How do the risks of taking Wegovy compare with taking other weight loss medications?

The most common side effects with Wegovy are gastrointestinal, such as nausea and diarrhoea, and these often lessen over time. Other medicines have different risks: Orlistat can cause oily stools, Mysimba may raise blood pressure, and phentermine (not used in the UK) carries cardiovascular risks.

Understanding risk in context

All weight-loss medicines come with benefits and risks. Doctors weigh these carefully before prescribing, taking into account a person’s health conditions, medical history, and preferences. Wegovy, as a GLP-1 receptor agonist, shares some similarities with older drugs but also differs in important ways. Comparing its risks with other medicines helps clarify where it stands.

Wegovy’s side-effect profile

Wegovy (semaglutide 2.4 mg weekly) most often causes gastrointestinal side effects — nausea, diarrhoea, vomiting, or constipation — especially during dose escalation. In the STEP-1 trial, around 74% of participants reported some GI symptoms, though most were mild or moderate, and only a small number stopped treatment because of them. These effects usually ease as the body adjusts, which is why doses are stepped up gradually over 16 weeks. Rare but more serious risks include gallbladder issues and, in uncommon cases, pancreatitis.

Orlistat’s risks

Orlistat works by blocking the absorption of fat in the gut. While effective for modest weight loss, it often causes oily stools, flatulence, and an urgent need to go to the toilet if too much fat is eaten. These side effects can be socially disruptive and are a main reason people stop using it. Orlistat is generally safe for the heart but offers limited benefits for metabolic health compared with GLP-1 therapies.

Mysimba’s risks

Mysimba (naltrexone/bupropion) acts on the brain’s reward pathways to reduce cravings. Its side-effect profile is different: it can raise blood pressure, increase heart rate, and sometimes cause insomnia or anxiety. For this reason, it is not suitable for people with uncontrolled hypertension or certain mental health conditions. Its weight-loss results are more modest, averaging 6–9% in trials, which means the risk-benefit balance is less favourable for some groups.

Phentermine’s risks

Phentermine, still used in some countries but not licensed in the UK, is a stimulant-like medicine that suppresses appetite. It can raise heart rate and blood pressure and carries risks of dependence. For safety reasons, it is typically prescribed only for short-term use under close supervision. These cardiovascular concerns are a key reason it has not been adopted in UK clinical practice.

Why Wegovy stands out

While Wegovy does cause gastrointestinal side effects, its long-term safety record is stronger than that of many older medicines. Importantly, semaglutide has been shown not only to help with weight loss but also to reduce cardiovascular events, as seen in the SELECT trial. This means that its risks are offset by proven benefits in heart health — a balance not achieved by drugs like Orlistat, Mysimba, or phentermine.

The full perspective

In summary, Wegovy’s main risks are digestive and usually improve over time, while other medicines bring different concerns such as oily stools (Orlistat), raised blood pressure (Mysimba), or cardiovascular strain (phentermine). Compared with these, Wegovy offers both stronger weight-loss outcomes and added heart health benefits, making it a more favourable option for many people when prescribed under NHS or specialist guidance.