Are Peptides Steroids, Is There A Difference?

We get many inquiries from people asking us all sorts of questions about peptides; one that keeps popping up is the similarity with steroids.

So, let’s first set things straight – peptides are not steroids. There are differences in structure (since peptides are peptide-derived hormones while steroids are lipid-derived) and in the mechanism of action (since steroids increase hormone levels unnaturally and peptides stimulate natural hormone secretion).

Types Of Hormones In The Human Body

Roughly speaking, hormones in the human body are divided into three distinct categories:

1. Peptide hormones – peptide hormones are basically hormones made up of small amino acid chains
2. Lipid-derived – these are the hormones derived from lipids (fats)
3. Amino acid-derived – these are hormones derived from small amino acids

Peptide Hormones

As we already said, peptide hormones are built up of chains of amino acids (polypeptide chains) and are introduced into the blood in the posterior pituitary gland. Peptide hormones are soluble in water and, of course, insoluble in lipids.

These hormones are stored within the cells, which only release them in response to stimuli, and their receptors are found on the surface of the target cells.

Lipid-Derived Hormones

Most lipid-derived hormones are derived from cholesterol, and the primary class of these lipid hormones is steroids. The most renowned steroid hormones are testosterone – androgen or male hormone, and estradiol, estrogen or female hormone, both being released by male and female reproductive organs. On the other hand, we also have those released by the adrenal glands, such as cortisol and aldosterone.

Lipid-derived hormones are insoluble in water and get carried by transport proteins found in our blood. These qualities result in a much longer half-life of 60-90 minus, as opposed to peptide or amino acid-derived hormones.

Amino Acid-Derived Hormones

These hormones are primarily small molecules derived from tyrosine and tryptophan amino acids. Some of the more renowned amino acid hormones are epinephrine, norepinephrine, and thyroxine, which are synthesized in the medulla of the adrenal glands and thyroid gland.

Differences Between Peptide And Lipid-Based Hormones

Since we’ll only talk about the differences between peptides and steroids, we won’t talk much about the amino acid-derived hormones. 

We already saw differences in chemical structure, solubility, and the method of action. 

Chemical structure – peptide hormones are built up of small amino acid chains, while the precursor for steroids is cholesterol. This leads to significant differences in:

1. Structure – amino acids in peptides are held together by peptide bonds, which is why they might vary in length and overall shape. In contrast, steroids have a distinct four-ring structure that derives from cholesterol.
2. Function – peptides have a diverse portfolio of actions within our body, acting as hormones, enzymes, neurotransmitters, etc. This allows them to also influence different processes within our body, such as growth, immune system response, and metabolism, among others. Steroids, conversely, serve as signaling molecules that primarily modulate gene expression. 
3. Metabolism – peptides are typically broken down by specific enzymes that regulate their levels and keep our body in balance. Breaking down steroids is a different story involving multiple steps, several other enzymes, and regulation pathways.

Solubility – peptides are water, while steroids are lipid soluble. This translates into differences in:

1. Absorption – since peptides are water soluble, they can get easily absorbed into the bloodstream, administered orally or via injections. While traveling the bloodstream, they interact with the water-soluble receptors on the cell surfaces. Because steroids are lipid soluble, they penetrate the cell membrane easily, allowing them to interact directly with the cell.
2. Receptor binding – peptides typically bind to the surface cellular receptors where they signal and regulate various functions. Steroids penetrate the cell, bind to the intracellular receptors, and directly modulate gene expression and protein synthesis.
3. Application – Though it might not seem important to consider, solubility characteristics play a crucial role in pharmaceutical formulations and govern the means of application. Being water soluble, peptides are most suitable to be injected and taken orally, while steroids can be taken orally, injected, or even applied topically.

Mechanism of action – mechanism of action refers to their effect on the endocrine system and overall hormone levels in the body:

• Peptides – from what we know so far, it’s evident that peptides act as signaling molecules within the body that stimulate the release of certain hormones from various glands around our body. What’s typical about peptides is they act within the body’s natural regulatory mechanisms and eventually balance out.
• Steroids – steroids are completely different as they directly introduce hormones into our body through a synthetic compound. Even though steroids also increase levels of hormones within our body, they do not follow the body’s regulatory mechanisms and even disrupt the natural balance. 

Is Testosterone a Peptide?

After all we’ve said so far, we can safely say testosterone is not a peptide – it’s a steroid, a lipid-based hormone with a cholesterol base. Peptides are made up of amino acids, held together by peptide bonds, water-soluble, and work within the natural limits of our body. 

We saw earlier that lipid-based hormones are not water soluble, penetrate the cell, work with the receptors within it, and bring hormone levels outside of the natural limits of our body; unlike peptides, which are water soluble, bind to the receptors found on the cell’s outside surface, and only stimulate the hormone secretion but our body can regulate these levels and bring the body back into homeostasis.

Are Peptides Safer Than Steroids?

When discussing any artificial substance we introduce into our body, we need to be aware of the potential side effects and consequences. Of course, both peptides and steroids can bring about these adverse effects, depending on the dosage.

Of course, peptides are smaller and composed of amino acids, and they ultimately “only” signal the body to increase the secretion of certain hormones. For this reason, we consider peptides to be a safer option as opposed to steroids generally.

Steroids, especially anabolic, increase hormone levels in the body to unnatural values, which can bring about a whole host of negative side effects. This is why steroids are generally considered a more dangerous option, but athletes (especially bodybuilders) continue to use them to improve their athletic abilities.

Can Peptides Affect Testosterone?

There hasn’t been much research yet, but some laboratory experiments suggest that specific peptides affect testosterone levels. Among other things, peptides affect the endocrine system and hormone pathways, which, in turn, affects testosterone levels.