Bodybuilding peptides are a type of drug that’s often portrayed as a safe, legal alternative to anabolic steroids.

In recent years, their sales have surged, mainly thanks to supplement companies’ claims that they boost fat loss and muscle gain safely and naturally.

Is this true?

Are peptides a kind of “steroids lite?” 

Half the gains but none of the nasty side effects and thorny legal concerns?

Get an evidence-based answer in this article.

What Are Bodybuilding Peptides?

The term “peptide” refers to any molecule that consists of between 2 and 50 amino acids chemically linked by peptide bonds.

Peptides exist naturally in the body and animal- and plant-based protein sources such as meat, fish, dairy, eggs, milk, soy, oats, pulses, and lentils. They can also be synthesized artificially in a lab.

When people refer to “bodybuilding peptides,” they’re typically referring to a powdered or injectable type of peptide used to stimulate human growth hormone (HGH) secretion, also known as a growth hormone secretagogue (GHS).

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What Are the Benefits of Peptides for Bodybuilding

Research shows that peptides increase human growth hormone levels.

Boosting HGH is a boon for bodybuilders because it causes fat “mobilization,” which means it helps your body release the fatty acids stored in fat cells, making it easier to burn fat and preserve muscle while cutting.

HGH also promotes the release of insulin-like growth factor 1 (IGF-1), which triggers muscle growth and further encourages fat mobilization.

Thus, the theory is that taking peptides will help you gain muscle and lose fat. And since it’s legal to purchase peptides (thanks to a labeling loophole, more on this in a moment) and they’re generally considered safe, they’re seen as a more health conscious, above-board alternative to steroids like trenbolone, winstrol, and testosterone. 

That’s assuming they work, though, which is debatable. 

While there’s a solid mechanistic argument for how peptides can help improve body composition, there’s little hard evidence that they work the way many bodybuilders hope.

For example, research conducted by scientists at the University of Chile, Schneider Children’s Medical Center of Israel, and the University of Washington shows that peptides are effective at increasing HGH and IGF-1 levels in short prepubescent children. Although this is good evidence that peptides can help little kids grow as tall as their peers, it’s not compelling evidence that it’ll help a 35-year old man lose fat and build muscle. 

Other studies show that peptides may produce beneficial effects among the elderly and infirm. 

For instance, studies conducted by scientists at the University of Technology Sydney, Massachusetts General Hospital Cancer Center, and Kyoto Prefectural University of Medicine show that lung cancer patients who take the peptide anamorelin may gain weight slightly more effectively than patients who don’t.

Likewise, studies show that using peptides increases HGH and IGF-1 in elderly people recovering from bone fractures.

Again, though, it’s difficult to see how any of these results apply to healthy young people looking to boost fat loss and muscle growth.

Other studies show that peptides may help obese people and those affected by Prader-Willi syndrome (a genetic disorder that often leads to obesity and type 2 diabetes in adulthood) improve their body composition. 

However, these results aren’t applicable to non-obese individuals since obese people tend to have impaired growth hormone secretion, which means their response to treatment isn’t always typical of what you see with healthy-weight people.

Only a few studies have looked at the effect of peptide use in healthy lean people. While the results of these studies appear favorable at first blush, they tend to be “underpowered” (involve too few participants) or marred by methodological missteps that make their results impossible to extrapolate to the average gymgoer.

For example, one study conducted by scientists at Kobe University School of Medicine found that injecting peptides raised HGH and IGF-1 in healthy men. But this study only involved 6 participants, only tracked the change in hormone levels for 3 hours, and didn’t involve an exercise regimen or examine how raising these hormone levels affected body composition.

In another study conducted by scientists at Merck Research Laboratories, participants who supplemented with a single daily dose of the peptide MK-677 didn’t lose muscle while dieting (which is what usually happens). However, the diets lasted just 7 days, and the study only involved 8 participants, none of whom consumed adequate protein or lifted weights.

Eating enough protein and lifting weights effectively preserves muscle during a diet, and since any bodybuilder worth their salt does both of these things routinely, it’s difficult to see how taking peptides would offer any further benefit. And if you’re fairly new to weightlifting, sufficient protein and proper strength training can even help you gain muscle and lose fat at the same time.

Finally, a study published in Annals of Internal Medicine found that taking a single daily dose of MK-677 was enough to raise HGH and IGF-1 levels in healthy elderly adults, prevent sarcopenia (age-related muscle loss), and decrease visceral fat over a 2-year period.

These findings are undeniably promising, but they tell us nothing about how peptides affect young people who exercise regularly.

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Why You Shouldn’t Use Peptides for Gaining Muscle and Losing Fat

The main reason you should avoid bodybuilding peptides is that there’s no evidence that they help healthy people who regularly lift weights lose fat and gain muscle.

While there are a few theoretical arguments for how they might do this, you’d have to be gonzo to risk your health by taking them before there’s long-term evidence they’re safe and effective.

