Key Takeaways

  1. Clenbuterol is a powerful stimulant that increases metabolic rate and fat burning and may also reduce muscle loss while dieting.
  2. It’s likely that clenbuterol causes heart damage, insomnia, and potassium deficiency.
  3. In the final analysis, clenbuterol is a high-risk, low-reward drug with safer, natural alternatives.

Hang around in the gym long enough and you’re going to hear about clenbuterol.

Like steroids, “clen” is extremely popular in the world of bodybuilding and is the “go-to” cutting drug for many of the people that step on stage.

Thus, it’s not surprising that it’s also a hot commodity among the general fitness crowd.

If you want to shred fat as quickly as possible without losing muscle, the pitch goes, then you want to hop on the clenbuterol train.

Or do you?

Poke around on the Internet and you’ll find people that think otherwise.

Clenbuterol, they say, isn’t actually all that powerful of a fat burner and is bad for your health to boot, and for your heart in particular, even when used in moderate doses.

Who’s right?

How much can this drug really boost your fat loss? Should you take warnings about side effects seriously, or are they exaggerated? Is there anything else you should know before deciding for or against clen?

Well, you’re going to get answers to all of those questions and more in this article.

By the end, you’re going to know exactly how clenbuterol works, how effective it really is, how likely it is to harm your body, and more.

Let’s get to it.

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What Is Clenbuterol and How Does It Work?

Clenbuterol is a powerful stimulant that increases metabolic rate and fat burning.

It’s sold under different names, like Dilaterol, Spiropent, and Ventipulmin, but most people just refer to it as “clen” or “bute.”

It was originally developed in the 1970’s as a veterinary drug to treat respiratory disorders in horses and other animals. It acts as a bronchodilator, meaning that it relaxes the muscles around airways to make breathing easier.

For a short time, clenbuterol was also marketed as a nasal decongestant and asthma medication for humans. It’s still used as respiratory medication in some countries, but most have switched to safer, more effective alternatives.

Clenbuterol comes in three main forms, too:

  • A drinkable liquid
  • An injectable liquid
  • A pill

None are approved for human use by the FDA, but most bodybuilders choose pills because they’re easy to take, store, and ship (and hide).

Now, how the hell did clen go from something to help horses run better to one of the most popular cutting drugs in all of bodybuilding?

Clenbuterol binds to the same receptors that respond to epinephrine in your body, but clenbuterol produces even greater effects, including fat burning.

Furthermore, clen also binds to muscle cells and stimulates muscle protein synthesis, which is why it also helps you preserve muscle while cutting.

Clenbuterol is a powerful stimulant that increases metabolic rate and fat burning, opens airways, and stimulates muscle protein synthesis.

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Why Do People Take Clenbuterol?

Most people take clenbuterol for one of two reasons:

  1. To improve athletic performance.
  2. To lose fat faster while preserving muscle.

There’s an ongoing debate as to whether it boosts physical performance, but as of now, most studies indicate it probably doesn’t.

There’s no doubt that it speeds up fat loss, though.

Both animal and human research has confirmed that clenbuterol raises metabolic rate and stimulates fat burning, and although it isn’t a steroid, studies show that it stimulates muscle protein synthesis, which will indeed help you retain lean mass while in a caloric deficit.

This is why clenbuterol is all the rage among bodybuilders.

Some even claim that its anabolic effects are powerful enough to enhance muscle building, but this isn’t likely given what we know about it scientifically as well as anecdotally.

Now, just how powerful clenbuterol is as a fat burner is matter of dispute.

Many seasoned users claim it boosts your basal metabolic rate (BMR) by about 10%, and I don’t know of any research that can either corroborate or refute this number. That said, it seems reasonable based on decades of anecdotal evidence.

That brings us to one of the big criticism of the drug: given its health risks (which we’ll talk more about soon), a ~10% increase in BMR really isn’t all that great.

For example, let’s say you’re a muscular guy and your BMR is fairly high—2,200 calories per day, let’s say. Adding clen to your cut would increase this by about 220 calories, which would help you lose no more than a half of a pound of fat per week.

You also aren’t supposed to take clen for more than 4 to 6 weeks at a time because your body builds a tolerance to it, diminishing its effectiveness.

