Combined hormonal contraceptives and migraine: An update on the evidence

HOW ESTROGEN AFFECTS MIGRAINE

Of note, migraine can be exacerbated during times of cycle irregularity, such as adolescence and perimenopause, the 2 times during a woman’s life associated with the highest risk of unintended pregnancy.^10,11

STROKE RISK: ESTROGEN DOSE MATTERS

Shortly after the first combined oral contraceptives were released, reports of adverse events began to appear, although serious events were relatively rare. In response, prescribing guidelines advised against giving oral contraceptives to women with a history of deep vein thrombosis, myocardial infarction, stroke, or hypertension. Also, over the years, the hormonal content of the formulations was successively reduced, and with each reduction in estrogen, a decrease was observed in venous thrombosis and pulmonary embolism.^12,13 Current low-dose formulations are considerably safer than high-dose options but are not entirely without risk.¹⁴

Stroke risk with combined oral contraceptives was first highlighted in a landmark article in 1975.¹⁵ However, the authors were unable to correlate the risk with the estrogen concentration of the pill, since 23 of the 25 women who suffered thrombotic stroke while taking the mestranol-containing formulation took 100-μg pills, and all 20 women who had strokes while taking the ethinyl estradiol formulation took 50-μg pills. Thus, by today’s standards, they were all taking high-dose pills. The risk of thrombotic stroke was 4 to 5 times higher in users than in nonusers.

In 1996, a study from the World Health Organization¹⁶ reported an increased risk of stroke with high-dose combined oral contraceptives (odds ratio [OR] 5.30, 95% confidence interval [CI] 2.56–11.0). With preparations containing less than 50 μg of ethinyl estradiol, the risk was not statistically significant (OR 1.53, 95% CI 0.71–3.31). These numbers were for Europe only; in developing countries, the risk was elevated regardless of dose, presumably due to additional risk factors in combined oral contraceptive users. The majority of strokes were in smokers taking 50-μg pills, with an average age greater than 35.

In 2002, a 5-year case-control study in Denmark found that the risk of stroke with combined oral contraceptives correlated directly with the estrogen content, from no increased risk with the newest and lowest-dose formulation (containing ethinyl estradiol 20 µg) to an OR of 4.5 with the older high-dose (50 µg) formulations.¹⁷

Reassuringly, a 2012 retrospective review of the Danish national registry¹³ revealed a low absolute risk of arterial events in users of combined oral contraceptives: 21.4 per 100,000 person-years for thrombotic stroke, and 10.1 per 100,000 person-years for myocardial infarction. Further, these risks were substantially lower with 20-μg ethinyl estradiol products than with those containing 30 to 40 μg.¹³ An important limitation of this large database review is that it did not control for important stroke risk factors such as obesity and smoking.

Although international studies^14,16 continue to show a small but increased risk, more than 30 years have passed since a US study found an increased risk of stroke with combined oral contraceptives.

The discrepancy between US and international studies is possibly explained by the strong relative contraindication in the United States to the use of combined oral contraceptives in smokers over the age of 35 and the more prevalent use of high-dose pills in international studies. High-dose pills had been used in most of the stroke cases in the 1996 World Health Organization study¹⁶ but were used by only 0.7% of the women in the case and control groups in 2 pooled US studies from the same time period.¹⁸ Similarly, in these US studies, only 17% of the women were smokers on combined oral contraceptives, whereas in the international study, 51% of the women who had strokes and 38% of those in the control groups were smokers.

A large US study¹⁹ reviewing 3.6 million woman-years of use found no increased stroke risk (OR 0.96) in current users of low-dose combined oral contraceptives, results similar to those of a pooled analysis of US studies.¹⁸ Though this pooled analysis showed an adjusted increased risk of ischemic stroke in women reporting a history of migraine (OR 2.08, 95% CI 1.19–3.65), these conclusions were based on only 4 cases. The prevalence of migraine was identical in women who did or did not have strokes, 7.8% vs 7.7%, respectively, but the risk was judged to be increased after adjusting for other factors. But one important factor was not adjusted for: only 11 of the 1,017 women in the case and control groups were using 50-μg ethinyl estradiol pills, and 4 of the strokes were in this group of 11 women.

