Interesting Things About GLP-1 Receptor Agonists

Most of the research on these drugs, over the years, has been performed with an eye to their usefulness in treating Type 2 diabetes. The findings are also, obviously, pertinent to their effects when prescribed for weight loss in non-diabetic patients.

And of course, it is not their effects alone that matter, but what happens when those effects combine with whatever else the patient is already taking? The professional with a prescription pad must be meticulously conscientious in recording a patient’s history, lest something important and potentially threatening slip through the net.

Regarding the currently existing GLP-1 RA meds, there are a few widely recognized contraindications. Except for oral semaglutide, the others are administered by subcutaneous injection. Some concerns do or may apply to all drugs in this class; others are so far known to only be relevant to one of them. Fortunately, many of the potential problems mainly apply to conditions that are relatively quite rare.

A very detailed report originated in 2006 and has been revised 11 times since then, now stating (among other things):

All GLP-1 agonists have been found to cause c-cell tumors in rodent models, but the human relevance has not been determined. All agents except for [two] have a black box warning for risk of thyroid C-cell tumors,

GLP-1 agonists have not been studied in patients with gastroparesis, and all drugs within this class, except for liraglutide and semaglutide, recommend against use in patients with preexisting gastroparesis.

However, their rep is mostly positive:

There is no basis for limiting the duration of treatment for GLP-1 agonists in patients using this medication for chronic weight management if it remains beneficial for weight loss and is not causing intolerable side effects.

Here are some of the caveats and cautions applicable to either the whole class, or various individual drugs. All of them are, of course, contraindicated in patients who are hypersensitive to the particular substance. All should be warned that since the drugs increase the sensation of satiety, it is quite possible that continuing to eat past the point of feeling full can cause nausea and/or vomiting.

Individual drugs are warned against for patients with existing or incipient pancreatitis, gastroparesis or inflammatory bowel disorders, renal disease, or Multiple Endocrine Neoplasia syndrome type 2. Likewise, for those who have a family history of medullary thyroid cancer.

They probably should be avoided for patients who are on tricyclic antidepressants. It should be noted that the GLP-1 receptor agonists, which are therapeutic peptides, could potentially cause the development of drug antibodies.

Another article, titled “Glucagon-like Peptide-1 (GLP-1) Receptor Agonists,” offers a very thorough comparison of the various available meds of this type. For starters, their efficacy and safety “primarily differ by their frequency of administration.” They all delay gastric emptying and increase satiety, and “There is no significant [clinically meaningful] difference in weight loss effect among the agents in the class.”

Here are other details that could be very disappointing, because none of these things match up with what their various manufacturers would have us believe:

Semaglutide is the only GLP-1 receptor agonist that is available as a once-daily oral tablet. Unlike semaglutide injection, the evidence of CV benefit using the oral route has not been definitively established. Compared to placebo, all agents, except albiglutide, significantly reduced weight and increased the risk of hypoglycemia and GI side effects. There were no clinically meaningful differences in weight loss effects, blood pressure reduction, or hypoglycemia risk among the drugs.

Your responses and feedback are welcome!

Source: “Drug Use Criteria: Glucagon-Like Peptide 1 Receptor Agonists,”, October 2022
Source: “Compare and Contrast the Glucagon-Like Peptide-1 Receptor Agonists (GLP1RAs),”, 03/27/23
Source: “Glucagon-like Peptide-1 (GLP-1) Receptor Agonists,”, 04/11/22
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About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
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Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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