Levonorgestrel in Combined Oral Contraceptives: How It Works and What You Need to Know

When you pick up a pack of birth control pills, you might not think about the specific hormones inside. But if you’re trying to understand how your pill works - or why you’re experiencing side effects - one name keeps showing up: levonorgestrel. It’s the most common progestin used in combined oral contraceptives today, and it plays a critical role in preventing pregnancy. But what exactly is it? How does it work? And is it right for you?

What is levonorgestrel?

Levonorgestrel is a synthetic hormone designed to mimic progesterone, one of the body’s natural female sex hormones. It’s not found in nature - it’s made in a lab. Since the 1970s, it’s been the go-to progestin in birth control pills because it’s stable, effective, and well-tolerated by most people. In combined oral contraceptives, it’s paired with estrogen, usually ethinyl estradiol. Together, they stop ovulation, thicken cervical mucus, and thin the uterine lining - three ways to prevent pregnancy.

Unlike older progestins like norethindrone, levonorgestrel has a stronger effect on the cervix and endometrium, which makes it more reliable at blocking sperm and preventing implantation. It’s also used in emergency contraception (like Plan B), but that’s a much higher dose than what’s found in daily pills.

How does levonorgestrel prevent pregnancy?

It’s not just one trick - levonorgestrel works in three ways at once.

1. Stops ovulation. In most cycles, the pill suppresses the signal from your brain that tells your ovaries to release an egg. Without an egg, pregnancy can’t happen.
2. Thickens cervical mucus. Normally, cervical mucus becomes thin and slippery around ovulation to help sperm swim through. Levonorgestrel makes it thick and sticky - like glue - so sperm can’t get past.
3. Thins the uterine lining. If an egg somehow gets fertilized, a thin lining makes it harder for it to attach and grow. This isn’t the main way the pill works, but it adds another layer of protection.

Studies show that when taken perfectly - every day at the same time - combined pills with levonorgestrel are over 99% effective. In real life, with missed pills or delays, effectiveness drops to about 93%. That’s still better than condoms, but consistency matters.

What are the common side effects?

Most people tolerate levonorgestrel well, but side effects are common, especially in the first few months. Your body is adjusting to a new hormone balance.

• Spotting or lighter periods - this is normal. Many users stop getting periods altogether after a few months.
• Breast tenderness - usually fades after 2-3 cycles.
• Nausea - often goes away if you take the pill with food or at bedtime.
• Mood changes - some report increased irritability or low mood. If it’s severe or lasts more than 3 months, talk to your doctor.
• Headaches - can be mild or worsen existing migraines. If you get migraines with aura, levonorgestrel pills aren’t recommended.

These side effects don’t mean the pill isn’t working - they just mean your body is adapting. Most settle down by cycle three. If they’re unbearable or get worse, it’s not about being “weak” - it’s about finding the right formula for your body.

Who should avoid levonorgestrel pills?

Not everyone can safely use combined hormonal contraception. Certain health conditions make it risky.

• History of blood clots, stroke, or heart attack
• Uncontrolled high blood pressure
• Severe liver disease
• Breast cancer or history of estrogen-sensitive cancers
• Migraines with aura (especially after age 35)
• Smoking and over 35 years old - this combination significantly raises clot risk

If any of these apply to you, your doctor may recommend a progestin-only pill (like the mini-pill), an IUD, or another method. Levonorgestrel isn’t dangerous for everyone - but it’s not safe for everyone either.

How does levonorgestrel compare to other progestins?

There are dozens of progestins used in birth control. Levonorgestrel is just one. Here’s how it stacks up against others you might see on your prescription.

Levonorgestrel has moderate androgenic activity - meaning it can slightly increase male hormone effects. That’s why some people notice more acne or hair growth. If you struggle with acne or hirsutism, your doctor might switch you to drospirenone or desogestrel, which have less of this effect. But if you’re not having those issues, levonorgestrel is just as effective and often cheaper.

Does levonorgestrel affect long-term fertility?

No. Once you stop taking the pill, your body returns to its natural cycle. Most people ovulate again within 1-3 months. Studies tracking women who stopped combined pills found no delay in conception compared to those who used non-hormonal methods. There’s no evidence levonorgestrel causes permanent infertility.

Some people think their body “forgot” how to ovulate after years on the pill. That’s not true. If you don’t get pregnant right away, it’s likely due to other factors - age, timing, or underlying conditions like PCOS - not the pill.

What if I miss a pill?

Missing one pill is common. What you do next matters.

• If you miss one pill anywhere in the pack: Take it as soon as you remember, even if that means taking two pills in one day. You’re still protected.
• If you miss two or more pills in the first two weeks: Take the most recent missed pill, skip the others, and continue. Use backup contraception (like condoms) for the next 7 days.
• If you miss pills in the third week: Skip the placebo week, start a new pack immediately. No break. This avoids ovulation.

Levonorgestrel has a half-life of about 24-30 hours, so missing a pill by more than 12 hours reduces protection. That’s why consistency is key. Setting a daily alarm or linking pill-taking to brushing your teeth helps.

Is levonorgestrel right for you?

There’s no single “best” birth control pill. What works for your friend might not work for you. But levonorgestrel is a solid choice if:

• You want a reliable, well-researched option
• You don’t have contraindications like blood clots or migraines with aura
• You’re okay with possible mild side effects in the first few months
• You can take it at the same time every day

If you have acne, mood swings, or weight concerns, talk to your doctor about switching progestins. But don’t assume levonorgestrel is the problem - sometimes it’s the estrogen dose, or your body just needs time.

Many people stay on levonorgestrel pills for years - even decades - without issues. Others switch after a year. Both are normal. The goal isn’t to find the perfect pill forever. It’s to find one that works now, and be ready to change if things shift.

What’s next if levonorgestrel isn’t working?

If side effects persist, or you’re not happy with your pill, you’re not stuck. There are other options:

• Try a different estrogen dose - lower (20 mcg) or higher (30-35 mcg) - to balance side effects
• Switch to a progestin with less androgenic activity (like drospirenone or desogestrel)
• Consider a progestin-only pill or hormonal IUD (like Mirena or Kyleena), which deliver levonorgestrel directly to the uterus with less systemic effect
• Explore non-hormonal options like the copper IUD or condoms

Don’t suffer in silence. Birth control should empower you - not make you feel worse. Your body, your choice, your doctor’s job is to help you find the match.