STROKE RISK INCREASES WITH FREQUENCY OF MIGRAINE AURA

Use of combined hormonal contraceptives in women who have migraine with aura remains controversial, based on good evidence that aura increases stroke risk²⁰ and good evidence that high-dose oral contraceptives increase stroke risk.¹⁵

A cohort study encompassing more than 470,000 person-years with a median follow-up of 26 years found that while migraine without aura conferred no increase in risk of all-cause mortality, migraine with aura did.²¹

The longitudinal Women’s Health Study analyzed data from 27,798 women over age 45 and found that migraine with aura conferred an increased risk of cardiovascular disease (including stroke) that varied directly with aura frequency.²² Aura frequency less than once a month conferred a risk 2 times higher than in women without migraine, and the risk was more than 4 times higher when aura frequency exceeded once a week.

Similarly, an analysis of the World Health Organization study of stroke in young women found that the adjusted risk of ischemic stroke was significantly and directly associated with aura frequency.²⁰

Potential explanations for this increased risk with greater aura frequency include changes induced during spreading cortical depression, shared genetic predispositions, and common underlying comorbidities such as patent foramen ovale.^23–26

Though studies have shown that combined oral contraceptives in continuous regimens²⁷ or in regimens that minimize drops in estrogen levels²⁸ can help improve general headache and menstrual-related migraine, these studies have excluded patients who have migraine with aura.

In a pilot study,²⁹ 28 women referred to a tertiary headache clinic who had migraine with aura and intractable menstrual-related migraine were offered combined hormonal contraception in the form of a vaginal ring that releases only 15 μg ethinyl estradiol per 24 hours, thereby reducing peak estrogen exposure to a level lower than those encountered with the native menstrual cycle (with the suppression of ovulation). The women used this continuous ultra-low-dose hormonal contraception without placebo days. After a mean follow-up of 8 months, this regimen reduced aura frequency from a baseline average of 3.2 per month to only 0.2 per month. No woman had an increase in aura frequency, and menstrual-related migraine was eliminated in 21 (91.3%) of the 23 evaluable patients.

CHOOSING THE OPTIMAL CONTRACEPTIVE FORMULATION

Today, ultra-low-dose combined oral contraceptives (containing 10–15 µg of ethinyl estradiol) inhibit ovulation with doses of estrogen that are in a midphysiologic range. Consequently, they expose women to lower peak concentrations of estrogen than they would experience in their natural menstrual cycle (Figure 1). If a combined oral contraceptive is used in women with migraine with aura, lower estrogen doses (≤ 20 µg ethinyl estradiol) are preferred to decrease aura frequency and minimize the risk of stroke associated with high-dose ethinyl estradiol formulations.

Does the progestin matter?

Though there has been debate about whether different types of progestins alter the risk of venous thromboembolism,^30,31 the chosen progestin does not seem to affect arterial risks such as stroke and myocardial infarction.¹⁴

All current guidelines note that progestin-only pills can be safely offered to women with migraine with aura. However, progestin-only pills have a shorter half-life than combined hormonal contraceptives and must be taken consistently and on time to ensure contraceptive efficacy and minimize abnormal bleeding. Patients who cannot adhere to a strict daily pill regimen may increase their risk of unintended pregnancy. In addition, progestin-only pills do not help with reducing episodes of migraine because they prevent ovulation only about half of the time.² In contrast, a progestin-only arm implant is not only considered safe to use in women with migraine with aura, it may also prevent ovulation more reliably. Though progestin arm implants have the potential to reduce menstrual migraine and aura, this requires further study to confirm.

For menstrual-related migraine

In clinical practice, providers may offer certain combined hormonal contraceptives to women with debilitating menstrual-related migraine to prevent attacks. Although menstrual-related migraine rarely if ever is accompanied by aura, these patients may still have migraine with aura at other times of the month.

In women with menstrual-related migraine, any decrease in estrogen level greater than 10 µg of ethinyl estradiol may trigger an estrogen-withdrawal migraine. All currently available regimens of combined hormonal contraceptives that follow a 21-days-on, 7-days-off plan entail a drop in ethinyl estradiol of more than 10 µg (Figure 1).