Syntheroid Testosterone Booster Review: Does It Work?

When I first heard the name Syntheroid I thought it was a supplement for the thyroid because its name sounds a LOT like the drug synthroid that people take for hypothyroidism.  But Syntheroid is billed as a natural testosterone booster whose motto is “power, mass, sexual performance.”  The makers of Syntheroid  claim that it can improve speed, agility and reaction time, as well as muscle size and strength.  This is in addition to the claim that Syntheroid can maintain libido during hard core dieting.  These are all pretty bold statements so I’m not surprised if people wonder if Syntheroid really works or not?  Let’s now review Syntheriod and what can be discovered.


Who makes Syntheroid?

If you check the product website – -you can’t find out who makes this product.  Its only after some digging that I discover that syntheroid is made by a company called XPI (  Why the XPI website is not listed on the website does not make sense.

The address of XPI labs is 965 N 1430 W  Orem, UT 84097.  The link provided is to show what the area looks like.  I see a lot of warehouses.  I did not see any building called “XPI laboratories” but since most of the buildings appeared dull looking – built for function, rather than looks -  I’m sure its in there somewhere.  XPI labs does not seem to have a BBB listing when I checked on 12/7/11.

On the website there is a video of a 31 year old man named Josh Dahl (“The Josh Dahl Story”) where he says that Syntheroid makes him feel like he’s 21 years old again.  They listed his name like we should know who Josh Dahl was – which I didn’t – so I did some goggling on who Josh Dahl, was but could not find anything.  Maybe Syntheroid did do what Josh said but in general I take all testimonials from people I do not know with a big grain of salt.


Syntheroid ingredients

Kudos to the Syntheroid website because they do tell us what’s in this product. If you take 3 capsules of Syntheroid -the recommended dose – you get the following:

Tribulus Terrestris650 mg
Testofen300 mg
Aminogen250 mg
Coleus forskohlii125 mg
Milk Thistle120 mg
Alpha lipoic acid100 mg
Eurycoma Longifolia100 mg
Horny goat weed100 mg
Bioperine15 mg



Remember, even though the name syntheroid sounds like a drug, syntheroid is not a hormone or a pro hormone. It’s a dietary supplement. They even say this on the Syntheroid website.


Looking over this list of ingredients, Syntheroid has some things found in many other products I’ve reviewed in the past.

For example, Syntheroid has Tribulus. I know people have said that tribulus works for them but I have been skeptical about the claims of this herb since the 1990s when it first started getting popular. For more on this, do read my Tribulus review after your done reading.

Despite the hype about tribulus and testosterone, I can’t find any proof that it works. For example, in a study published in 2001, tribulus didn’t work. In another study from 2007 tribulus didn’t work.

If anybody knows of a“tribulus raises testosterone study”, please let me know and I will happily update my reviews on this herb.

Now, no study is perfect, so if you really want to know if tribulus raises testosterone, get your doctor to check your testosterone before starting tribulus (or Syntheroid) and after a month of using it.  This is the only way you can know for sure if it worked or not.

As for Testofen, it’s a cool sounding name and was likely invented to give the impression that it raises testosterone – but it doesn’t. Testofen is just an made-up name for the herb Fenugreek. For more on fenugreek- testosterone research also see my review of Ageless Male.

Fenugreek might raise insulin levels. Since insulin helps us use amino acids, that means it has a mild anabolic effect. I’m guessing this is why it’s in a testosterone booster supplement. Here is Fenugreek on Amazon.

Ironically, this effect on insulin is why fenugreek is also found in diabetes supplements.  For example, the diabetes supplement Glucotor V2 also has fenugreek. In fact, this diabetes supplement has the same amount of fenugreek – 300 mg – as Syntheroid does.


Aminogen. The Syntheroid website says that Aminogen is a ” proprietary proteolytic synthetic enzyme” that  “was created to improve protein digestion and absorption.”  That means at that Aminogen is not an amino acid supplement but rather just a fancy name for a protein digesting enzyme supplement.

