Best Peptides for Immunity: The 3-Peptide Stack I’ve Run Since COVID

Everyone around me is getting sick right now.

And I mean everyone.

My son’s school sent three emails last week about flu outbreaks. Half the guys at my gym are out. I was at the grocery store and the checkout lady was coughing into her elbow like she was auditioning for a disaster movie.

I’m 54. The CDC is calling this the worst flu season in nearly 30 years. Over 22 million cases. 280,000 hospitalizations. A mutated “super flu” variant ripping through the country.

I haven’t been sick in over a year.

There’s a reason for that. I’ve been running the same immune protocol since early 2020. And I’m going to tell you exactly what it is.

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How COVID Made Me Take Immunity Seriously

I’d been in the peptide space for a while before COVID hit. But immunity wasn’t really on my radar. I was mostly focused on recovery, body composition, anti-aging. The usual stuff.

Then early 2020 happened.

If you were paying attention back then, you remember the fear. We were watching videos come over from China. People literally dropping dead in the street. Nobody knew what this thing was. Nobody knew how it spread, how deadly it really was, or how to stop it.

For a minute there, it felt like we were looking at the new black plague. Something that could wipe out a huge chunk of the population. That sounds dramatic now, but if you were there, you know that’s exactly how it felt.

And I had a choice. I could sit around and wait for someone to tell me what to do. Or I could do what I always do. Start digging.

So I went deep into the research on what actually builds immunity. Not the surface-level stuff like “take vitamin C and wash your hands.” I’m talking about what really moves the needle at a cellular level. What makes your immune system actually stronger instead of just hoping it holds up.

That’s when I found three peptides that changed everything for me.

Thymosin Alpha-1. LL-37. And Thymulin.

I started running them. I didn’t get sick.

I gave them to my mom. She didn’t get sick either.

My sister actually did catch COVID. She was feeling terrible. I got her on this stack and it knocked it out fast. Way faster than what most people were going through at that time.

That’s when I realized how versatile this protocol really is. You can run it as a preventative to build your immunity up ahead of time. But if something does get through, you switch to a higher dose and it helps your body fight it off way faster. Same peptides, two different approaches depending on the situation.

I’ve been running some version of this stack every flu season, every time I travel, and any time I feel run down. Five years later, it’s still the protocol I trust the most.

Let me break down each peptide and show you exactly how I use them.

Why Your Immune System Gets Weaker as You Age

Before I get into the peptides, you need to understand why immunity becomes a problem as you get older. Because most people don’t realize what’s happening inside their body.

You have an organ called the thymus gland. It sits right behind your breastbone. Its job is to produce and train T-cells. T-cells are basically the soldiers of your immune system. They identify threats and kill them.

Here’s the problem. Your thymus starts shrinking after puberty. By the time you’re in your 40s, it’s a fraction of what it used to be. By your 50s and 60s, it’s mostly been replaced by fat tissue.

Doctors call this “thymic involution.” I call it your immune system slowly going offline.

When your thymus shrinks, you produce fewer T-cells. The ones you do produce aren’t as sharp. Your natural killer cells slow down. Meanwhile, background inflammation goes up. So your immune system gets weaker at fighting real threats while also creating more damage to your own body.

That’s why you get sick more often as you age. It’s not just “getting old.” It’s losing the organ that trains your immune cells.

Now throw in a flu season where a mutated H3N2 variant is sending hundreds of thousands of people to the hospital, and you can see why relying on “hope and hand sanitizer” isn’t a strategy.

The three peptides I’m about to show you address this at the root. Each one targets a different layer of your immune defense.

Thymosin Alpha-1: Wakes Up Your Adaptive Immune System

This is the backbone of the stack. Thymosin Alpha-1 is a 28-amino acid peptide originally found in the thymus gland. Its synthetic version has been approved in over 35 countries for immune-related conditions. It’s one of the most studied peptides on the planet.

Here’s what it does in simple terms.

Your adaptive immune system is the part that learns, remembers, and targets specific threats. Thymosin Alpha-1 is what wakes it up and gets it working properly again.

It takes immature T-cells and pushes them to become fully functional. Basically picks up the slack for your shrinking thymus. More mature T-cells in circulation means your body responds faster and hits harder when something shows up.

It fires up your natural killer cells. These are the first responders. They don’t wait around for instructions. They see something that doesn’t belong and they destroy it. Thymosin Alpha-1 makes them more active and more aggressive.

It helps your dendritic cells work better too. Dendritic cells are like scouts. They find invaders, grab a piece of them, and bring it back to your T-cells so they know what to attack. Better scouts means faster, more accurate targeting.

And here’s the part I really like. Thymosin Alpha-1 doesn’t just crank your immune system up blindly. It balances it. If your immune response is too low, it brings it up. If it’s overreacting (which is what causes cytokine storms), it calms it down. Most immune compounds just push the gas pedal. This one also knows when to tap the brakes.

