What are the uncommon side effects of birth control pills?

Uncommon Side Effects of Birth Control Pills

The most concerning uncommon side effects of birth control pills are thromboembolic events, including venous thromboembolism, myocardial infarction, and ischemic stroke, which occur at rates of approximately 6 per 10,000 person-years for combined oral contraceptives compared to 2 per 10,000 person-years in non-users. 1, 2

Cardiovascular Side Effects

Thromboembolic Events

• Venous thromboembolism (VTE): Risk increases from 1-2 per 10,000 woman-years in non-users to 3-9 per 10,000 woman-years in COC users 3, 2
• Myocardial infarction: 1.6-fold increased risk compared to non-users 2
• Ischemic stroke: 1.7-fold increased risk compared to non-users 2, 4

Risk factors that further increase these risks include:

• Age over 35 years
• Smoking
• Hypertension
• Obesity
• Migraine with aura
• Dyslipidemia 1, 5

Blood Pressure Effects

• Hypertension can develop in some users, particularly with combined hormonal contraceptives containing ethinyl estradiol 1
• Drospirenone-containing pills may actually decrease blood pressure due to anti-mineralocorticoid effects 1

Metabolic and Endocrine Side Effects

• Hyperkalemia: Rare with drospirenone-containing pills, primarily in women with risk factors for hyperkalemia 1
• Glucose intolerance: Uncommon but may occur, especially in women with pre-existing diabetes 1
• Liver tumors: Rare benign hepatic adenomas or very rare hepatocellular carcinomas 3

Neurological and Psychiatric Side Effects

• Depression and mood changes: Occur in approximately 2.2% of users 3
• Decreased libido: Reported in about 2.8% of users, particularly in PMDD studies 3
• Migraine exacerbation: Particularly concerning if accompanied by aura 1

Other Uncommon Side Effects

• Chloasma (skin hyperpigmentation): More common in women with history of chloasma gravidarum 3
• Contact lens intolerance: Problems with contact lens wear can develop 3
• Gallbladder disease: Increased risk of symptomatic gallbladder disease 3
• Angioedema exacerbation: In women with hereditary angioedema 3

Differences Between Combined and Progestin-Only Pills

Progestin-only pills (POPs) have a more favorable side effect profile for certain uncommon adverse effects:

• No increased risk of thromboembolism: Unlike combined pills, POPs are not associated with increased risk of blood clots 6, 7
• No effect on blood pressure: POPs do not typically raise blood pressure 1
• Suitable for women with contraindications to estrogen: Including those with history of VTE, migraine with aura, or certain cardiovascular risk factors 1, 7

Monitoring and Management

For women taking combined oral contraceptives:

• Monitor blood pressure periodically
• Be alert for warning signs of serious complications (severe headache, chest pain, severe leg pain, shortness of breath, vision changes) 3
• Consider switching to progestin-only methods if concerning side effects develop 1

Important Caveats

1. The absolute risk of serious side effects is low in young, healthy women without additional risk factors
2. The risk of venous thromboembolism is actually higher during pregnancy than with COC use 1
3. COCs are associated with reduced risk of ovarian, endometrial, and colorectal cancers, providing a net decrease in cancer risk for most women 1
4. Irregular bleeding patterns are common with both combined and progestin-only methods but are generally not harmful 1

When counseling patients about birth control options, it's important to weigh these uncommon risks against the significant benefits of effective contraception and the potential non-contraceptive benefits that hormonal methods can provide.