How Much Icariin Equals Viagra?

By The Rex MD Editorial Team

December 1, 2020

If you've done any research on erectile dysfunction, you'll probably recognize the names Horny Goat Weed and Icariin. These herbal, natural solutions are sold over-the-counter as naturally derived remedies for erectile dysfunction (ED). Icariin is the compound in Horny Goat Weed that's credited with its alleged erection-causing capabilities.

Alleged is the key word here. Unlike Viagra and Cialis pills, neither Icariin or Horny Goat Weed are approved by the U.S. FDA for the treatment of erectile dysfunction. FDA approval is the most rigorous process a possible medication go through, having proved to this U.S. regulatory agency that the medication is not only safe in humans, but also effective. The FDA has helped keep many fake, snake oil products off the market.

Still, millions of guys every year try these natural ED remedies.

Is it worth it? Does Icariin really work? Does Horny Goat Weed work like Viagra?

Here's what the research on Icariin says so far.

What Is Icariin?

Icariin is a chemical compound that comes from several species of plants in the genus epimedium. They're native to China and Asia and are known as Horny Goat Weed, Fairy Wings (epimedium grandiflorum), Barrenwort (epimedium brevicornum), and others.

Horny Goat Weed herbal extract is the most well-known of the epimedium erection champs, and it's been used for generations in traditional Chinese medicine for its aphrodisiac qualities.

Through its use as an ancient Chinese herbal remedy, there is some evidence to support Icariin's potential for ED. You see, this compound is a mild inhibitor of the Phosphodiesterase-5 enzyme (PDE5 inhibitor). PDE5 inhibition is the exact same way that Viagra (sildenafil), Cialis (tadalafil), Levitra (vardenafil), and other FDA-approved ED medications work.

Inhibiting PDE5 is a recognized mechanism to alleviate ED quickly and improve erectile function.

Icariin inhibits PDE5, so does it work for ED? Is Horny Goat Weed a miracle herb?

First, How Does PDE5 Inhibition Work?

Viagra (active ingredient sildenafil citrate) was the first oral medication approved by the FDA for erectile dysfunction in men. While more PDE5 inhibitors have come along since then, it's still the most popular quick-acting and potent erectile dysfunction drug.

Inhibiting PDE5 in the male body can improve blood flow and arterial pressure in the smooth muscle of the penis, and help to induce an erection. Here's how it works.

Normally, a few processes in the body contribute to an erection. When a man is sexually aroused, either through psychological or reflexive stimuli, nerves in the penis release nitric oxide. This stimulates muscle cells in the penis to make more of a molecule called cyclic GMP (cGMP).

cGMP increases and accumulates in the muscle cells, which activates a number of other effects (lowering cytosolic Ca2+, desensitizing to cytosolic Ca2+). Ultimately, cGMP leads to relaxation of the smooth muscle vasculature in the penis, penile arteries, and the corpora cavernosa, the big spongy penile tissue on each side of the penis shaft that fill with blood during an erection.

More cGMP means more blood flow as the blood vessels relax and widen.

Meanwhile, PDE-5 (phosphodiesterase-5) is an enzyme in the body that breaks down cGMP. (Think back to high school chemistry and you'll recall that enzymes are proteins that catalyze a reaction.) As it eliminates cGMP, the erection processes slow down and/or stops completely. You can think of PDE-5 as a braking system on the erection. It's a totally normal biological process.

Sildenafil (Viagra) and other PDE5 inhibitors stop this enzyme from doing its normal job of breaking down cGMP. As they do this, they're releasing the usual brakes on the erection/arousal system.

One thing that's important to know about erections and proper sexual function is that sildenafil doesn't CAUSE an erection. That's why men still need sexual stimulus to get things started. Sildenafil and other PDE5 inhibitors just keep things moving in the right direction and release the brakes on the system for better sexual performance. Don't expect to get a raging hard-on just by popping this little blue pill; you'll still need a little intimacy to warm things up.

How Much Icariin Equals Viagra (sildenafil)?

Icariin is a PDE5 inhibitor too. But here's the thing: it's incredibly weak when it comes to improving blood flow through PDE5 inhibition in the body.