A 2025 expert consensus published in Infectious Microbes & Diseases produced 10 clinical recommendations for Thymosin Alpha-1 use in infectious diseases and critical care. This is not fringe stuff. This is published science.

This is the peptide I started with during COVID. And it’s the one I’d pick if I could only run one.

How I Run Thymosin Alpha-1

1.5mg daily is what I run. The clinical standard is 1.6mg so you’re right in that range. FDA safety data shows doses up to 16mg for 12 months with no issues, so this is well within safe territory. At 1.5mg/day, a 10mg vial lasts about 6-7 days. For a full 8-week cycle you’ll need about 9 vials.

LL-37: Your Body’s Built-In Pathogen Killer

If Thymosin Alpha-1 is what trains your immune army, LL-37 is the weapon it uses.

LL-37 is a cathelicidin. That’s a type of antimicrobial peptide your body naturally makes. It’s the only one of its kind in humans. Your white blood cells produce it. Your skin cells produce it. It’s one of your body’s original tools for killing pathogens.

Thymosin Alpha-1 handles the adaptive side of immunity. The part that learns and remembers. LL-37 handles the innate side. The part that responds immediately to any threat without needing to figure out what it is first. It just kills it.

How does it kill? It punches holes in things. Seriously. LL-37 physically disrupts the membranes of bacteria, fungi, and enveloped viruses. It forms channels in their cell walls that basically cause them to burst open and die. Research shows this happens within minutes.

And it’s not picky. LL-37 works against gram-positive bacteria, gram-negative bacteria, fungi, parasites, and multiple types of viruses including influenza. During COVID, research showed direct antiviral activity against the virus.

It also breaks up biofilms. Biofilms are like little fortresses that bacteria build around themselves to hide from your immune system. LL-37 tears those structures apart and exposes the bacteria hiding inside.

On top of all that, LL-37 calls in backup. It attracts other immune cells to wherever the threat is. So it’s not just killing pathogens on its own. It’s also telling your neutrophils, monocytes, and T-cells to come help finish the job.

Quick side note. Your body’s natural LL-37 production is tied to vitamin D levels. That’s actually one of the biggest reasons vitamin D supports immunity. It triggers your body to make more LL-37. Supplementing LL-37 directly gives you concentrations way beyond what your body makes on its own. But this is also why vitamin D is part of my supporting supplement stack. More on that below.

How I Run LL-37

125mcg daily is the most commonly cited dose across multiple protocols. Some people go higher (200-400mcg), but 125mcg has a strong track record and is well-tolerated. At 125mcg/day on a 5-on/2-off schedule, one 5mg vial lasts about 40 days. That covers a full 8-week cycle.

Thymulin: Rebuilds the Factory That Makes Your Immune Cells

This is the newest one in my stack and honestly, I think it’s the piece most people are missing.

Remember the thymus gland I talked about earlier? The one that shrinks as you age and takes your T-cell production down with it?

Thymulin is a peptide made exclusively by the thymus. It’s only 9 amino acids. And its job is to support the thymus itself and help it keep producing new T-cells.

Think of it this way. If the thymus is the factory that builds your immune soldiers, Thymulin is the maintenance crew that keeps that factory running. Thymosin Alpha-1 activates the soldiers once they’re built. But Thymulin makes sure they get built in the first place.

A few things that make it stand out:

It needs zinc to work. This is important. Thymulin requires zinc as a cofactor. Without zinc, the peptide is basically inactive. Not enough zinc = Thymulin can’t do its job = fewer T-cells = weaker immunity. Simple as that.

It helps control inflammation. Thymulin shuts down several inflammatory pathways including NF-κB, which is one of the master switches for inflammation in your body. So it supports your immune response while keeping the collateral damage in check.

Connected to sleep. Thymulin levels follow your circadian rhythm. Melatonin actually stimulates Thymulin production. Poor sleep directly suppresses your body’s Thymulin output. Yet another reason why sleep is so tied to immunity.

When you put all three together, here’s what you get:

Thymulin rebuilds the factory (thymus support, new T-cell production).

Thymosin Alpha-1 trains and activates the soldiers (T-cells, NK cells, dendritic cells).

LL-37 gives them weapons (direct pathogen killing, biofilm destruction, immune cell recruitment).

Three different layers. Three different mechanisms. That’s why this stack works.

How I Run Thymulin

I run a 20-day Thymulin cycle 2-4 times per year. Beginning of flu season, mid-winter, and once more in spring. Think of it as seasonal maintenance for your thymus. Don’t skip the zinc. Thymulin without zinc is like putting gas in a car with no engine. It’s not going to do anything.

