Millions of people across the globe are currently turning to synthetic GLP-1 receptor agonists to manage their obesity. Humans tend to be sold on “easy-fix” approaches to solving the problems they have inflicted upon themselves. Having been swamped with media coverage, and paid celebrity endorsements, demand for this new category of weight-loss drugs has ballooned. 

The reality of obesity now has a bizarre financial side. With the promise of a quick-fix, vast numbers of people, having paid huge amounts of money for the food that has made them obese, are now paying vast quantities of cash reverse that harm.

Even more alarmingly, a new category of people seems to be emerging: those who are no longer careful about how much they eat because they have convinced themselves that synthetic GLP-1 drugs can solve the problem. They have given themselves a licence to binge.

That is just the start of the emerging tsunami of serious health concerns. Whilst early clinical worries focused on the side effects like mild nausea or temporary digestive discomfort, a far more serious reality is surfacing.

Patients using GLP-1 receptor agonists commonly report gastrointestinal effects and lose lean mass along with fat. Less often they experience delayed gastric emptying severe enough to cause gastroparesis or ileus. Rodent thyroid findings prompted a boxed warning, while human cancer risk remains unproven. Effects on appetite and reward pathways are expected from the drugs’ action in the brain; robust evidence of widespread unexpected neurological or psychiatric harm is still mixed.

Many people who are using synthetic GLP-1s are reported to be continuing to eat unhealthily, and as a result the drugs are being prescribed long-term, meaning, potentially for life. That is alarming. Why? Because the actual long-term impact on the body of synthetic GLP-1s is unknown. Well, unknown for the time being, but not for long; the permanent users of the drugs are perhaps, unknowingly participating in a  real-life experiment; many of the previously unknown harms of new medications only emerge after large number of members of the public have been consuming the drugs. 

How GLP-1s work in body and brain

Natural GLP-1 is a gut hormone released by intestinal L-cells after a meal. A receptor agonist is a drug that binds that same receptor and turns it on.

In a healthy person the hormone acts in three places at once. It tells the pancreas to release insulin only when blood glucose is already high. It slows the emptying of the stomach into the small intestine. It also reaches brain receptors that signal fullness.

The body’s own GLP-1 is broken down within one or two minutes. That short life is unlikely to be an accident. Synthetic GLP-1 receptor agonists are built to resist the enzymes that would normally clear them, so they can linger for up to a week and at levels far above ordinary human physiology. That gap is one reason longer-term effects are still unknown.

By driving GLP-1 receptors across several organ systems, the drugs impose a standing sense of having already eaten enough. In the brain’s reward circuits they also dampen dopamine signalling. For many people that quiets the loop of wanting food. The cost is that dopamine also shapes motivation, anticipation and pleasure. Chemicals that lean on those pathways are unlikely to touch appetite alone, and the wider effects are still being learned in real time.

The known short-term risks and harms

Digestive distress and nutrient deprivation

The most widely reported acute side effects of synthetic GLP-1 medications occur within the digestive system. Clinical trial data has indicated that up to 70% of users experience significant digestive symptoms during initial doses. The reported symptoms include: 

• Persistent nausea and vomiting: Delayed gastric emptying and stimulation of brainstem nausea centres cause these symptoms.
• Reflux, heartburn and burping: Food remaining in the stomach for longer increases acid release and relaxes the lower oesophageal sphincter.
• Diarrhoea or severe constipation: Disrupted gut motility and altered water absorption in the large intestine produce these changes.

While these symptoms have been conveniently dismissed as temporary “adjustment costs”, they come at a heavy bodily price. Prolonged nausea stops a person from eating enough food. That in turn causes their body to starve and break down its own tissues for energy. It is known that prolonged under-nutrition can damage the heart.

The hidden harms

Beyond digestive distress there are several far more serious, structural health consequences that are frequently overlooked during routine prescription of synthetic GLP-1s.

• The loss of lean muscle and bone density: Unlike ordinary dieting, where only a fraction of lost weight is muscle, studies report that up to 40% of weight lost on synthetic GLP-1s can be muscle rather than fat, with knock-on harms to bone density, strength, stability and immune function.
• Stomach paralysis and bowel obstruction: These drugs slow gut transit by design, and in some people the stomach stops emptying, so food can rot, cause severe vomiting and malnutrition, form hardened masses, and prompt regulator warnings about obstruction and bowel paralysis.
• Thyroid concerns and pancreatic inflammation: Animal studies found thyroid tumours in rats and people have been reported with severe pancreatic swelling, so health agencies require strong warnings while human thyroid risk is still being studied.
• Adverse interactions with several bodily systems: Resting heart rate can rise by 2–5 beats per minute, rapid weight loss can trigger gallstones and gallbladder swelling, and altered blood flow near the optic nerve can cause a rare form of sudden vision loss.

Chemical interaction risks

Taking GLP-1 drugs with other medicines can be risky. They slow digestion, so the body absorbs swallowed drugs differently.

Medicines that need a tight dose range, such as blood thinners and seizure treatments, can then spike or fade. Birth control pills can fail if the stomach empties slowly or if vomiting and diarrhoea stop the hormones getting through. Fast-acting painkillers, antibiotics and emergency drugs may sit in the stomach and take far longer to work.

The same delay matters before surgery. Food can remain after a normal fast, which raises the chance of inhaling stomach contents under anaesthetic. Mixed with insulin or other diabetes drugs, GLP-1 treatment can also drive blood sugar dangerously low. Alcohol and other nervous-system depressants may act in odd ways because the gut handles them more slowly.

