People stopping weight-loss injections such as Mounjaro or Wegovy may notice fatigue, or feeling unusually tired, as a common side effect of the medicines, according to NHS guidance.
The NHS lists feeling tired among the common side effects of both semaglutide medicines such as Wegovy and tirzepatide, sold under the brand name Mounjaro. However, feeling exhausted after stopping treatment could have several possible explanations, rather than automatically meaning someone is experiencing withdrawal.
How the medicines work
The NHS does not describe fatigue as a specific withdrawal symptom from semaglutide or tirzepatide, while NHS guidance says people should speak to their doctor before stopping either medicine rather than stopping suddenly. Semaglutide works partly by reducing appetite and slowing digestion, while tirzepatide activates GLP-1 and GIP receptors and can help people feel fuller for longer, according to the NHS.
Both medicines can cause tiredness while they are being taken, with the NHS listing feeling tired among their common side effects. Cambridge University Hospitals, which provides NHS care, says feeling weak or tired is common in patients taking tirzepatide and says this may be linked to people consuming fewer calories and therefore having less energy.
Changes after stopping treatment
There can also be important changes after treatment stops, particularly for people using these medicines to manage their weight or diabetes. NHS guidance says anyone considering stopping semaglutide should speak to their doctor and not stop suddenly, while people taking tirzepatide are similarly advised to talk to their doctor because stopping can affect blood sugar when it is being used for type 2 diabetes.
Research has also found that weight regain can occur after semaglutide treatment ends, although the amount varies between individuals. A follow-up of the STEP 1 trial found participants regained around two-thirds of their previous weight loss within a year of stopping semaglutide, with some of the improvements in cardiometabolic measures also moving back towards baseline.
Support and advice
The study followed 327 participants for a year after treatment was withdrawn, with the researchers describing the analyses as exploratory. According to the NHS, people stopping weight-loss medicines should be offered support to help them maintain a healthy weight, rather than simply being left without follow-up. This does not mean everyone who stops treatment will regain the same amount of weight, and research published since the original STEP 1 extension has also found variation between individuals following discontinuation.
Anyone experiencing persistent or unexplained tiredness should not automatically blame their medication history, as the NHS says fatigue can have many causes and advises speaking to a GP if it continues for several weeks or affects daily life. People taking these medicines should also follow advice from their own prescriber, particularly if they are using treatment to control type 2 diabetes, because stopping can affect blood sugar levels.
