Yes, Plan B (levonorgestrel) may lead to a delayed period or induce bleeding outside the typical menstrual cycle, as it contains a synthetic hormone. In order to prevent pregnancy, Plan B, similar to other contraceptive pills, needs to modify your hormonal levels, which can result in these menstrual alterations. It's worth noting that Plan B is linked to a higher likelihood of menstrual changes compared to regular birth control pills, due to its increased dosage.

Changes in the menstrual cycle

In a clinical trial, 31% of participants experienced some change in their menstrual cycle after taking Plan B, but the potential menstrual changes are varied. Plan B may cause some women to experience heavier or lighter menstrual bleeding compared to their regular periods.

After taking Plan B, some women get their period sooner than expected, while others get it later. However, clinical trial data suggest most women will get their period within two days to one week of the anticipated time. Women who take Plan B and experience a delay in their period greater than one week are recommended to take a pregnancy test.

During your menstrual cycle, the time at which Plan B is taken can affect how your menstruation changes.

• Some studies suggest that taking Plan B early on in your menstrual cycle can increase the likelihood of spotting before menstruation begins and can sometimes cause the next period to be shorter than usual.
• When Plan B is taken later in your menstrual cycle, it may not affect period length, or it may be more likely to result in prolonged menstrual bleeding.

Spotting

Non-menstrual bleeding, or spotting, can also occur after using Plan B. Clinical trial data show that 16% of participants experienced spotting in the first week after taking Plan B. Similarly, in one study of 232 women who took Plan B, just under 15% experienced spotting. In this study group, the bleeding typically started around 4 days after Plan B was taken and lasted an average of 2.4 days, with a range of one to seven days. Some women began spotting as early as 8 hours after taking Plan B.

Menstrual changes and irregular bleeding associated with Plan B should go away without treatment. In one study of 132 women, most women returned to their normal cycle length in the next cycle following the use of Plan B. However, those who took Plan B later on in their cycle (after ovulation) had a slightly longer next cycle on average.