Are Ozempic and similar medications dangerous? What does the science actually say?

What exactly are these new weight-loss medications everyone’s talking about?

Weight-loss medications aren’t some newly discovered drugs with unknown mechanisms. GLP-1 agonists have actually been used for over 15 years, primarily to treat type 2 diabetes. They work by mimicking the natural hormone GLP-1 in our body, which slows down how quickly the stomach empties, helps you feel full longer, and reduces appetite. At the same time, they improve blood sugar control by increasing insulin release and lowering glucagon levels.

This combination—food staying in the stomach longer and a reduced desire to eat (including fewer cravings)—is what leads to relatively faster weight loss.

What was used for weight loss before, and how did these new medications come into the picture?

Before GLP-1 agonists, obesity treatment was mainly based on diet, physical activity, and older medications like orlistat, which had limited effectiveness and, unfortunately, frequent side effects. It’s important to point out that Ozempic is approved for treating type 2 diabetes and is covered by insurance only under specific criteria—typically in patients whose blood sugar (HbA1c) remains poorly controlled despite existing therapy, such as metformin.

Medications specifically approved for weight loss came later. In practice, this includes liraglutide (daily injections), as well as semaglutide and the newer tirzepatide (both weekly injections). Tirzepatide targets both GLP-1 and GIP receptors and, as seen in clinical use, tends to lead to faster weight loss—though often with more side effects as well.

Metabolic effects and benefits

GLP-1 medications have multiple effects, with the main benefits including weight loss of about 10–20% of body weight (depending on the drug and dose), improved insulin resistance, better lipid profiles, and a reduction in overall cardiovascular risk.

Their effects on blood lipids are mostly indirect—through weight loss and improved insulin sensitivity—but they also have some direct metabolic actions. They help lower triglycerides by reducing post-meal fat levels (thanks to slower gastric emptying and reduced food intake), and they can lower LDL (“bad cholesterol”) as weight loss leads to decreased production of LDL in the liver. However, the largest impact comes from the loss of visceral fat—the deeper abdominal fat—which reduces inflammation and improves the overall metabolic profile.

Cardiovascular outcome studies have also shown a reduced risk of heart attack and stroke in people with diabetes. A common counterargument is that we don’t fully know how these mechanisms apply to otherwise healthy individuals. But today, about 1 in 10 people has diabetes, while 25–40% have insulin resistance, and 30–40% have abnormal lipid levels. Early signs of atherosclerosis have even been found in infants over the past decades—meaning most metabolic problems begin long before diabetes develops, and are increasingly influenced by diet and lifestyle, even during pregnancy and early life.

The real truth? Our genes are still shaped by the eating patterns of our ancestors. Looking back just three or four generations, it’s clear that our metabolism isn’t designed to handle constant intake of simple sugars, fast food, sugary drinks, fried foods, and processed baked goods—without the body eventually compensating, often through the development of metabolic and endocrine diseases.

Does Ozempic “eat away” at your bones?

Yes and no—it depends on how they’re used. GLP-1 agonists can lead to some loss of bone and muscle mass, but in many cases their impact is minimal. What really matters is how the weight is lost. Rapid weight loss (for example, 30 kg in 4–5 months), without proper training, can weaken bones regardless of whether it’s achieved with medication or extreme dieting and very low calorie intake. In both cases, the risk of gallstones also increases.

Weight loss with GLP-1 therapy does include some loss of lean mass. On average, about 70–80% of the weight lost is fat, while 20–30% comes from muscle mass. This applies to the general population without structured exercise. In people who train regularly—especially with resistance training—that ratio shifts, helping preserve muscle. With 2–3 strength sessions per week and regular activity, muscle loss is significantly reduced, and the negative impact on bone is largely minimized.

A recent 2025 meta-analysis in patients with type 2 diabetes found that GLP-1 agonists did not increase fracture risk and were even associated with better outcomes in BMD (bone mineral density—a measure of bone strength assessed by DEXA scans) and certain markers of bone turnover compared to controls. This doesn’t mean they “protect” bone in every situation, but it does argue against the idea that these medications inherently damage bone.

In practice: GLP-1 therapy + resistance training + adequate protein intake = preservation of muscle and bone, with weight loss coming primarily from fat.

Risks and side effects

The risk of hypoglycemia (a sudden drop in blood sugar) is very low when GLP-1 medications are used on their own (without other diabetes drugs), especially if patients eat regular, smaller meals rich in protein and complex carbohydrates. These medications are not meant to be used alongside extreme approaches like skipping meals entirely, juice cleanses, or cutting out all carbohydrates.

Instead of skipping breakfast—or grabbing a croissant or bakery sandwich—a better option is something like cottage cheese with nuts, 1–2 eggs with vegetables, or a protein shake if appetite is low. The most common side effects—nausea, diarrhea, and bloating—are often linked to continuing an unhealthy diet (refined carbs, fast food, chips, sugary drinks), and can usually be reduced by switching to meals higher in protein and fiber.

