Stopping a Weight Loss Pen: Will the Weight Come Back?

Weight can genuinely return after stopping a weight loss pen. The STEP 1 trial extension found that one year after semaglutide was withdrawn, participants had regained roughly two-thirds of the weight they had lost. The main reason is that appetite returns to its previous level once the medication is no longer acting — not a failure of willpower.

Will the weight come back after stopping?

The direct answer is that partial regain is likely, and the clearest figures on this come from the extension of the STEP 1 trial, which continued following participants after treatment stopped.

In the main trial, participants receiving weekly semaglutide alongside lifestyle intervention lost an average of 17.3% of body weight over 68 weeks. When both the medication and the lifestyle programme were then withdrawn and participants followed to week 120, weight returned by an average of 11.6 percentage points, leaving a net loss of 5.6% from baseline.

Another figure worth knowing is the spread between individuals. Around 17.7% were back at or above their starting weight, while others held varying amounts of their loss. Regain is therefore not the only possible outcome — but it is a tendency worth planning for in advance.

Why does weight return?

The reason lies in the mechanism itself. GLP-1 medications work by signalling fullness and slowing gastric emptying for as long as the drug is active. Once stopped, that mechanism is gone: appetite and hunger signals return to the body’s baseline, and the amount you can comfortably eat per meal returns close to what it was.

The second factor is metabolic adaptation. A lighter body uses less energy at rest than a heavier one did. Returning to the same portions as before starting therefore tips the energy balance positive more easily than it used to.

The third factor is muscle mass. Losing weight by reducing energy intake usually costs some muscle unless protein intake and resistance training are actively managed. Less muscle means slightly lower resting energy use again.

Put together, regain is a predictable physiological response rather than purely a question of resolve. Understanding this matters, because it shifts the plan from self-blame to building a system in advance.

Do trial data and real-world data agree?

Not entirely, and the difference is useful for setting expectations.

An important detail of STEP 1 is that participants stopped the medication and the lifestyle programme at the same time — unlike the situation where someone stops the drug but keeps the eating and exercise patterns they built. That difference likely explains part of why real-world outcomes are more varied.

What both sets of data agree on is that the medication does not reset the body’s baseline in the way many people assume, and that results do not hold automatically. Outcomes depend on the individual, and there is no guarantee that weight will stay stable after stopping.

Do I need to use it indefinitely?

Not necessarily, and it is not a decision to fix in advance without assessment. Current medical thinking treats obesity as a chronic condition requiring ongoing care, similar to high blood pressure or high cholesterol, where stopping treatment is often followed by return of the underlying condition.

In practice, duration depends on several things: the weight target, weight-related complications, response to the medication, side effects experienced, and how well new habits can be sustained. Some people use the medication for a period to get past a point they could not manage by behaviour change alone; others need longer.

How to hold the results after stopping

The time on medication is when hunger is easier to manage, which makes it the right window to lay foundations — not a period to put habits on hold.

1. Eat enough protein at every meal to preserve muscle while total intake is lower
2. Train with resistance regularly, since muscle mass is what supports resting energy use
3. Build an eating pattern you can actually maintain afterwards, rather than heavy restriction that only works with the drug’s help
4. Sleep adequately, as sleep loss is associated with altered hunger hormones
5. Weigh yourself periodically to catch upward drift early, rather than noticing once you are back where you started
6. Plan stopping with your doctor rather than stopping abruptly, so follow-up continues

When to go back to your doctor

If weight rises steadily over several weeks back toward the starting point, if appetite becomes strong enough that eating patterns are hard to hold, or if conditions that improved on the medication — blood sugar or blood pressure, for instance — start worsening again, those are the moments to be reassessed. They are not moments to restart medication on your own.

Going back does not necessarily mean returning to medication. In some cases adjusting diet and exercise is enough; in others the doctor may consider other approaches. It depends on individual assessment.

Planning it with a doctor

If you are using a weight loss pen and starting to think about stopping, or considering starting and want to understand the long-term picture first, discussing it early gives a clearer plan than deciding at the point you already want to stop.

Consult a doctor at Onnyx Clinic for an individual assessment covering both the treatment period and what follows. Ask via LINE: @onnyxclinic

References

• Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension (Diabetes, Obesity and Metabolism)
• STEP 1 trial extension (PubMed)
• Many Patients Maintain Weight Loss a Year After Stopping Semaglutide and Liraglutide (Epic Research)
• Tirzepatide Once Weekly for the Treatment of Obesity — SURMOUNT-1 (NEJM)
• Thai Food and Drug Administration