The psychological risks of GLP-1s

Our bodies and minds impact each other constantly. What are the known and likely mental health impacts of GLP-1s?  Chemical dampening of appetite causes several apparently under-reported psychological risks.

GLP-1s do more than just stop hunger. They lower dopamine in the brain’s pleasure centres. Dopamine is a chemical that helps you feel good. Unsurprisingly, then, there have been reports of people feeling a general sense of numbness on GLP-1s. They report not enjoying things they used to love, such as hobbies, physical intimacy, social time, and creative work. 

Many people use food to cope with stress, worry, trauma, or loneliness. That is commonly called comfort eating.  Synthetic GLP-1s take away the comfort in food. I have yet to see any clinic equipping obese people with new, healthier ways to cope with their emotions prior to starting synthetic GLP-1s. Without a new way to cope, people could feel anxious, low, or emotionally lost. That is, assuming they are not one of those for whom synthetic GLP-1s kills joy.

The fast physical changes caused by synthetic GLP-1s could make worse anyone suffering from body dysmorphia or harmful eating habits. Instead of learning a natural, healthy way to manage their food intake, patients rely totally on an expensive chemical. If they miss a dose or if the medicine runs out, that can lead to panic or severe anxiety

The unknown future harms of synthetic GLP-1s

Synthetic GLP-1 receptor agonists were originally designed to manage type 2 diabetes at lower doses. Since then, there has been widespread, high-dose adoption purely for weight loss purposes. The most worrying part of mass synthetic GLP-1 use, is the huge number of long-term unknown health consequences.

• Long-term damage: No datasets cover cardiovascular, neurological or metabolic outcomes after five to ten years of continuous high-dose use, so we still do not know who is safe.
• The synthetic GLP-1 doom loop: Most people regain about two thirds of the lost weight within a year, often as fat after muscle loss, leaving a higher body fat share and a slower metabolism.
• Multi-generational impacts: Effects on bone growth, organ development and fertility in adolescents and women of childbearing age remain unstudied, so later harm cannot yet be ruled out.

Our bodies adjust to their environment, in almost every conceivable way. It is not known whether or how much our GLP-1 receptors adjust over time to regular, long-term doses of synthetic GLP-1s.

Regulatory blind-spot and limitations

Most countries have a pharmaceutical safety regulator of some kind. Even the best agencies have potentially lethal limitations. We won’t go through the long list of drugs that were approved by the regulators in G7 countries that were lethal. Some of the reasons for those regulatory failures include the following. 

• Drug trial duration: Clinical trials run for 1 to 4 years. For obvious economic reasons, regulatory bodies cannot delay approval of drugs for 20 years to observe late-life outcomes, of long-term use, before granting market access.
• Possibly lethal combinations: There are approximately 5,000 active ingredient drugs available world-wide. Testing the safety of synthetic GLP-1s with every possible combination of drugs, supplements and lifestyle habits, with a one to four year period is simply not possible.
• Lethal co-morbidity combinations: Typically, drug trials for safety use volunteers who have no other illnesses, no co-morbidities. That means that regulators have few if any ways of evaluating the efficacy or safety of new drugs for people who have other illnesses. 
• Environment and lifestyle variation: Human diets vary across the globe, as do levels and the precise nature of environmental chemicals. Testing how synthetic GLP-1s interact with, for example, all of the many pesticides to which people can be exposed, is simply not possible. 
• Genetic effects blind spot: There is a universal inability to test synthetic GLP-1s against every possible human genetic variation. With 8.3bn people on planet earth, it is almost certain that synthetic GLP-1s have never been tested against your gene profile. Here are some of the known risks that seem to have emerged.

Some people carry gene variants in liver enzymes or in the GLP-1 receptor that can over-activate the pathway and lead to unusual toxicity or organ injury. Others have variants linked to low muscle density or weak muscle protein synthesis, and they may lose muscle more severely and with less chance of recovery.

Differences in dopamine transporter genes or receptor density may also matter. In those cases the drugs have been linked to sharp drops in mood or a flattening of pleasure. Hidden RET mutations and MEN2 syndromes already raise the risk of a particular thyroid cancer, which is why those conditions sit on the product warnings.

Consider protecting your health if on synthetic GLP-1s

If you choose to use synthetic GLP-1 medication under clinical supervision, of course, it may be wise to consider the following steps with your physician in order to counteract the inherent risks. 

• Resistance training: Regular weight training can limit the muscle loss that often comes with rapid weight reduction and help protect the resting metabolic rate that muscle supports.
• Increasing protein intake: A usual safe intake is about 0.8 g per kg of body weight a day, and many people who lift raise that target to about 1.6 g per kg.
• Protecting your digestive system: Discuss with your doctor a daily intake of about 25 to 30 grams of soluble fibre from oats, chia or psyllium, to keep gut transit regular and stools soft.
• Maintaining hydration and electrolyte levels: Smaller meals supply less water than before, so many people need about 2.5 to 3.5 litres of fluid a day to replace that loss.
• Adopting non-food emotional coping strategies: Plan how you will protect your mood if food no longer lifts it, and use practical well-being tips such as those on psychreg.org.
• Reaching a healthy weight without synthetic GLP-1s: Excess weight often tracks beliefs and daily habits, so changing those in ordinary ways may avoid both the known harms and the long-term unknowns of these drugs.

Dr Nigel MacLennan is the author of The Belief Diet.