Illegal for the professional sportspeople among us – here's looking at you Lance Armstrong – they are (mostly) legal and a huge growth area (ahem) for people like us.

All of us.

From gym junkies using them in place of steroids or for injury recovery, to the Botox brigade using them for fat loss, tanning or anti-ageing, to those looking to address anxiety issues or sexual dysfunction, there is a peptide out there for you.

All of you, so the exploding peptide industry promises, all sparkly smiles and injected tans.

The big promises are making their mark. Literally, with people paying big bucks (about $4000 for a 10-week course) to inject themselves with peptides.

Yep, to bypass the digestion process, where peptides (amino acids that are also referred to as "small proteins") are broken down, they are either applied to the skin as a cream or injected using a painless (so I'm told), disposable insulin needle.

Since opening in September 2014, Sydney-based Peptides Clinic has grown to employ 50 people and boasts 17,000 customers.

Are they all onto the magic bullet that peptides appear to be?

"They're not the magic answer to everything," admits Dr John Hart, medical director at Peptides Clinics.

The hormone doctor says he was converted after trying them himself, following his 50th birthday and suffering low libido, stress, a lack of sleep and an expanding belly.

"I've done a lot to turn that around," Hart says, "not just peptides, but I've turned my body back 20 years ... peptides are part of the story."

Part of the story because as we age, our natural testosterone and repair processes slow down. Peptides stimulate these processes again.

"Peptides enhance the body's natural responses," explains Robert Robergs, a professor of exercise physiology and biochemistry at Charles Sturt University.

It is in this way that peptides have become a popular alternative to steroids among athletes, both amateur and professional.

Steroids directly affect the receptor that makes muscles, but they also come with the not-so-nice side effects of testosterone like acne, oily skin and random hair distribution.

Peptides, on the other hand, simply stimulate the release of our natural human growth hormone which, in adulthood, repairs tissue and helps muscle growth, so you get the benefits but not the sticky side effects.

Trainer to the stars and F45 founder Luke Istomin says peptides are increasingly popular in the fitness industry.

"I have different friends who use peptides and others who use steroids, and the difference in body composition, skin reactions, sexual drive and mental aptitude is hugely different between the peptide users and the steroid users," he says. 

"Peptides do not alter your hormones like a steroid, so the immediate effects, and side effects that steroids give, are vastly different."

Robergs agrees that the excitement around peptides is there for a reason.

"There's quite a bit of dialogue about peptides to improve recovery among people who aren't restrained by sports regulation," he says.

Those regulations are restraining research into their effects though, he says.

"Academics like myself are discouraged from researching them because they're an illicit practice [in sport]," he says, adding that instead of the medical industry, "right now, the business model, the money-making model, is in charge". 

Robergs questions who is developing the standards, noting that as far as research into standards goes, "not a lot has been done".

The lack of testing means there is cause for concern, particularly when so many people are lured by stories of sensational effects.

But there are horror stories about peptide use, too.

The problem, as with many things, is that there are as many variables in quality and safety as there are peptides.

One of the main concerns raised is that the promotion of cell growth can also cause cancer cell growth.

"There are potential concerns with the long-term use of any agent that promotes cell growth," Sports physician Dr Peter Larkins has said.

"There are not lots of clinical trials. A lot of the information on them is anecdotal and testimonial, not scientific ...

"Why use a product with unknown side effects when you're a healthy person?"

"Right now, it's a speculative concern," says Robergs, "it's just unknown, which is in itself a concern."

Dr Steve Hambleton, president of the Australian Medical Association, agrees that there are more marketing-driven claims than results-driven claims currently. 

"If you're already a healthy adult it's not really going to do much. The impact is really unclear," he told Elle earlier this year. "Peptides are very important in early growth in childhood, but it's dubious to make all these claims. 

"The best solution for anti-ageing is the same one we've been saying for years: stop smoking, limit your alcohol, exercise more and eat a balanced diet. If peptides sounds too good to be true, they probably are."

Istomin, on the other hand, has seen the results and sees no problem if they're not abused.

"They haven't been shown to have too many side effects for people who haven't been predisposed to any cancers or health issues," he says.  "If you've had a clean bill of health prior to using them, and they are from a reputable company that has developed peptides for human consumption, then I personally don't see the harm in it. It's science at its cutting-edge finest."

Hart agrees.

"I think we have to be careful with everything," he says.

"You can kill yourself with too much oxygen or water ... but there's a sweet spot where you can keep your levels where they were in their 20s. We have to be careful about throwing out the baby with the bathwater." 

Whether peptides are science at its cutting edge-finest or too good to be true, it's too early to tell. 

In the meantime, for the fitness and cosmetic curious, the jury might be out but peptides are well and truly in.