Side Effects of Oral Contraceptives
The most serious adverse event associated with oral contraceptive use is the increased risk of blood clots (venous thromboembolism), which increases from 1 per 10,000 to 3-4 per 10,000 woman-years during combined oral contraceptive use. 1
Common Side Effects
Transient Side Effects
- Irregular bleeding (breakthrough bleeding or spotting)
- Headache
- Nausea
- Breast tenderness
- Mood changes 1, 2
These side effects are typically transient and often resolve within 3-5 months of continued use 3.
Cardiovascular Risks
Venous Thromboembolism (VTE)
- Risk increases from approximately 2 per 10,000 person-years in non-users to 6 per 10,000 person-years in users 4
- Risk factors that further increase VTE risk:
- Age over 35 years
- Smoking
- Obesity
- Prolonged immobilization
- Family history of VTE
- Thrombogenic mutations 5
Arterial Thrombotic Events
- Increased risk of myocardial infarction and stroke
- Risk is primarily in women with other risk factors:
- Smoking (particularly ≥15 cigarettes daily)
- Age ≥35 years
- Hypertension
- Hypercholesterolemia
- Diabetes 5
Blood Pressure Effects
- Some women experience increased blood pressure while taking combined oral contraceptives
- The Nurses' Health Study found users had a significantly increased relative risk (1.8) of hypertension compared with never-users 1
- Blood pressure typically returns to pretreatment levels within 3 months of discontinuation 1
Absolute Contraindications to Combined Oral Contraceptives
Combined oral contraceptives should not be prescribed for patients with:
- Severe and uncontrolled hypertension (systolic ≥160 mmHg or diastolic ≥100 mmHg)
- Ongoing hepatic dysfunction
- Complicated valvular heart disease
- Migraines with aura or focal neurologic symptoms
- History of thromboembolism or thrombophilia
- Complications of diabetes (nephropathy, retinopathy, neuropathy, other vascular disease)
- Complicated solid organ transplantation
- Current breast cancer
- Age ≥35 years and smoking ≥15 cigarettes daily
- ≤21 days postpartum 1
Cancer Risks and Benefits
- Reduced risk: Endometrial, ovarian, and colorectal cancers 1, 4
- Small increases in risk: Breast and cervical cancers 1
- Overall neutral balance between cancer risks and benefits in past users after long-term follow-up 1, 4
Progestin-Only Pills (POPs)
POPs have a more favorable side effect profile for certain adverse effects:
- No increased risk of thromboembolism
- No effect on blood pressure
- Suitable for women with contraindications to estrogen 4
Monitoring and Management
Before Initiation
- Blood pressure measurement
- Comprehensive medical history to identify contraindications
- No pelvic or breast examination required prior to initiation 1
Follow-up
- Routine follow-up visit 1-3 months after initiating combined oral contraceptives to address adverse effects or adherence issues 1
- Regular blood pressure monitoring throughout contraceptive therapy 1
Managing Common Side Effects
- Breakthrough bleeding: Usually resolves within 3 months; if persistent beyond this time, consider evaluation for other causes 3
- Nausea: Consider switching to a lower estrogen dose (20 μg ethinyl estradiol) if persistent 2
- Headaches: Switching preparations sometimes helps; for headaches during pill-free interval, consider extended cycle regimen 2
- Mood changes: Relationship to oral contraceptive use is difficult to assess; consider alternative methods if severe 2
Important Considerations
- For women with risk factors for cardiovascular events, progestin-only methods are safer alternatives 4
- Most broad-spectrum antibiotics (except rifampin) do not affect the contraceptive effectiveness of combined oral contraceptives 1
- The risk of VTE during pregnancy (10-20 per 10,000 woman-years) is actually higher than the risk with oral contraceptive use 1
- Smoking cessation should be strongly encouraged in all oral contraceptive users, particularly those over 35 5
Remember that patient education about potential side effects before initiation can improve continuation rates and decrease the chance of unanticipated adverse effects.