A new experimental GLP-1 medication is attracting attention and has already picked up the nickname the ‘Godzilla’ of weight loss drugs. But anyone hoping to try it will need to be patient, because it is not currently available to the public. Even so, some people taking part in trials have shared what the experience has been like, including the side effects they say can come with it.
The drug is called retatrutide, often shortened to reta. It is described as a triple agonist because it targets three hormone receptors involved in appetite and metabolism at the same time: GIP, GLP-1, and glucagon. Lilly says the drug remains investigational and is only available through its clinical trials, and in 2026 the company also noted that the term “GLP-3” is an informal label rather than a scientific classification.
Eli Lilly is currently evaluating retatrutide in Phase 3 clinical trials covering a wide range of conditions. On its website, the company says it is being studied for obesity, type 2 diabetes, knee osteoarthritis pain, moderate-to-severe obstructive sleep apnea (OSA), chronic low back pain, cardiovascular and renal outcomes, and metabolic dysfunction-associated steatotic liver disease (MASLD). Lilly says its initial Phase 3 program has now generated topline results in obesity, type 2 diabetes, and knee osteoarthritis, with more readouts still expected.
At the time of writing, the treatment has not been approved by any regulatory authority. Lilly has also warned people not to use products “claiming to be retatrutide outside of a Lilly-sponsored clinical trial”.
People who say they are currently testing the weight-loss drug have been discussing their experiences in a Reddit thread, where a number of users described symptoms they noticed after taking it.
“Fatigue, nausea, insomnia, GERD, dry mouth,”
One participant listed those issues, which closely resemble side effects already associated with GLP-1 medications like Ozempic.
Others also described stomach-related problems, something commonly reported with drugs in the same category.
“First few days after my shot I get severe diarrhea, gas and bloating with the occasional nausea. I have been living off of Gatorade and gas x maximum relief. I’m only on my first month about to start my second so 5th shot today. Oh and the burps! The sulfur burps are repulsive,”
One user said those symptoms followed their injections.
“First 2mg dose basically gave me food poisoning symptoms for 2 days. Diarrhea and nausea after eating. Next shot will be 1mg and I’ll see how I feel from there.”
Another person compared their first dose to food poisoning.
When someone asked how long those effects lasted, the same poster added:
“2 days of the heavy nausea and diarrhea for one 3-4. I’m on 1 mg now. It’s much better.”
While fatigue was mentioned by some users, others focused on sleep disruption. One person asked whether anyone else had experienced insomnia while using the drug.
“The insomnia is the one that got me. I checked the side effects several times and this was not listed. I could lay awake all night on 10mg.”
That commenter said sleeplessness had been the most difficult issue for them.
Another user said they “couldn’t sleep past 3am each day” during the first few months, while someone else reported experiencing cramping after starting the treatment.
So far, the research shared by Lilly suggests the most frequently seen side effects are still digestive, including nausea, diarrhea, vomiting, constipation and abdominal pain. In the company’s Phase 3 obesity and diabetes studies, those adverse events tended to show up mainly during dose escalation, and Lilly also reported dysesthesia, or unusual skin sensations, in some participants.
The company’s newest Phase 3 results have also shown how powerful the drug may be if it eventually reaches the market. In May 2026, Lilly said retatrutide met the main goals of its TRIUMPH-1 obesity study, and in March 2026 it reported positive topline results in type 2 diabetes. In both cases, the drug produced substantial weight loss, with side effects broadly similar to those seen with other incretin-based medicines.
That means the stories from trial users about nausea, diarrhea, fatigue, and sleep disruption are happening against the backdrop of a drug that is still being tested, not yet approved, and still being refined in the clinic.