As mentioned earlier, the risk of gallstones increases with rapid weight loss, regardless of the method used. With GLP-1 therapy, it’s recommended to monitor labs (glucose, HbA1c, liver enzymes) every 3–6 months. If symptoms like sudden upper abdominal pain, nausea, vomiting, or pale/yellowish stools occur, an earlier abdominal ultrasound should be considered.

With GLP-1 therapy, the goal of breakfast is: small in volume, nutrient-dense, easy to digest, and rich in protein and fiber.

Recently, there has been discussion about a very rare but serious side effect linked to GLP-1 medications—a sudden loss of vision caused by impaired blood flow to the optic nerve (known as NAION). This is an extremely rare condition, estimated to occur in about 1 in 10,000 users. It’s important to emphasize that this is an association, not a proven cause, since many of these patients already have underlying risk factors such as diabetes, high blood pressure, and abnormal cholesterol levels.

While some analyses suggest a higher risk at higher doses, the key recommendation remains the same: therapy should be started gradually and always under medical supervision. These medications should never be obtained independently and started at the highest available dose without proper guidance.

Who should NOT take GLP-1 medications?

The main absolute contraindication for these medications is a personal or family history of medullary thyroid cancer (including cases in close relatives such as parents or grandparents), as well as individuals with MEN2 syndrome. Caution is also advised in patients with existing gallstones or severe gastrointestinal conditions.

GLP-1 medications represent a significant advancement in the treatment of obesity and metabolic disorders, but it’s important to emphasize that they are not a “magic solution.” The benefit–risk balance favors their use in individuals with a BMI over 30, particularly when weight loss has not been achieved through diet and regular physical activity, or in those with documented metabolic conditions such as insulin resistance, prediabetes, hypothyroidism, and others. The best results are seen when these medications are combined with a balanced diet (higher in protein and fiber, lower in simple sugars), regular physical activity, and properly guided therapy.

This approach allows for a structured, comprehensive treatment of obesity that not only improves effectiveness but also reduces side effects like nausea and digestive discomfort. In summary, using these medications without proper indication (e.g., BMI ≥30), increasing doses too quickly or starting at high doses, maintaining an unhealthy diet, or skipping meals altogether are not aligned with good clinical practice and can lead to unwanted outcomes. Likewise, taking these medications without introducing regular physical activity (at least walking, swimming, or treadmill exercise 3 times per week, ideally combined with strength training) increases the risk of losing muscle—and potentially bone—mass.

GLP-1 medications do not act as a “bone-dissolving” agent. What actually happens is that rapid weight loss reduces the mechanical load on bones, which can lead to some loss of bone density if not supported by resistance training and adequate protein intake. For that reason, these medications should not be used passively, without attention to physical activity, protein intake, and, in some cases, supplementation (such as vitamin D3 and K2) during periods of more rapid weight loss.

You are what you eat is a phrase popularised by the German philosopher Ludwig Feuerbach as early as the 1850s, although the roots of this philosophical principle can be traced back to Hippocrates. Indeed, on days when we are overwhelmed by work and obligations, when we “have coffee for breakfast,” skip lunch, and spend a spare minute or two on a cigarette or a chocolate doughnut, we should not expect to feel energetic or at the peak of our abilities. If we add an energy drink to the mix, it is not long before we notice hand tremors, difficulty concentrating, and possible digestive problems—ranging from acid reflux to painful abdominal cramps.

The fact is that technological progress—and with it the production, transport, and storage of food, as well as innovations such as frozen bakery products baked on the day of purchase, still soft, warm, and fragrant—has advanced far more quickly than our genes can adapt. Just a few generations ago, bread was a treat made once or twice a week; diets were based on stews and vegetables, with meat added sparingly, often more for flavour than quantity. Meat was boiled or roasted; deep-frying was not a common method of preparation. Desserts relied on fruit or simple sponge cakes with fruit fillings. A pistachio-filled doughnut? Unthinkable at the time.

Although meat drying for preservation, as well as the early forms of dishes like steak tartare, date back to distant history, the first processed meats—such as sausages, cold cuts, and pâtés—associated with carcinogenic effects appeared in the early 20th century. While the high salt content of these products has a negative impact on health (for example, raising blood pressure), the real culprits behind their carcinogenic potential are nitrates and nitrites.

A fresh-looking extra pink steak on the shelf is probably the worst choice you could make!

Although nitrates and nitrites were originally added as preservatives (for example, to inhibit the growth of C. botulinum), today they are used in increasingly larger and more problematic amounts, primarily for visual appeal. They stabilise and prolong the familiar pink-red colour that makes meat look “fresh” even after sitting on a shelf for weeks. In addition, they act as flavour enhancers, intensifying the characteristic “sausage-like” taste of meat products.