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The Full Immunity Stack: Prevention Protocol vs. Acute Protocol

This is the part a lot of people ask about. How do you actually structure all three together? And does anything change if you’re already sick?

Yes. It does. Here are both protocols.

Prevention Protocol (Flu Season, Travel, Seasonal Support)

This is what you run when you’re healthy and want to stay that way.

Start with a 20-day Thymulin cycle to prime the thymus. Then maintain Thymosin Alpha-1 and LL-37 for 8 weeks. Repeat the Thymulin cycle every 3-6 months as seasonal maintenance.

This is the protocol that kept me and my mom from getting sick during COVID. You build up your defenses before you ever need them.

Acute Protocol (When You’re Already Sick or Feel Something Coming On)

This is the “all hands on deck” version. This is what I gave my sister when she caught COVID and it knocked it out fast.

When you’re actually fighting something, you run Thymosin Alpha-1 daily and run LL-37 every day with no days off. You’re throwing everything at it. If you’re already in a Thymulin cycle, keep going. But the acute response is mainly driven by Thymosin Alpha-1 and LL-37 working together.

Same peptides, different intensity. Build your immunity up so you don’t get sick. And if you do, hit it harder and recover faster.

The Supplements That Support This Stack (Don’t Skip These)

Peptides are powerful. But they work best when your body has the raw materials it needs to actually use them. I run these supplements year-round, but they become especially important during flu season and whenever I’m running the immunity stack.

This isn’t just a generic “take your vitamins” list. Each one of these plays a specific role in supporting what the peptides are doing.

Zinc (30-50mg daily)

Most important supplement on this list. Not optional. Required.

Zinc is the cofactor that activates Thymulin. Without zinc, Thymulin can’t bind to its receptor. It just floats around doing nothing. Research has confirmed that zinc-deficient people have dramatically lower Thymulin activity.

But zinc does way more than just activate Thymulin. It’s involved in over 300 enzymatic reactions in your body, many tied to immune function. It supports T-cell development, helps white blood cells work properly, and plays a role in wound healing.

Most people are at least mildly zinc-deficient, especially if they sweat a lot, drink alcohol, or eat a lot of processed food. I take 30-50mg daily. Zinc picolinate or zinc bisglycinate for better absorption.

If you’re taking higher doses long-term, add copper (1-2mg daily) to keep your zinc-to-copper ratio balanced.

Vitamin D3 (5,000-10,000 IU daily)

The other non-negotiable. And most people are way more deficient than they think.

Here’s why it matters for this stack: vitamin D directly triggers your body to produce more LL-37. So when you’re supplementing LL-37 as a peptide, taking vitamin D means your body is also making more of it naturally. You’re hitting it from both sides.

Beyond the LL-37 connection, vitamin D supports T-cell function, modulates inflammation, and has been shown over and over to reduce the risk of respiratory infections. One of the most consistent findings during COVID was that people with higher vitamin D levels had significantly better outcomes.

I take 5,000-10,000 IU daily depending on the season. Higher in winter when I’m getting less sun. Take it with a meal that has fat because D3 is fat-soluble. Always pair it with vitamin K2 (100-200mcg) to make sure calcium goes to your bones and not your arteries.

Quercetin (500-1,000mg daily)

Quercetin is a plant flavonoid that does something really specific and useful. It acts as a zinc ionophore. That means it helps shuttle zinc into your cells where it actually needs to be.

You can take all the zinc you want, but if it’s not getting inside your cells, it’s not doing much. Quercetin is the transport system. It opens the door and pushes zinc through.

It also has its own antiviral and anti-inflammatory properties. During COVID, the quercetin-plus-zinc combo was one of the most talked-about protocols in the functional health space. The two are better together than either one alone.

I take 500-1,000mg daily, usually split into two doses with meals.

Magnesium (400-600mg daily)

Magnesium doesn’t get talked about enough when it comes to immunity. But it should.

It’s involved in immune cell activation, antibody production, and the inflammatory response. And like zinc, most people aren’t getting enough of it.

It also supports sleep quality, which directly ties into Thymulin production. Remember, Thymulin follows your circadian rhythm and melatonin stimulates its release. Better sleep = more natural Thymulin output = stronger immunity.

I take 400-600mg daily. Magnesium glycinate or threonate before bed. Glycinate is great for sleep. Threonate crosses the blood-brain barrier and supports cognitive function too.

NAC (600-1,200mg daily)

NAC stands for N-Acetyl Cysteine. It’s a precursor to glutathione, which is your body’s master antioxidant.

Your immune cells burn through glutathione fast when they’re fighting infections. If you’re low, your immune response weakens. NAC keeps those stores topped off.

NAC also has a strong track record for respiratory health. It’s been used clinically for decades to thin mucus and support lung function. During flu season, that matters.

I take 600-1,200mg daily. Higher end when I’m fighting something or around a lot of sick people.

