Oral Contraceptives and Vaginal Infections

Oral contraceptives do not cause bacterial vaginosis or vaginal yeast infections; in fact, they appear to reduce the risk of both conditions. 1

Bacterial Vaginosis

Oral contraceptives are protective against bacterial vaginosis, not causative. The most recent and highest quality evidence demonstrates:

Women using oral contraceptives have a 24-28% reduced risk of bacterial vaginosis compared to non-users (adjusted hazard ratio 0.72-0.76). 2, 3
The CDC's U.S. Medical Eligibility Criteria classifies vaginitis (including bacterial vaginosis) as Category 1 for combined hormonal contraceptives, meaning no restriction on use—there is no evidence that oral contraceptives cause or worsen bacterial vaginosis. 1
A large prospective study of 3,077 women over one year found oral contraceptive users had significantly decreased overall bacterial vaginosis prevalence (OR 0.76,95% CI 0.63-0.90). 2
The protective mechanism likely involves hormonal effects on cervical mucus and vaginal epithelium that create a less favorable environment for anaerobic bacterial overgrowth. 3

While oral contraceptives protect against bacterial vaginosis, older CDC guidelines note that women using oral contraceptives have an increased risk of cervical Chlamydia trachomatis infection, though they paradoxically have a lower risk of symptomatic pelvic inflammatory disease. 1
This creates a complex clinical picture where oral contraceptives may increase asymptomatic cervical infections while reducing upper genital tract complications. 1

Oral contraceptives reduce the risk of vaginal candidiasis rather than causing it. The evidence shows:

Oral contraceptive users have a 21-25% reduced risk of vaginal candidiasis (adjusted hazard ratio 0.75-0.79). 3
A prospective study of HIV-serodiscordant couples in Zambia found oral contraceptive pills were protective for candidiasis (aHR 0.79,95% CI 0.65-0.97). 3
Short-term studies (2 months) show minimal effects on vaginal flora, with only small decreases in H₂O₂-producing Lactobacillus species, which would theoretically increase candidiasis risk—yet this does not translate to clinical infections. 4

When counseling patients about oral contraceptives and vaginal infections:

Reassure patients that oral contraceptives will not increase their risk of bacterial vaginosis or yeast infections. 2, 3
If a patient develops bacterial vaginosis or candidiasis while on oral contraceptives, look for other risk factors: multiple sexual partners, vaginal douching (>5 times/week), high coital frequency (>5 times/week), BMI >25 kg/m², or history of prior infections. 5
The initial 6 weeks after starting oral contraceptives may show a transient increase in vaginal infection rates that improves over time, but this is still lower than non-users. 5
Do not discontinue oral contraceptives for recurrent bacterial vaginosis or candidiasis—the contraceptive method is protective, not causative. 2, 3

Depot medroxyprogesterone acetate (DMPA) is even more protective than oral contraceptives, reducing bacterial vaginosis risk by 28% (aHR 0.72), candidiasis by 25% (aHR 0.75), and trichomoniasis by 57% (aHR 0.43). 3
Intrauterine devices (IUDs) increase infection risk, with bacterial vaginosis rates of 11.7% in IUCD users versus 5.9% in oral contraceptive users and 2.9% in controls. 6