The potential for weight gain is another consideration when choosing a contraceptive for youth with obesity. The use of DMPA is associated with weight gain, and this weight gain is exacerbated for girls with obesity at the initiation of DMPA use. In a study of 450 adolescent girls aged 12–18 years, Bonny et al. demonstrated that adolescents with obesity who initiated DMPA were more likely (p < 0.001) to gain weight (mean weight gain of 9.4 kg) than adolescents with obesity who used either combined oral contraceptives (COCs) (0.2 kg) or no method (3.1 kg) [7]. They were also more likely to gain weight than adolescents who did not have obesity and initiated DMPA use. In contrast, there has been no associated demonstration of the use of estrogen-containing contraceptives and weight gain. A causal relationship between the use of these contraceptives and weight gain was not supported from the available evidence from a large systematic review of 49 trials evaluating the use of COCs or the patch [8].

The inherent effectiveness of some hormonal contraceptives may be diminished in obese adolescents. Higher metabolic rates, increased clearance of drugs metabolized in the liver, increased circulating blood volume, and higher drug sequestration in adipose tissue may result in decreased serum drug levels and inadequate contraceptive efficacy in obese adolescents [9]. Contraceptive failure rates with COC and the patch may be higher in adolescents with obesity; however, the failure rates are lower than those associated with barrier methods. While Westhoff et al. demonstrated that obese woman had lower maximum values of ethinyl estradiol than normal-weight women (85.7 vs. 129.5 pg/mL, p < 0.01), the lower concentration did not significantly impact follicular activity, and ovulation was still suppressed [10]. Dinger et al., however, found that among more than 55,000 US women, the COC failure rate was slightly higher in women with a BMI ≥ 35 kg/m² compared with women with BMI <35 (adjusted HR 1.5 (95% CI 1.3–1.8)) and risk of COC failure increases among overweight women as the COC estrogen dose decreases [11]. Studies evaluating the efficacy of the Ortho Evra contraceptive patch have included more overweight and obese women than other methods. A 2002 multicentered, open-labeled study found that contraceptive failure may have been increased among obese women weighing more than 90 kg [12]. Small studies evaluating the effectiveness of the estrogen-progestin pill, patch, or vaginal ring have demonstrated no differences in contraceptive failure for these methods in overweight or obese women relative to normal-weight women with therapeutic hormone levels and adequate suppression of follicular development in obese women using the ring [12, 13].

The intrauterine device (IUD), contraceptive implant, and DMPA are all effective methods of contraception for adolescents with obesity. A copper- or levonorgestrel-releasing IUD is the best contraceptive option for obese adolescents. The Contraceptive CHOICE Project, a large prospective cohort study including thousands of women, with 27% and 35% of subjects meeting criteria for overweight and obesity, respectively, demonstrated overall failure rates of less than 1 pregnancy per 100 woman-years regardless of BMI [14]. The implant has also been found to be highly effective in obese women. Mornar et al. demonstrated that while obese women with the implant had lower concentration of plasma hormones compared to their nonobese counterparts, these differences did not reach statistical significance and there were no pregnancies in women who weighed ≥70 kg [15]. Despite its association with weight gain, DMPA has been shown to be an effective contraceptive method for obese women with no pregnancies documented in over 16,000 woman-cycles of DMPA use [16].