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Contraceptive Injection

There are essentially two different forms of contraceptive injection, also called “delivery systems”; there is a shorter term type and the longer term type. The first type is Depot Provera (= chemically DMPA or Depot medroxy- progesterone acetate). 150 mg of this is injected every three months deep into the buttock muscle. There will likely be another monthly injection form available in the future (Ref. 15, p.333). Here is a more detailed description (thanks to for this link) of this method as well as the side-effects.

The second delivery form is called Norplant, a subdermal contraceptive implant system of crystalline levonorgestrel. This lasts for 5 years and has a success rate for contraception of 98.7%, which is comparable to tubal ligation. Side effects for DMPA are possible light calcium loss in the bones, which can be counteracted through calcium intake. Cervical and ovarian cancer risk is unaffected, but uterine cancer risk is significantly reduced. The risk for breast cancer is about the same as for the regular BCP (1.6 to 1.8-fold higher). This method was withdrawn by the FDA, because of too many side-effects and many law suits, see details here (thanks to for this link).

There can be episodes of irregular spotting and bleeding for the first few weeks with DMPA, but subsequently there is often a long stretch of no periods.

With the subdermal contraceptive implant system headaches, mood swings,weight gain and irregular spotting for a period of time are the most common side effects. No cancer cases are reported with Norplant. Return of fertility comes within days of a few weeks after removal of the subdermal system as progesterone levels get flushed out quickly. However, with DMPA fertility may take up to 1 or 2 years to recover as it takes that long for normal ovulation to return.

Both injectable type contraceptive methods have one down fall: certain medications can accelerate the breakdown of the hormones by influencing the liver metabolism. The table below (modified from Ref. 15, p. 332) lists some of the more common medications known to interfere with the liver metabolism thus lowering estrogen levels and the effectiveness of the BCP.

Birth Control Ethics And Church Groups

Certain churches are opposed to the BCP because it is perceived as an interference into the natural hormone balance of a woman’s body.

I respect this point of view. There is a body of literature surrounding hormone replacement in menopause that also questions whether every woman needs replacement and in 2001 there was a consensus that only a certain proportion likely needs hormone replacement ( Ref.17).

Since then various publications appeared in 2004 and 2005 suggesting that there are inherent risks in estrogen administration leading to a small, but measurable risk of heart attacks and strokes. Ask your physician for a frank discussion about these matters. Discuss these things with your partner and with your minister, priest or religious leader. Some women have extremely irregular periods and heavy periods and these women are allowed contraception by the Catholic Church. The contraceptive effect in this case is considered a side effect. The main use of the contraceptive pills is to regulate the periods. Again, discuss this with the priest.

Medications that may reduce effectiveness of BCP, injectable or implantable birth control methods
Name of medication: Comments:
carbamazepine (=Tegretol) used as anti-seizure, anti-migraine, and anti-manic medication
topiramate (=Topamax) used as antiepileptic and by some physicians for weight loss
felbamate (=Felbatol) antiepileptic medication, which can lead to aplastic anemia and to liver failure
phenytoin (=Dilantin) old established antiepileptic medication
rifampin (=Rifamate, Rifadin) antituberculous medication and DNA dependent RNA polymerase inhibitor
primidone (=Mysoline) antiepileptic medication
phenobarbital (= a barbiturate) antiepileptic and sleeping pill

Ask your physicians, if you are on any of these medications and you are contemplating the BCP. You likely should use another contraceptive method or consider changing medications with the help of your treating physician.



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Last modified: August 15, 2014

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.