One of the more robust attempts to work out Icariin's potential effectiveness in ED came from from Italian researchers in 2008. This team looked at the PDE5 inhibiting qualities of a handful of natural, alleged aphrodisiac plants, including Horny Goat Weed. They found that Icariin was the most potent of these...but it still fell well short of Viagra.

Scientists measure the ability of a compound to "work" on its intended target by something called the IC50, which quantifies how much of a compound it takes to inhibit the target by 50%. In this case, the researchers were looking at how much Icariin it took to inhibit PDE5 function by 50% (the IC50).

These researchers found that Icariin has an IC50 for PDE5 of 5.9 micromolars, while sildenafil has an IC50 of 75 nanomolars. Converting both to nanomolars (nM), that's 5900 nM for Icariin to have the same effectiveness as 75 nM sildenafil! Sildenafil is about 78 times more potent than Icariin and Horny Goat Weed based on these observations.

Hands down, when it's sildenafil vs Icariin...Viagra is better than Icariin.

A Natural Viagra Alternative?

Part of the reason so many men - and researchers - have been interested in proving that Icariin works is that it could be a compelling all-natural alternative to Viagra. That's partly because Viagra has some side effects in a small portion of men who use it, and the hope is that a natural alternative with different targeting could improve on Viagra. Sildenafil works well because it's so selective to PDE5, meaning it usually has few other side effects in the body. This "selectivity" is part of what makes it a great drug, but could something even more selective work even better than Viagra?

So, in looking for a more natural aphrodisiac, the researchers took things a step further by making a small chemical modification to the Icariin molecule. Of the five Icariin derivatives that emerged from these lab studies, one of them was a more potent and more selective PDE5 inhibitor than the original Icariin.

This "compound 5", as they called it, had a PDE5 inhibitory potential of 80 TIMES that of icariin in their study. They concluded: "its selectivity and lack of cytotoxicity make 5 a candidate worthy of further study."

That's potent stuff compared to sildenafil, so what happened? Unfortunately ss far as we know , further research never happened on this selective new phosphodiesterase inhibitor.

Horny Goat Weed Dosage

So, if Icariin sorta-kinda works, does Horny Goat Weed work?

Horny Goat Weed is available over-the-counter as a supplement to help with ED. It contains Icariin, but of course Horny Goat Weed is a much more unique name, so it's the name you often see. The name allegedly comes from an ancient goat herder whose herd ate the plant and immediately became more promiscuous.

Popular Horny Goat Weed and Icariin supplements are available online and in drug stores at suggested doses of 900 mg to 1500 mg daily. They often come in 500-750 mg capsules.

Not only is it potentially a poor molecule for improving ED, but Icariin supplements are often not very pure or "bioavailable." Bioavailability refers to the amount of a chemical that goes into your bloodstream after ingesting it, in the case of oral supplements. If only a portion of the intended icariin is reaching the bloodstream, it requires an even larger upfront dose to achieve substantial PDE5 inhibition in the blood. For many over-the-counter supplements, we don't know the true bioavailability.

As illustrated above, it would require a HUGE amount of icariin to rival the effectiveness of sildenafil (Viagra), and unfortunately Horny Goat Weed supplements and capsules are probably inadequate unless you're going to eat it by the plateful.

Icariin Vs Viagra: The Verdict

No OTC supplement has been able to rival the potency of the little blue pill Viagra (sildenafil) or other PDE5 inhibitors approved by the FDA, and the verdict on the natural alternative Horny Goat Weed is hazy at best. While men have reported anecdotal success for generations using this and similar plant-based remedies, research comparing Icariin to sildenafil directly in humans has never been done. But the in vitro data seem conclusive enough (and are probably why no one's bothered to test the two head-to-head): Icariin just doesn't have the same potency as Viagra.

The good news is: you can get prescription ED treatments including on-demand sildenafil (Viagra), daily tadalafil (Cialis), and more without ever leaving home. Try RexMD's telehealth platform to save money, time... and maybe even your marriage.

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Disclaimer : This article is for information only and should not be considered medical advice. Always speak with your doctor about your health and the benefits or risks of any treatment or intervention. This information should not be relied on as a substitute for professional medical advice.