Learn what a washout period is and how long to wait when switching between GLP-1 weight-loss medications.

If you're moving from one GLP-1 medication to another, you'll need a short pause between stopping one and starting the next. This is called a washout period, and it's an important safety step in your treatment.

Here's what a washout period involves, how long it lasts, and how to manage your body while you wait.

A washout period is a planned pause between stopping one medication and starting another. During this interval, your body is given the time it needs to clear, or "wash out", the previous treatment so it is less likely to influence how the next medicine works.

When switching between GLP-1 receptor agonists such as semaglutide (Wegovy) or tirzepatide (Mounjaro), washout periods are a crucial safety measure.

These medications have long half-lives - the time it takes for the amount of a drug's active substance in your body to reduce by half. Starting a new treatment too soon can cause problems, so a well-timed washout period helps to mitigate these risks.

Clearing the previous medication allows your prescriber to monitor progress accurately, and understand which effects belong to the new treatment.

At Phlo, we recommend a 7-day washout period from your last dose of the previous GLP-1 medication before you start your new GLP-1 treatment. This minimises side effects and aids a smooth transition between the medications.

This applies whether you are moving from Wegovy (semaglutide) to Mounjaro (tirzepatide), or from Mounjaro (tirzepatide) to Wegovy (semaglutide).

This balances safety and practicality: it gives sufficient time for most of the prior drug's activity to decrease, helping to reduce the risk of overlapping effects and side effects. After the washout, you begin your new medication at the starting dose recommended by our prescribers, ensuring a controlled and clinically supervised transition.

As your previous medication clears from your system, several physiological changes may occur. These are generally expected and temporary, but being aware of them can help you manage the transition with confidence.

Because GLP-1 agonists have long half-lives, their therapeutic effects diminish slowly rather than abruptly. You may notice subtle shifts in your appetite, digestion, or energy levels as the active drug level in your body decreases.

Depending on why you were using the medication, some symptoms may start to return. Appetite suppression may lift, meaning your hunger could increase, and portion sizes or cravings might change. Mild digestive changes such as altered gut motility are also common, though usually short-lived and tend to resolve as your body rebalances.

Managing a washout period well requires a combination of self-care, close observation, and clear communication with our healthcare team. Though the pause is temporary, using the time wisely can make the transition smoother and more comfortable.

Pay close attention to changes in appetite, digestion, or energy. Using a simple journal, health app, or chart to record your observations - such as hunger levels, meal sizes or cravings - provides valuable data to tailor your care.

Lifestyle strategies are powerful during this phase. Focus on well-balanced meals that include lean proteins, fibre, and healthy fats to stabilise appetite. Stay hydrated, and prioritise good sleep hygiene. Light to moderate exercise, such as walking or gentle strength training, can support metabolic balance and help regulate hunger. Mindful eating and portion control also help ease your body through the transition.

It's critical to follow your prescribed washout timeline exactly. Beginning your new medication too early can raise the risk of gastrointestinal discomfort, such as nausea or vomiting, or other compounded side effects. Adhering to the recommended washout period ensures your body has truly reset, making your new treatment as safe and effective as possible.

Before starting your new medication, make sure you have precise instructions from our clinician team, including when to restart and at what dose. If anything is unclear or you feel uncertain, contact the Phlo team - clarifying before starting is far safer than guessing.

Your healthcare team should remain your principal source of support during this time. If you experience any concerning symptoms, such as severe nausea or digestive issues, contact your healthcare provider. Regular check-ins offer reassurance, help adjust your plan if needed, and ensure you're ready for your next treatment phase confidently.

A washout period is more than just a break, it's a purposeful reset. It gives your body the space to adjust, stabilise, and prepare for the next stage of treatment. By allowing this short transition phase, you help create the right conditions for your upcoming therapy to work more smoothly and effectively.

If you're unsure about your washout timing or dosing, get in touch with the Phlo team at [email protected] before starting your new medication. It's always safer to check than to guess.