Dr. Mike Israetel of Renaissance Periodization recently released a video tackling one of the most common questions he gets from lifters and fitness enthusiasts: Do peptides actually grow muscle? His answer challenges the growing belief that peptides are a shortcut to rapid muscle gains.
He opened with an assessment of the hype surrounding these. “When people ask the question of what peptides do I take to grow muscle, the answer is there are no peptides that grow muscle,” he said.
Israetel added that if such a powerful muscle-building peptide truly existed, the evidence would already be obvious in elite bodybuilding circles. “If there were very powerful muscle-growing peptides around, almost every enhanced bodybuilder would probably know about it by now,” he explained.
To clarify the science, Israetel first defined what peptides actually are. He described them as short chains of amino acids, typically fewer than 50, that primarily act as signaling molecules in the body.
Many well-known hormones fall into this category, including insulin and GLP-1. Synthetic peptides, he noted, are engineered versions of these natural compo unds, often modified to last longer in the body or interact more strongly with specific receptors.
From there, he outlined five major categories of peptides currently circulating in the fitness and medical world. The first group includes modern weight-loss treatments such as semaglutide and tirzepatide.
While he praised their effectiveness, he emphasized their limitations for muscle building. “They are amazing for health and weight loss,” he said, “but they do not have any anabolic muscle-growing effects.”
The second category consists of recovery-focused peptides like BPC-157 and TB-500. These are often marketed as healing accelerators, but Israetel said the evidence for muscle growth remains weak.
According to him, research results are mixed, and so far they show “seemingly no muscle growth effects.”
A third group includes so-called exercise mimetics, which are designed to mimic the physiological effects of training. Israetel expressed particular concern about this category, warning that they are still poorly studied.
He noted that some evidence suggests they may even interfere with muscle-building pathways, describing them as “very underresearched for safety and effectiveness.”
The fourth category involves growth hormone secretagogues, which stimulate the body to release more growth hormone. Israetel described these as supportive rather than transformative tools.
According to him, they function as “permissive anabolics,” meaning they can create favorable conditions for muscle growth but are not powerful drivers of it on their own.
Finally, he discussed IGF-1 modulators, another class often associated with muscle development. Despite their reputation, Israetel argued that their real-world impact is limited and comes with notable risks.
He said they “don’t have massive anabolic drive in the real world,” while still carrying the potential for significant side effects.
When addressing safety, Israetel drew a sharp distinction between different peptide categories. He was particularly optimistic about the modern weight-loss treatments, which he referred to collectively as the “tides,” including semaglutide and tirzepatide.
“They are incredibly safe,” he said, adding that when used properly alongside good nutrition, “they are technically safer to take than not to take.”
However, his tone shifted when discussing recovery peptides such as BPC-157. While not claiming they directly cause cancer, he emphasized that the long-term risks are still unclear.
“There are mechanistic reasons to suspect that long-term risks from high dosing can include increases in cancer rates,” he explained. He clarified the nuance carefully: “No, these d**gs do not cause cancer, but we can’t yet rule out that they don’t help it along if it’s already on its way.”
Israetel also warned about the practical risks of obtaining these substances. Many peptides are not available through standard medical channels and instead come from unregulated suppliers.
“Many of these you have to get through gray market online labs,” he said. “Just know that you’re rolling the dice when you buy through online peptide shops.”
Looking ahead, he expressed more excitement about a different frontier in performance and health science, oral small molecule drugs rather than peptides themselves. He believes the next wave of breakthroughs may arrive sooner than many expect.
“I think we’re just a few years away from oral small molecule drugs for all kinds of things: physique, health, and even psychology-related benefits,” he said.
He closed with a simple but cautionary message for anyone considering peptides. “If you take peptides, know the risks. Have a goal,” Israetel advised. “Don’t just get caught in the hype just yet.”
