patent ductus arterious, congeital hip displasia, and occult spina bifida. I also had several other risks fam hx, drinking during first trimester, recent MMR{had it , the depo,the flushot,tetanus, and my tb test the same day}, poor nutrition, and serious stress. so I,m not sure if the congenital anomalies are connected to the depo or the combo.

As for me I had been on depo for 18 mos. was 110 lbs and current on my shots

everything has a failure rate-except abstinance, and what fun would that be.:D

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