The end result is that meat—often imported long ago and of lower, sometimes questionable quality simply because it has been stored for so long—can be attractively packaged and sold while still appearing fresh, thanks to artificially enhanced colour. Such products not only carry a risk of carcinogenic effects, but also aggressively undercut domestic, higher-quality meat products on price. These local products may have only just reached the market and may not appear as vividly pink or “fresh,” yet they are nutritionally and qualitatively superior.

CAUSES OF CARCINOGENICITY

Why are nitrites and nitrates carcinogenic, and why primarily to our large intestine? When they come into contact with haem iron (abundant in red meat) and proteins in the gut, they are converted into so-called N-nitroso compounds (NOCs). These NOCs are carcinogenic to the digestive tract, particularly to the lining of the colon and rectum.

NOCs formed in the intestine cause DNA damage in the cells of the intestinal mucosa, leading to mutations. The development of mutations is the first step in the transformation of a normal cell into a cancer cell. If such a cell begins to multiply uncontrollably, carcinoma in situ may develop initially, without penetrating the bowel wall. Over time, further spread allows the tumour to invade the intestinal wall and metastasise to lymph nodes and/or other organs.

Because gut bacteria promote the formation of NOCs—and the highest bacterial load is found in the large intestine—it is not surprising that higher consumption of processed red meat is associated with an increased risk of colon cancer. Alongside dietary adjustments, including reducing processed red meat and increasing fibre intake, it is essential to take colorectal cancer screening programmes seriously; in the United States, population-based screening has been recommended and widely implemented since the early 2000s, with national guidelines endorsing regular screening for average-risk adults.

According to the IARC classification (2015), processed meat is placed in Group 1 carcinogens (proven carcinogens, alongside substances such as tobacco and asbestos), while red meat is classified as Group 2A (probable carcinogens, comparable to UV-A tanning lamps or certain anabolic steroids).

THE RISKS

The incidence of CRC in the United States is approximately 37 new cases per 100,000 people per year, compared with around 24–30 in the EU. Eastern Europe, the Balkans, and Croatia carry a higher risk, with about 44 new cases per 100,000 people annually.

If you receive stool sample test kits by mail—or notice that your parents have received them—do not throw them away. These tests detect invisible blood in the stool, which may indicate dangerous changes in the intestinal lining. The cause can also be benign, such as internal haemorrhoids, but the only reliable way to clarify this is colonoscopy. This allows the physician to directly visualise any changes, such as polyps, which are often removed immediately and sent for analysis.

If you notice blood in the stool—especially in larger amounts—dark, almost black stools, abdominal pain, or alternating diarrhoea and constipation with or without blood and bloating, you should seek medical attention without delay. In addition to colonoscopy, specific blood markers will also be assessed.

If most of your meals consist of red meat (for example, four times a week or more), it is essential to follow preventive recommendations. While a fully plant-based diet may feel unrealistic for many, the first and most important step is to eliminate processed red meat, such as pâtés and cold cuts.

PRVENTION MEASURMENTS

Five-year survival of CRC in the United States and the EU is around 60–63%, whereas in Croatia it is only about 50–52%. This point is crucial: when CRC is detected at stage I, five-year survival exceeds 90%.

It is also important to stress that detection at this early stage is extremely limited with abdominal ultrasound. On colonoscopy, however, these early changes usually appear as small polyps that can be easily removed. Tumour markers may still be normal in these initial stages. The conclusion is clear: although unpleasant, colonoscopy is the examination that saves lives.

Industrial processed meat products—such as frankfurters, pâtés, salami, bologna-type sausages, deli meats, hot-dog sausages, industrial bacon, and canned meats—are foods that should be avoided or at least strictly limited. In contrast, vegetables that naturally contain nitrates do not pose the same risk. Why? In vegetables such as beetroot, nitrates occur alongside vitamin C, polyphenols, and other protective compounds, preventing their conversion into harmful N-nitroso compounds in the gut.

Many people assume that this risk does not apply to homemade cured meats. However, this depends entirely on the recipe. If curing salt or nitrite salt is added to homemade meat, the risk is essentially the same as with industrially processed products. Regarding intake and quantities, the World Cancer Research Fund (WCRF) recommends avoiding processed meat altogether and limiting red-meat portions to no more than two to three small servings per week (beef, pork, lamb). Poultry and fish are not considered risky, while vegetables have a protective effect, making the overall balance and distribution of meals throughout the week crucial.

In other words, it is not necessary to eliminate meat entirely—but processed meat should be avoided, and other meats consumed thoughtfully and in moderation.