Vitamin C, Liposomal (1,000-2,000mg daily)

Yeah, everyone’s heard about vitamin C. But most people are taking the wrong kind or not enough of it.

Regular vitamin C has poor absorption. Your body can only use so much at a time and the rest gets flushed out. Liposomal vitamin C wraps the C in a lipid layer that dramatically improves absorption. You actually get it into your cells instead of losing it.

Vitamin C supports white blood cell production, helps your body produce antibodies, and protects immune cells from oxidative stress while they’re fighting infections. Nothing fancy. Just essential.

I take 1,000-2,000mg of liposomal C daily. I bump it to 3,000-4,000mg if I’m actively fighting something.

My Full Daily Supplement Stack for Immunity

These supplements cost maybe $60-80/month total. You can get all of them at any health food store or online. No prescription needed. And they make a real difference with or without the peptides.

But when you combine them with the peptide stack, that’s when you’re covering immunity from every angle.

Where I Source These Peptides

I source all three from BioEdge Research Labs. Every batch is third-party tested at 99%+ purity with COAs right on the product page. They focus on peptides and nothing else.

Right now they have these bundled together, so you can save even more if you grab the stack as a package. On top of that, use code MARS15 for an additional 15% off your order.

• Thymosin Alpha-1 (10mg)
• LL-37 (5mg)
• Thymulin

Build Your Defenses Before You Need Them

We’re in the middle of the worst flu season in decades. A mutated H3N2 variant is sending people to the hospital in record numbers. And most people’s strategy is just hoping they don’t catch it.

I stopped hoping back in 2020. I started building instead.

Three peptides to cover all three layers of your immune system. A solid supplement foundation to make sure your body can actually use them. A prevention protocol to keep you from getting sick. And an acute protocol to knock it out fast if something does get through.

This stack kept me healthy through COVID. It kept my mom healthy. It helped my sister bounce back fast when she did get sick. And it’s keeping me healthy right now while everyone around me is dropping.

Build your defenses before you need them. Not after.

Stay protected out there.

Joe Mars
The Peptide Report

This content is for educational and informational purposes only. Peptides discussed are for research use only and are not intended to diagnose, treat, cure, or prevent any disease. Always consult qualified healthcare providers before beginning any peptide protocol.

Frequently Asked Questions About the Immunity Peptide Stack

Can I run all three peptides at the same time?

Yes. They work through completely different mechanisms and don’t compete with each other. Thymulin supports the thymus. Thymosin Alpha-1 activates the cells the thymus produces. LL-37 provides direct pathogen defense. Running them together is the whole point. That’s how you cover all three layers.

How quickly will I notice results?

Immune peptides aren’t like pre-workout. You don’t “feel” them kick in. What you notice is that you stop getting sick when everyone around you is dropping. You recover faster if something does get through. Most people report a noticeable difference within 2-4 weeks of consistent use.

Do I need to cycle these?

Thymulin runs in 20-day cycles, 2-4x per year. LL-37 I run 5-on/2-off for 8 weeks then take a break. Thymosin Alpha-1 I run daily for 8 weeks. It has a very strong safety profile and FDA data supports extended daily use.

Is this stack safe?

Thymosin Alpha-1 has been used clinically in over 35 countries. LL-37 is naturally produced by your own body. Thymulin is made by your own thymus gland. Your body already knows what these compounds are. That said, always approach peptide research responsibly and work with someone who knows what they’re doing.

Do I really need all the supplements too?

Zinc is absolutely required if you’re running Thymulin. Without it, Thymulin doesn’t activate. Period. Vitamin D directly boosts your body’s own LL-37 production. Quercetin helps zinc get into your cells. These aren’t optional add-ons. They’re part of the protocol. The rest (magnesium, NAC, vitamin C) are strongly recommended because they fill in gaps that most people have.

Can I use this if I’m already sick with the flu?

That’s exactly what I gave my sister when she caught COVID. Switch to the acute protocol. Thymosin Alpha-1 daily at 1.5mg and LL-37 at 125mcg daily. The sooner you start, the better.

What if I can only afford one peptide?

Start with Thymosin Alpha-1. It’s the foundation. Most studied, strongest track record, biggest impact on immune support. Add LL-37 next when you can. Then Thymulin. You don’t have to do everything at once.

What if I don’t want to use peptides at all?

Then run the supplement stack by itself. Zinc, vitamin D, quercetin, magnesium, NAC, and liposomal vitamin C will still put you in a much better position than most people. It’s not the same as adding the peptides, but it’s a solid foundation and a huge upgrade from doing nothing.

Peptides can get expensive, but as an FYI - BioEdge is doing 10% off this month (code pep10 at bioedgepeptides.com), one of the few suppliers that consistently delivers what their lab reports claim.

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