DMPA (you may know this as Depo Provera) is associated with 10-15 pounds of weight gain over 3 to 5 years. Not all women will experience this and some women will lose weight on DMPA. If a woman gains 5% or more of her body weight over the first 6 months of treatment with the DMPA she has the greatest risk of gaining more weight and should be counseled on weight loss or select another method.
Weight issues can affect the hormonal levels in turn.When the blood level of your contraceptive hormones change, the effect in a woman can be that she sees change in both her symptoms and even effectiveness of her pills. If levels of your hormonal contraception dip low, escape ovulation can occur. This is how the production of estrogen, progesterone and testosterone from the ovaries can alter,and patients can then develop bleeding or other undesirable side effects, such as pregnancy. The levels have been known to change secondary to medications such as antibiotics or other medicines, and some foods could cause issues. At the time of vomiting or other minor illnesses, you may not actually get the full dosage of medicine absorbed. It's an important subject to discuss with your gyno.
Women who are extremely overweight present other challenges to hormonal contraception. Not only because many methods have not properly studied large groups of large patients, but the obese patient also has greater blood volume in which the hormones in contraceptive methods is distributed. This in effect will decrease their blood level and could put them at greater jeopardy of getting an unplanned pregnancy. When obese patients have surgery, the changes in how they absorb food and medication, as well rapid weight transition can put a woman at greater risk of hormonal level fluctuations from her contraception. Since 1/3 American women are obese, this subject of how they fair on hormonal contraception, is a common cause for concern among gynos. We have discussed the option of using the NuvaRing contraception or the patch both of which should have a more consistent blood level, rather than the oral contraceptive pill which might not be absorbed as well in the patient who has been banded or whom has had gastric banding. Even the American Congress of Obstetricians and Gynecologists stated that there "patients who have had bariatric surgery should consider non-hormonal methods" such as IUD or barrier methods of contraception. So there are choices, but we will have to see what direction some of the studies go.
In a recent editorial in Contraception by Zaher Merhi from the University of Vermont College of Medicine, it is pointed out that studies of blood levels need to be done, especially for the popular method of IUD with the hormone levonorgesterel: Mirena, Liletta and Skyla. Until these studies are done, you need to work closely with your gyno as your weight changes so that you can be protected from pregnancy when you aren't prepared, and prepared the best when you are ready for pregnancy. And then once pregnant if you have had weight loss or bariatric surgery there are other nutritional considerations.