You’ll occasionally hear of people losing 2 or 3 pounds of fat per week with clen, but there’s no scientific and scant anecdotal evidence to back such claims up.

Thus, it’s fair to say that a “cycle” of clen will help you burn maybe an extra 3 or 4 pounds of fat, and that’s only if you have your diet 100% on point. Or you could just stay drug-free and extend your cut by a few weeks to achieve the same effect, and not have to worry about potential side effects…

(And if you’d like specific advice about what diet to follow to lose fat quickly, take the Legion Diet Quiz.)

At best, clenbuterol can help you burn about an extra ½ pound of fat per week.

What Does a Typical Clenbuterol Cycle Look Like?


Most people using clen take it for anywhere from 4 to 12 weeks and often in 4-to-6-week cycles.

In other words, they’ll take it for no more than 4 to 6 weeks before taking a 1-to-2-week hiatus to give their body a break and resensitize to the drug (to maintain maximum effectiveness).

Here’s how the cycle might look:

Week 1: On clen

Week 2: On clen

Week 3: On clen

Week 4: On clen

Week 5: On clen

Week 6: On clen

Week 7: Off clen

Week 8: Off clen

Many bodybuilders also increase the dosage over the course of each cycle.

Standard practice is to start out with a low dosage of 20 to 30 mcg for the first two weeks—about the same amount that was in asthma medication—and then increase to 50 to 120 mcg for the rest of the cycle.

For example, the first 2 weeks of a clen cycle might look like this:

Day 1: 20 mcg

Day 2: 20 mcg

Day 3: 20 mcg

Day 4: 30 mcg

Day 5: 30 mcg

Day 6: 30 mcg

Day 7: 40 mcg

Day 8: 40 mcg

Day 9: 40 mcg

Day 10: 40 mcg

Day 11: 50 mcg

Day 12: 50 mcg

Day 13: 50 mcg

Day 14: 50 mcg

While increasing the dosage does boost fat loss, it also requires careful micromanagement of dosing and carries the risk of overdosing, which can be a frightening and dangerous experience.

Google around and you’ll quickly find horror stories of people who bungled their dosing and wound up on the floor with their hearts beating out of their chests and body temperatures soaring.

Further complicating the matter is you often don’t know how accurate label claims are as most clen on the market is manufactured by fly-by-night chemists running underground labs.

So, when weighed against the negligible benefits, the risk of overdose is another major strike against clen.

Is Clenbuterol Safe?

Most of the research on clenbuterol has been done on animals, so we don’t know enough about how seriously it can affect us humans.

What we do know, though, is it doesn’t look good, which is why clen isn’t approved for human consumption in most countries.

Here’s a list of the potential side effects:

  • Nausea
  • Nervousness
  • Dizziness
  • Drowsiness
  • Dry mouth
  • Facial flushing
  • Headache
  • Heartburn
  • Increased sweating
  • Insomnia
  • Lightheadedness
  • Muscle cramps
  • Vomiting
  • Chest pain

Everyone’s sensitivity to clenbuterol varies, but most will likely experience at least some of these problems when using it.

Here’s what else we know . . .

Clenbuterol Is Probably Bad For Your Heart

The biggest question most people have about clen is if it’s bad for your heart.

And the answer is yes.

First, as clen is a powerful stimulant, it can spike your blood pressure and keep it greatly elevated for extended periods of time.

This, in turn, can increase your risk of left ventricular hypertrophy, or LVH, which is the thickening of the wall of the heart’s left pumping chamber (ventricle). LVH is a major risk factor for heart disease and is also linked with an increased risk of arrhythmias and sudden death.

Unfortunately, as there haven’t been any long-term human studies on clenbuterol use, we don’t know how much clen it takes to get there. We’re going off case studies of people that wound up hospitalized after abusing clen.

Second, there’s evidence that clenbuterol can kill heart cells, which, of course, increases your risk of heart disease.

It’s worth noting that these cases involved people taking very large doses of clenbuterol (several times higher than even most bodybuilders would recommend), but lower doses may physically damage your heart as well. We just don’t know.

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Clenbuterol Interferes with Your Sleep

clenbuterol sleep effects

I mentioned earlier that clenbuterol is a powerful stimulant, and I meant it.

Not only does it spike your metabolic rate, it also stays in your system for far longer than milder drugs like caffeine and ephedrine.