Unless you have a problem absorbing protein you don’t need enzyme supplements.  They say that Aminogen “works to produce a higher bioavailability within your body particularly to your muscles.”  So, where is the proof of this?  As far as I can tell neither Aminogen – or Syntheoid – has any peer reviewed clinical proof that it does anything.  Since they can’t prove to me that this statement is true, I discount it.


Just a heads-up, animal protein – has a very high absorbability, so unless your doctor has told you that you have a problem with digestion, you don’t need any supplemental digestive enzymes.  What’s a good way to remember animal protein? It’s any food that had a mother. That’s how I remember it!


Coleus forskohlii.  This herb is said to be a metabolism booster and weight loss supplement. The idea here is that coleus forskohlii (forskolin) stimulates fat burning enzymes that help us lose weight. One small study of older, overweight men also noted that coleus forskohlii increased testosterone levels.

This is the logic why Coleus forskohlii is found in many weight loss products such as Lean and Fab and Apidexin to name a few.

Here is coleus forskohlii on Amazon.

The problem with coleus forskohlii research is that they often have problems and so for the moment, I will keep an open mind about forskolin until better research is done. For more on this research, read my Coleus forskohlii review.


Milk Thistle.  Since steroid abuse is thought to damage the liver, and since Syntheriod is reputed to be a testosterone booster, I’m guessing this is why they added the liver protecting supplement -milk thistle – to Syntheriod.

That is the most obvious answer I can guess, because there seems to be no clinical proof that milk thistle raises testosterone or improves libido. There is interest in milk thistle for diabetes because it has been shown to reduce blood sugar levels.

Might stabilizing blood sugar levels help people have better workouts? In theory, maybe. This might be another reason for putting milk thistle in Syntheroid.

Mostly this herb is an antioxidant and one of its active ingredients is a compound called Silymarin.  Syntheroid has 120 mg of milk thistle but I can’t tell from the product website how much Silymarin this translates into.


Alpha lipoic acid.  Like milk thistle, alpha lipoic acid has also been researched for its blood sugar lowering effects.   I’ve seen this stuff used in many exercise and weight loss supplements despite any good proof it helps weight loss or exercise.

For example, alpha lipoic acid is also found in the bodybuilding supplement Stemulite and Jillian Michaels Fat Burner as well as the Plexus Slim weight loss supplement.

Like several other ingredients in Syntheroid, eurycoma longifolia is found in variety of other products. For example, this herb is one of the main ingredients in TriVerex – a male enhancement product you may have see on late night TV.

It’s probably eurycoma longfolia – as well as horny goat weed – that are at the heart of the claims that Syntheroid improves sex. I don’t want to reinvent the wheel on these ingredients, so please read my words on TriVerex” for more info on the research behind both eurycoma longfolia and horny goat weed.

The same thing goes for Bioperine. For more on this ingredient see my Lean and Fab review.


Syntheroid side effects

I think if you are healthy you might not notice any differences with Syntheroid.  If you are not “healthy” or take any medications, see your doctor first.  Syntheroid is probably very safe in healthy people but as far as I can tell this assumption has never been tested. Here is Synteroid on Amazon for those who want to check out the comments from others who have used it.

One older study noted that alpha lipoic acid might lower thyroid hormone levels.  If this holds true, it might also reduce vitamin D levels as well as metabolic rate.  I’m not sure if this “side effect” is true or not  but it’s worth mentioning just in case you have hypothyroidism. Alpha lipoic acid might also add to the effects of insulin and other diabetes drugs.

Fenugreek might cause hypoglycemia (low blood sugar) and interact with insulin or other blood sugar lowering medications.  It might have an even greater blood sugar lowering effect when combined with alpha lipoic acid.

Milk thistle might interact with many medications like coumadin (a blood thinner). The herb might also have an estrogen effect that might be bad for women with a history of breast cancer. This effect is probably a long shot, but speak to your doctor if you are not “healthy” just to be safe.


