The Differences Between Monophasic vs. Biphasic Pills

How Does Combination Birth Control Work?

Combination birth control pills, also known as ‘the pill’, work by introducing synthetic forms of estrogen (ethinyl estradiol) and progesterone (progestin) to your body. These hormones have several effects on the menstrual cycle:

• Suppression of Ovulation: The hormones in birth control pills prevent ovulation by inhibiting the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Without ovulation, there is no egg available for fertilization.
• Thinning of the Endometrium (lining of the uterus): Birth control pills can lead to a thinner uterine lining, reducing the chances of implantation if fertilization occurs.
• Alteration of Cervical Mucus: The hormones makes cervical mucus thicker and more difficult for sperm to penetrate the cervix and reach the egg.

Monophasic vs Biphasic Pills

Monophasic and biphasic birth control pills are two types of combination oral contraceptives (COCs) that contain both estrogen and progestin. The primary difference between them lies in the hormonal composition and dosing regimen.

Monophasic pills have a consistent dosage of estrogen and progestin throughout the entire pill pack. All the active pills contain the same level of hormones. These pills are taken daily for a predetermined period, usually 21 days, followed by a week of inactive (placebo) pills.

Biphasic pills, as the name suggests, have two different hormone dose combinations within a single pill pack. The hormone levels change once during the cycle, usually after the first 10 days. The amount of estrogen stays the same, but the level of progestin is increased in the next 10–14 days. The last seven days (if included) are placebo pills and do not contain hormones.

The thought with biphasic birth control, is that it more closely mimics the rise and fall of hormones as in the “natural” menstrual cycle. However, both options are equally effective in preventing pregnancy, and have their own pros and cons.

Comparing Length of Cycle

Monophasic

Most monophasic birth control pills come in packs with 21–24 active pills. It is essential to be aware of how many active pills are in your pack (they are often a different colour). If you wish to extend your cycle past the typical one month, you can skip the hormone free interval (4–7 days depending on the pill) and go right back into a new package of active pills.

The convenience of monophasic pills is that you can choose how long your cycle is, to an extent. You can do one, two, three, or even longer cycles—and it will not change the effectiveness of the pills. Some people do find that they experience spotting when they extend their cycle more than two or three months.

Biphasic

Biphasic pills are different in that they come in two possible forms: “regular” and extended cycle. The “regular” cycle is 28 days. It is essential to take the hormone containing in the right order and within the right sequence. It is also important to take the inactive pills when directed. You cannot skip the hormone-free interval with “regular” biphasic birth control pills.

If you wish to lengthen your cycle with biphasic birth control, the only option is the extended cycle type. These tablets come in packs for 91 days resulting in a “period” once every 3 months.

In either case, it is important to speak with your healthcare provider to ensure taking an extended period of birth control is a good option for you and your health. Sometimes, insurance companies will not allow you to take your birth control back-to-back. In this case, your healthcare provider may be able to specifically write a prescription detailing the reason for this choice and insurance may allow it.

Comparing Common Side Effects

It can be difficult to compare side effects between monophasic and biphasic birth control, as they both have variation within their groups, depending on the type of progesterone and strength of the medications. In general, monophasic and biphasic birth control pills have similar but slightly different side effects. Though not every patient will experience any or all of these effects, it’s good to know what you may experience while on either medication.

Using monophasic and biphasic pills containing levonorgestrel as direct comparison, the most common side effects with each of the contraceptive pills, from most likely to less likely, include:

Monophasic

• Headache
• Heavier/prolonged menstrual periods
• Nausea
• Painful periods

Biphasic

• Irregular/ heavy menstrual periods
• Weight gain
• Acne

Comparing the Price of Monophasic and Biphasic Pills

This question would have a different answer depending on your own personal preferences. However, there are a number of things to consider, which are outlined here.

Prices mentioned in this article are based on average retail price at major box chain pharmacy in the U.S. as of May 31, 2023.