January 7, 2026, 3:03 am | Read time: 5 minutes
The GLP-1 injection as a shortcut to the desired weight–what many now consider a lifestyle drug is actually a prescription medication–with risks, side effects, and clear limits. In a FITBOOK interview, study insider Prof. Norbert Stefan warns against fatal misconceptions and counterfeit drugs from abroad.
Endocrinologist and diabetologist Prof. Dr. med. Norbert Stefan is one of the leading experts on the clinical study landscape and mechanisms of GLP-1-based medications. He holds the chair of clinical-experimental diabetology at the University Hospital Tübingen and heads the “Pathophysiology of Prediabetes” department at the Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich. He has collaborated with manufacturers of GLP-1-based preparations, mostly in the context of scientific lecture events. The last part of the interview addresses myths surrounding GLP-1.
»The Injection Is No Miracle Cure
FITBOOK: Is there something fundamentally wrong in the public debate about the “weight loss injections” from your perspective?
Prof. Dr. med. Norbert Stefan: “The biggest misunderstanding, in my view, is the notion that these medications are a kind of miracle cure–especially for rapid weight loss. Many see before-and-after pictures and believe that one only needs to regularly inject to be permanently slimmer and healthier. It is often forgotten that these are prescription medications with clear medical indications–type 2 diabetes, overweight (specifically BMI ≥27 kg/m2) with existing weight-related comorbidities such as dysregulation of glycemic control (prediabetes or type 2 diabetes), hypertension, dyslipidemia, obstructive sleep apnea, cardiovascular disease, or obesity.”
Also of interest: Norbert Stefan – Interview Part 1 »Greatest Impact of GLP-1 Medications on These Patients
»No Proven Preventive Effect for Healthy Individuals
Does the weight loss injection also protect healthy individuals–or is that a misconception?
“That is also a misunderstanding. It is currently not proven that GLP-1 medications have a preventive effect against heart attack, diabetes, or Alzheimer’s in healthy people without pre-existing conditions. The studies available so far relate exclusively to already ill individuals.”
»Without Behavioral Change, the Weight Returns
If I belong to the patient group for whom the weight loss injection is considered or prescribed: What should I do beyond the injections?
“Lifestyle change is extremely important. In all studies on weight reduction and therapy of MASH [inflammatory liver disease where fat accumulates in the liver, ed.], on which the approvals are based, the intake of the medications was linked to a consistent lifestyle change–that is, calorie reduction, dietary changes, and regular physical activity. Most participants in the weight reduction studies had a structured program–sometimes with a recommendation of about 1,200 kilocalories daily and at least 150 minutes of exercise per week. Without these accompanying measures, long-term success is significantly lower.”
What happens if you stop the weight loss injection but don’t change your behavior?
“If the medication is simply discontinued without a change in behavior, weight gain often occurs again. Therefore, it is medically sensible to always embed this therapy in a holistic treatment concept.”
Also of interest: Norbert Stefan – Interview Part 2: »The Most Common Side Effects of the Weight Loss Injection
„I View This with Great Concern“
More and more people are obtaining GLP-1 medications online. How dangerous are counterfeit weight loss injections from abroad?
“I view this with great concern. In the U.S., pharmaceutical companies or pharmacies are allowed to compound and sell medications during shortages, known as ‘compounded drugs.’ These are often preparations that do not meet the same quality standards as the originals and have not been tested in clinical studies. This potentially poses significant risks to efficacy and safety. Fortunately, this is not allowed in Europe. However, we are also seeing an increase in people trying to obtain these medications, often without sufficient medical supervision, through online providers. This is a problem because these are not often harmless dietary supplements but effective medications with possible side effects.”
»Before-and-After Pictures Create False Expectations
What impact do before-and-after photos of celebrities have on the perception of these medications?
“The media focus on before-and-after photos suggests a one-sided image: the injection as a panacea for a better life. There is little discussion about what pre-existing conditions the individuals had, what side effects occurred, or how difficult long-term weight stabilization is. This is problematic because it raises unrealistic expectations–and puts pressure on people who may not even have a medical indication.”
“The Most Common Side Effects of the Weight Loss Injection”
“Greatest Impact of GLP-1 Medications on These Patients”
„What I Cannot Recommend Is the Self-Directed Use Without Indication“
When you see everywhere how quickly others lose weight with GLP-1 agonists, it’s easy to think: Why not me too? What do you say to people at that moment?
“I would advise these people to seek a conversation with their primary care physician. Particularly people with poorly controlled type 2 diabetes and/or overweight/obesity and cardiovascular pre-existing conditions should, in my view, have a medical examination to determine if such therapy is suitable for them. If there are uncertainties, visiting a diabetological or endocrinological specialist practice is advisable. What I cannot recommend is the self-directed use of GLP-1 agonists without a clear indication and without medical supervision. The risks are often underestimated–even if the short-term success on the scale seems tempting.”
»Great Potential–But Only with Controlled Use
What do you see as the biggest challenge if GLP-1 therapies become even more readily available in the future?
“A major issue will be the broad availability. It is already foreseeable that significantly more people will want such therapy than actually have a medical indication. If GLP-1 medications become available in tablet form in the future, the threshold could further decrease. This increases the risk of uncontrolled self-medication. At the same time, I see it as problematic if medications are taken without adequate accompanying medical supervision–whether through online portals or from abroad. The medical potential of these preparations is great, but it can only be fully realized if the application is controlled and individually tailored.”