Currently, there’s no data on the long-term health effects of taking peptides. Although most studies show that taking peptides for several weeks or months is safe, we don’t know if there might be negative side effects that only rear their head years down the road (like cancer, heart disease, and so on).  

For instance, one study in elderly patients had to be cut short because the researchers were concerned that the peptides the participants were using increased the rate of congestive heart failure (four patients taking peptides developed congestive heart failure during the study).

What’s more, many studies report unwanted side effects from taking peptides including increased sweating, flushing, or sensations of warmth, muscle pain, fluid retention, disturbed sleep, and increases in cortisol and prolactin.

Interestingly, two other common side effects are increased appetite and decreased insulin sensitivity, both of which could potentially undermine your efforts to lose weight. 

The legality of peptides is also sketchy.

The law prohibits the sale of peptides as a dietary supplement but permits their sale as “research chemicals” or “not for human use.”

In other words, the only people who are supposed to buy peptides are scientists looking to learn more about how they work and whether or not they have worthwhile therapeutic uses.

Of course, the majority of peptides you see for sale online never wind up in a lab. Instead, they find their way into bodybuilders, athletes, and fitness buffs who want to get leaner and more jacked.

This opens the doors to all kinds of monkeyshines. For example, shady supplement companies may contaminate peptides with other chemicals because they’re not obliged to maintain rigorous quality standards, or mix them with weaker and sometimes harmful substances and mislabel them to increase profits.

The bottom line is the peptides market is a lawless free-for-all, which makes buying and taking them a gamble you shouldn’t risk if you take your health seriously.

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FAQ #1: What are the best peptides for muscle growth?

Many supplement companies claim they sell the “best peptides for bodybuilding,” but this is marketing bluster.

There’s no good evidence that peptides help young, healthy people gain muscle.

As such, there’s no such thing as “the best peptides for muscle growth.”

FAQ #2: What are the best peptides for fat loss?

The internet is teeming with companies claiming they sell fat-loss peptides, but this is bunk.

There’s no good evidence that peptides help young, healthy people lose fat.

As such, there’s no such thing as “the best peptides for fat loss.”

FAQ #3: Are peptides safe?

Most evidence suggests peptides are safe to use over the short term, but we have little data about how safe they are over the long term.

“Most evidence” doesn’t mean “all,” of course. 

One study in elderly patients had to be cut short because the researchers were concerned that the peptides the participants were using increased the rate of congestive heart failure (four patients taking peptides developed congestive heart failure during the study).

FAQ #4: Should I buy bodybuilding peptides?


There’s no good evidence that peptides can help you improve your body composition.

If you want to take muscle-building supplements that are backed by well-designed, peer-reviewed research, here’s what I recommend:

  • 0.8-to-1.2 grams of protein per pound of body weight per day. This provides your body with the “building blocks” it needs to build and repair muscle tissue and help you recover from your workouts. If you want a clean, convenient, and delicious source of protein, try Whey+ or Casein+.
  • 3-to-5 grams of creatine per day. This will boost muscle and strength gain, improve anaerobic endurance, and reduce muscle damage and soreness from your pull workouts. If you want a 100% natural source of creatine that also includes two other ingredients that will help boost muscle growth and improve recovery, try Recharge.
  • One serving of Pulse per day. Pulse is a 100% natural pre-workout drink that enhances energy, mood, and focus; increases strength and endurance; and reduces fatigue. You can also get Pulse with caffeine or without.

And here are the best supplements that are proven to boost fat loss:

  • 3-to-6 mg of caffeine per kilogram of body weight per day. This will raise the number of calories you burn and also increases strength, muscle endurance, and anaerobic performance. If you want a clean, delicious source of caffeine that also contains five other ingredients that will boost your workout performance, try Pulse.
  • 0.1-to-0.2 milligrams of yohimbine per kilogram of body weight before fasted workouts (if you choose to train fasted). This increases fat loss when used in conjunction with fasted training, and is particularly helpful with losing “stubborn” fat. If you want a 100% natural source of yohimbine that also contains two other ingredients that will help you lose fat faster, preserve muscle, and maintain training intensity and mental sharpness, try Forge.
  • One serving of Phoenix per day. Phoenix is a 100% natural fat burner that speeds up your metabolism, enhances fat burning, and reduces hunger and cravings. You can also get Phoenix with caffeine or without.

(And if you’d like even more specific advice about which supplements you should take to reach your health and fitness goals, take the Legion Supplement Finder Quiz, and in less than a minute, you’ll know exactly what supplements are right for you. Click here to check it out.)

No and yes.

It’s illegal to sell peptides as a dietary supplement, but you can sell them as “research chemicals,” “for research use only,” or “not for human use.”

Thus, thanks to a legal labeling loophole, it’s de facto legal to purchase them for personal consumption but frowned upon de jure.  

+ Scientific References