Sooner or later, we all encounter the topic of melatonin—the remarkable compound best known as a supplement used to improve sleep quality and help with falling asleep. In fact, melatonin is the only neurotransmitter secreted by our pineal gland. This small, pea-sized gland is located deep in the center of the brain, behind our eyes which it is connected to.

Based on the sight information, the pineal gland releases the highest amounts of melatonin during the darkest hours of the night ( 1 -5 a.m.). It is therefore easy to understand how artificial lighting and screen exposure at night can confuse the signals it receives. This leads to disrupted melatonin secretion and disturbances of the normal circadian rhythm (the day–night, wake–sleep cycle). But what other effects does this neurohormone have, and what are the benefits of taking it as a supplement?

Melatonin was first observed in 1917 as an unknown compound in the pineal glands of cows. When extracts were applied to frog skin, they caused changes in skin color. It was not until forty years later that an American dermatologist isolated and named melatonin, initially with the idea of using it to treat various skin conditions.

It was already known at that time that melatonin is produced in much higher amounts at night—more than eight times higher. In study participants, the peak secretion occurred between 10 p.m. and 7 a.m., meaning while sleeping and in dark conditions.

In addition to screen exposure, frequent night shifts pose a significant problem. They are associated with an increased risk of heart disease, digestive issues (ranging from IBS to inflammatory bowel disease), sleep disorders, and even a higher incidence of certain cancers. If changing jobs is not possible, night-shift workers are advised to take melatonin supplements in the early morning hours (between 1:00 and 4:00 a.m.) and to compensate with daytime sleep in softly lit conditions—rather than in complete darkness.

Melatonin has also been shown to have very strong antioxidant properties—almost twice as powerful as one of the most well-known antioxidants, vitamin E. It not only promotes the production of antioxidant enzymes that remove free radicals (harmful compounds that damage DNA), but also stimulates immune system cells.

Melatonin in the bloodstream helps reduce chronic inflammation (for example in obesity, metabolic syndrome, and insulin resistance) and prevents the oxidation of LDL, the so-called “bad cholesterol.” As a result, LDL becomes less likely to adhere to blood vessel walls, reducing the formation of atherosclerotic plaques—the most common cause of angina pectoris and heart attacks.

NEUROPROTECTIVE EFFECTS

Through its strong antioxidant action, melatonin plays a particularly important role in protecting the brain, which contains a high density of melatonin receptors. Numerous studies have shown that melatonin supplementation has a protective effect in stroke, reducing the extent of affected brain tissue. In Alzheimer’s disease, melatonin use has been shown to improve continuous nighttime sleep.

Studies have also reported an increase in hippocampal volume—a brain region crucial for learning and memory—after six months of melatonin supplementation. While melatonin shows potential preventive effects in reducing the risk of developing neurological disorders, the most important form of prevention remains regular, high-quality sleep.

MEN’S AND WOMEN’S HEALTH & FERTILITY

Considering that even occasional disruptions of regular sleep can lead to menstrual cycle irregularities, it is not surprising that melatonin is closely linked to women’s health and fertility. Positive effects of melatonin supplementation have been observed in polycystic ovary syndrome (PCOS), where it has been shown to reduce symptoms such as hirsutism (excess facial hair). A 2013 study found that after eight weeks of melatonin use, women with endometriosis experienced a significant reduction in pain.

The role of melatonin in fertility should not be overlooked, and it is often recommended for women experiencing difficulties with conception, either as a standalone supplement or in combination with myo-inositol. Notably, the follicular fluid surrounding the egg cell just before ovulation contains up to three times higher levels of melatonin than blood, and placental cells are also known to secrete increased amounts of melatonin.

In men, in vivo (human) studies have demonstrated improved sperm motility and integrity with melatonin supplementation. After 45 days of use, increased melatonin concentrations were observed in seminal fluid. Acting as a powerful antioxidant, melatonin helps reduce sperm DNA damage, improves sperm function and penetration ability, and overall enhances sperm quality—thereby increasing the chances of conception.

FIGHTING THE BREAST CANCER?

Given its strong antioxidant properties, melatonin quickly became a subject of research as a supportive agent in cancer care. Several studies have linked higher melatonin levels with a stronger immune response against tumors. One study suggested that melatonin therapy may reduce the number of receptors involved in the invasive spread of ovarian cancer. As a potent antioxidant, melatonin enhances the activity of enzymes responsible for DNA repair, which may slow tumor progression and reduce the toxicity of chemotherapy and radiotherapy.

This effect has been associated with fewer side effects when melatonin is used alongside chemotherapy, such as oral inflammation, bone marrow suppression, weakness, and fatigue, while also improving sleep quality. Several well-designed studies have shown a higher incidence of cancer in women who work night shifts over long periods. In one such study, melatonin levels were measured in the urine of nurses frequently exposed to night work; those with lower melatonin levels had a higher risk of developing breast cancer later in life.