Specifically, research shows that clen can remain in your blood for up to 24 to 36 hours, which is why it’s known to disrupt sleep.

Some people’s bodies clear out stimulants better than others’s, which allows them to take clen first thing in the morning and still sleep fine, but even they tend to experience sleep troubles at some point during a cycle.

Considering the fact that most of us don’t get enough sleep as it is, it goes without saying that taking drugs that further exacerbate this, like clen, is a poor decision for our overall health and wellbeing.

Clenbuterol Depletes the Body of Potassium

Evidence suggests that clenbuterol may cause the body to lose large amounts of potassium and taurine.

Potassium plays an important role in muscle contraction and heart function and taurine may help prevent muscle cramps, so this explains why clenbuterol is linked to heart abnormalities and muscle cramps.

Yes, clenbuterol is legal to purchase, sell, and own in the United States and most other countries.

The reason many people think otherwise is manufacturers aren’t allowed to include it in products that are meant for human consumption, like bodybuilding supplements.

That said, clenbuterol is banned in almost every organized sport because it may enhance athletic performance. For example, both the International Olympic Committee (IOC) and the World Anti-Doping Agency (WADA) have banned the use of clenbuterol, and a surprisingly long list of athletes have been busted for using the drug (strange, considering it likely doesn’t boost performance).

Most developed countries have also banned its use with livestock because it can find its way into the meat, which finds its way into you.

Example: that’s what happened a few years ago to soccer players participating in the Junior World Cup, which was held in Mexico.

Are There Any Safe Clenbuterol Alternatives?

Many supplement companies are cashing in on the popularity of clenbuterol by selling alternatives supposedly comparable or equal to the real thing.

For example, a company called Crazy Bulk sells something called “Clenbutrol,” which they shamelessly refer to as “Clenbuterol” throughout their marketing.

Here’s how the ingredient list looks:

clenbuterol alternative

You can see that it includes . . .

  • Garcinia cambogia, the most overhyped, ineffective rip-off fat loss supplement you can buy.
  • Bitter orange, which contains synephrine and does increase metabolic rate and fat burning, although the dosage is rather low.
  • Caffeine, which boosts metabolic rate and fat burning (at least until you become desensitized to it). Of course, they include it in the form of Guarana extract to make it more exciting and expensive than good ‘ol powdered caffeine, and the dosage is less than a cup of coffee.
  • Vitamin B3, which makes your skin red, warm, and tingly (referred to as a “flush”), and is likely only included to make you feel like the supplement is doing something.

And the price of this underwhelming and definitely-nowhere-near-as-effective-as-clenbuterol supplement? Just $82!

A prime example of what’s wrong with the supplement industry as a whole: way too much bullshit. Bullshit products, bullshit marketing, and bullshit people.

Anyway, the truth is that while there are no “special” forms of clenbuterol that are safer or more effective, there are safe, natural alternatives that’ll help you lose fat faster like . . .

  • Caffeine, which you can find in my pre-workout supplement, Pulse
  • Synephrine, which you can find in my fat burner supplement, Phoenix
  • Yohimbine, which you can find in my pre-workout fat burner supplement, Forge . . .

. . . but you don’t need to pay almost $100 to get any of these ingredients.

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The Bottom Line on Clenbuterol

Clenbuterol will help you lose fat faster, and while it probably won’t help you gain muscle, it’ll help you keep the muscle you have while dropping fat.

It’s legal to buy and easy to get, too, which has helped it become one of the most popular cutting drugs around.

That said, it’s not as effective as many drug pushers claim.

At best, you’re probably looking at a ~10% increase in your basal metabolic rate, which surely helps, but you could also just walk for an hour or so to achieve the same effect.

Furthermore, there’s a very good chance that clen is much worse for you than milder stimulants like caffeine and ephedrine.

We can’t say for sure, but evidence strongly suggests that it increases your risk of heart disease and dysfunction, and especially when doses get high.

It’s also easy to overdose and can even be lethal if taken in too large of amounts or for too long.

So, if you want a simple recommendation, it’s this:

Stay away from clenbuterol.

In my opinion, the risks far outweigh the benefits, and it’s just not necessary to build a muscular, lean, healthy body that you can be proud of.

What’s your take on clenbuterol? Have anything else you’d like to share? Let me know in the comments below!

+ Scientific References