How much does Syntheroid cost?

They say 1 bottle currently costs $59.95 on the Syntheroid website. I think that is a lot of money for a product that has zero clinical proof that it works.

Here is Synteroid on Amazon to compare prices.


Does Syntheroid work?

Well, on the XPI labs website they say that Syntheroid “was scientifically formulated to boost testosterone levels, improve protein synthesis, absorb nutrients, and burn fat faster than any other legal supplement on the market.”  Scientifically formulated?  How did they scientifically formulate this product but did not conduct any scientific tests to prove Syntheroid actually does what they say?

In my book, you can’t invoke the name of the mighty god science (lowercase g) without following through by doing actual scientific testing – in humans.  Failure to do so is just bad science.  They also say that with Syntheroid, you can boost testosterone by up to 400%.  Again, where is the proof?  Actually if you look closely at the XPI labs website, they didn’t really say Syntheriod would boost testosterone by 400%.  Rather, they just plastered the saying “Boost Testosterone by up to 400%” on the web page to make you think that is what it would do.  There is no supporting evidence for this claim.

I think Syntheroid is just another overpriced bodybuilding supplement that is long on marketing and short on science but I’m open to hearing what the users of Syntheroid are experiencing. If you are interested here is Synteroid on Amazon.

What do you think?


  1. Chad says

    I hate to sound harsh, but you could have skipped the “fluff” and gone strait to the ingredients.

    I don’t care if there isn’t a link to XPI supplements home page, they have a giant XPI logo on the bottle and the website.They obviously aren’t hiding anything,

    I also don’t care if their building doesn’t have an XPI logo on it. I checked and USPLabs, Cellucor, MusclePharm, BSM, and other big companies. They don’t even give you their address. Who cares?

    i love reading your reviews, but lets stick to the stuff that matters.

    • Joe says

      Chad, thanks for the feedback. I cover the stuff on the companies because I feel it adds to the totality of the review. Companies that have “lab” in the name gives the impression to me that they physically exist as a “lab” or do laboratory research and so pointing out that that this might not be so, I feel, adds to the review. I do try to make the sections easy to skim so people can get to the areas they are interested in quickly, so I hope this makes up for things.

    • Joe says

      Greg, for me, none stand out because none of those Ive seen have given me any proof they would really work in people. Best I can say is get T measured before you try anything (free T and bound T) try a product for a month and retest T. Thats the only way to know for sure. Its good for all men to get their testosterone measured anyway at least to see if they are low or not and to get some baseline #s that doctors in the future might be able use to tailor treatments better.

  2. Roger Smith says

    Joe, is right, I’ve been on this product for the past 6 weeks, I have followed all the instructions, and done all the exercise, and saw no results, I feel the same way after taking this product, the only good thing about it is that they got a 30 days money back, and I returned my leftover. Thanks, Roger

    • Joe says

      Thanks Roger and for what its worth, sorry it didn’t help you but I am glad you were able to get your money back from the company.

    • Joe says

      Dude, there was no D Aspartic Acid in Syntheroid when I reviewed it. Thanks for the heads up I’ll look at updating what I wrote.

  3. Powbeech says

    Reply to my own reply:

    it is possible that they improved the formula by adding this and other ingredients since your review.

    • Joe says

      Powebeech, supplement companies do update their formulas from time to time. Since I dont know when this happens, I do appreciate it when people like you tell me about this. D aspartic acid has been something Ive wanted to look at anyway so Ill update my review with this ingredient in the near future.

  4. Jimmy says

    Joe, what is your opinion on Gaspari supplements? I remember when I was younger Rich Gaspari was quite a beast in the gym world and I am wondering if his supplements are considered worth it.

    • Joe says

      Jimmy, Ive never heard anything bad about Gaspari supplements but my question is are they any better than other supplements that have the same ingredients?

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