Can you start Mercilon anytime? Understanding your contraceptive options

October 10, 2025 •

5 min read

According to the NHS, you can start taking the combined pill at any point during your menstrual cycle, as long as you're certain you are not pregnant. This fact is key to understanding how to begin using Mercilon and when you can rely on its contraceptive protection.

Quick Summary

This guide explains the different starting methods for Mercilon, a combined contraceptive pill, and outlines the required waiting period for protection based on when you begin taking it. It also covers what to do when switching from other contraception or if pills are missed.

Key Points

Start anytime, but with a caveat: You can start Mercilon at any point in your menstrual cycle, but immediate contraceptive protection is not guaranteed unless you start on the first day of your period.
Start on Day 1 for instant protection: If you take your first Mercilon pill on the first day of your menstrual period, you are immediately protected against pregnancy.
Quick start requires caution: If you start Mercilon on any day other than day one of your period, you must use additional contraception, like condoms, for a specific period.
Understand switching protocols: When moving from a different type of contraception, the timing and need for backup contraception varies; for example, switching from a progestogen-only pill may require a period of additional protection.
Missed pills reduce effectiveness: If you miss a pill by more than 12 hours, your protection may be reduced, and you will need to use backup contraception for a specific period.
Maintain consistency for best results: For maximum effectiveness, Mercilon should be taken at the same time every day, whether you are on a standard cycle with a break, or a continuous regimen.

Can You Start Mercilon Anytime? The Different Starting Methods

While it is possible to begin taking the combined contraceptive pill Mercilon at any point in your menstrual cycle, the level of immediate protection you receive depends on the timing. To ensure maximum effectiveness and safety, it is crucial to understand the standard starting methods and follow the instructions provided by your healthcare provider and the patient information leaflet.

The 'Day 1' Start: Immediate Protection

The most straightforward method for starting a new pack of Mercilon is the 'Day 1' start. This involves taking your very first pill on the first day of your menstrual period. By doing so, you are protected from pregnancy immediately and do not need to use any additional contraception. This method works by ensuring the hormones begin suppressing ovulation right at the start of your cycle, leaving no window for an egg to be released.

The 'Quick Start' or 'Anytime' Start: Delayed Protection

If you begin taking Mercilon at any other point in your cycle (from day 2 onwards), you are using the 'Quick Start' method. This is also known as an 'anytime' start. The main difference is that you will not be protected from pregnancy right away. Instead, you must use a barrier method of contraception, such as condoms, for a specific period. After you have taken a certain number of active pills, you are considered protected. Before using this method, a healthcare provider should confirm you are not pregnant.

Switching from other contraceptives

Moving from another form of birth control to Mercilon requires different starting procedures to ensure continuous protection. The method depends on what type of contraception you were previously using.

From another combined pill: Start Mercilon the day after taking your last active pill from your previous pack. This avoids a break between packs and provides immediate contraceptive protection.
From a progestogen-only pill (mini-pill): You can switch to Mercilon any day. If you start Mercilon on the first day of your period, you are immediately protected. If you switch on any other day, you must use additional contraception for a specific period.
From an implant, injection, or IUD: You can start Mercilon on the day your implant or IUD is removed, or on the day your next injection would have been due. In all these cases, you must use a barrier method for a specific period.

Comparison of Mercilon Starting Methods


Starting Method	Timing	When You Are Protected	Additional Contraception Needed	What to do if you have sex beforehand	Notes
Day 1 Start	Take first pill on the first day of your period.	Immediately protected.	No additional protection needed.	N/A.	Safest starting method, offers immediate protection.
Quick Start / Anytime	Take first pill on any other day of your cycle.	After taking a specific number of consecutive pills correctly.	Yes, use condoms for a specified period.	Take a pregnancy test to ensure you are not pregnant before starting.	Provides flexibility, but requires a waiting period for full effect.
Switching from another combined pill	Start the day after the last active pill of your old pack.	Immediately protected.	Not needed, assuming the previous pill was taken correctly.	N/A.	Ensures continuous contraceptive coverage.
Switching from mini-pill (POP)	Start on the first day of your period or the day after your last mini-pill.	Immediately protected if starting on day 1 of period. If starting any other time, after taking a specific number of pills.	Yes, for a specified period if not starting on day 1 of your period.	If switching at any time other than the start of your period, use condoms for a specific period.	Offers flexibility in transitioning, but requires attention to timing.

What to do if you miss a Mercilon pill

Missing a pill can reduce the effectiveness of Mercilon, and what you should do next depends on when the pill was missed.

Missed by less than 12 hours: Take the pill as soon as you remember. Continue with the rest of the pack at your regular time. Your contraceptive protection should not be affected.
Missed by more than 12 hours: Take the last missed pill as soon as you remember, even if it means taking two pills in one day. Use additional barrier contraception (like condoms) for a specific period.
Missed multiple pills: If you miss two or more pills, your contraceptive protection is compromised. Consult the patient information leaflet or a healthcare professional for specific instructions, which may involve using extra contraception for a certain period and potentially skipping the pill-free interval.

Potential Side Effects of Mercilon

Like all medications, Mercilon can cause side effects, though not everyone will experience them.

Common side effects: Headaches, nausea, breast tenderness, and mood swings are among the more frequent side effects, particularly when starting the pill. These often improve after a few months as your body adjusts.
Breakthrough bleeding: Some women may experience irregular bleeding or spotting, especially on a continuous regime or during the first few packs. This is usually temporary. If it persists, consult your doctor.
Rare but serious side effects: The combined pill carries a rare risk of blood clots, particularly for smokers over 35, those with high blood pressure, or those with certain medical conditions. It is essential to discuss your medical history with your doctor before starting any combined pill.

Conclusion: Safe Usage Requires Understanding Timing

In conclusion, while you can start Mercilon anytime, the timing of when you begin directly impacts when you will be protected from pregnancy. A 'Day 1' start on the first day of your period offers immediate protection, whereas a 'Quick Start' at any other time requires a period of using additional contraception. When switching from other methods or dealing with missed pills, specific protocols must be followed to maintain effectiveness. Always consult a healthcare professional to determine the safest and most effective starting method for your personal situation. Being informed about these different starting options and consistently taking your pill correctly are the most important steps to ensure reliable contraception.

For more detailed guidance on a wide range of contraceptive options, consider visiting the NHS website to discuss your choices with a healthcare professional.

Frequently Asked Questions

If you start Mercilon on the first day of your period, you are protected from pregnancy immediately. If you start on any other day of your cycle, you must use additional contraception, such as a condom, for a specified period of pill-taking.

You only need to use condoms for a specified period if you start taking Mercilon on any day other than the first day of your period. If you start on the first day of your period, you have immediate contraceptive protection.

If you miss a pill by less than 12 hours, take it as soon as you remember and continue as normal with no loss of protection. If it's more than 12 hours, take the last missed pill immediately, continue the pack, and use extra contraception (e.g., condoms) for a specific period.

Yes, you can skip your period by running two or more packs of Mercilon together without a pill-free interval. This method is safe, but you may experience some breakthrough bleeding.

A Day 1 start, beginning on the first day of your period, provides immediate contraceptive protection. A Quick Start, beginning on any other day, requires you to use additional contraception for a specific period to be protected.

Yes, Mercilon can still be effective, but not immediately. If you are not on your period when you start, you will need to use a backup contraceptive method for a specific period of use.

The duration until protection depends on your start day. You are protected immediately if you start on day 1 of your period. If you start on any other day, protection begins after you have taken a specified number of consecutive active pills.