Back in October, former NBA star Lamar Odom was found unconscious in a brothel in Las Vegas.

The alleged culprit? A multi-day binge that included over-the-counter sexual performance enhancer drugs, known informally as “herbal Viagra.”

Unlike the real Viagra, you don’t need a prescription for these pills—you can pick them up at your local drugstore, gas station, or even online.

Sure, these supplements are often cheaper than what your doctor can order up, and you don’t have to talk to him or her about your sex life to procure them. But you’re putting your health at risk if you take them, says Landon Trost, M.D., a urologist at the Mayo Clinic in Rochester, Minnesota. Here’s why.

Sketchy Ingredients

Unlike prescription drugs or OTC medications, herbal supplements don’t have to be tested or approved ahead of time by the U.S. Food and Drug Administration (FDA).

In fact, the agency released a statement warning consumers against using herbal Viagra products early in October, even before Odom’s event occurred.

Plus, back in 2013, the FDA advised consumers not to purchase Reload, the supplement he reportedly took. (Want to find out what the FDA thinks of a supplement? Stay up to date by checking out FDA.gov/ForConsumers.)

The problem? “We just don’t know what’s in any of these compounds,” says Philip Werthman, M.D., director of the Center for Male Reproductive Medicine and Vasectomy Reversal in Los Angeles.

FDA lab tests have revealed that at least 300 types of herbal Viagra contain ingredients that aren’t on the label.

Some of the undeclared additives often include synthetic versions of tadalafil or sildenafil, the active ingredients in the prescription ED drugs Cialis and Viagra. In fact, one supplement packed 31 times the dose of tadalfil in Cialis, according to a 2013 study in the Journal of Sexual Medicine.

So how do you know if your supplement is potentially dangerous if the ingredients aren’t even on the label?

Follow the FDA’s five rules of thumb: they promise to work quickly, within 30 to 40 minutes; they claim to provide a “natural” or safe alternative to Viagra; they come in single-serving packs; they have foreign languages on the label; or they advertise via spam.

If your pill hits any of those criteria, you want to shelve it.

Serious Side Effects

When doctors write you a prescription for ED drugs like Viagra, they carefully assess your health and current medications to make sure you take the right dose, and that the benefits outweigh the risks.

Pop herbal Viagra on your own, however, and you don’t have the same safeguards.

Prescription oral ED drugs perform their magic by relaxing your blood vessels, so blood can flow into your penis to make you hard. So herbal Viagra supplements that secretly contain some of the active ingredients in these prescription drugs work in the same way, too.

“But they don’t only dilate blood vessels to the penis—they can dilate the blood vessels in other parts of the body,” Dr. Werthman says.

Lax vessels mean less blood flows to critical organs like your brain and heart. Your blood pressure can drop dangerously low, causing you to pass out—or, if it drops so much that your brain gets no oxygen at all, you could even die within four or five minutes, Dr. Werthman says.

These risks run higher for older men or guys who are taking other blood pressure-lowering meds like nitrates, which are often prescribed for chest pain.

That’s why doctors may not prescribe these ED drugs to guys in the high-risk group, and why they set upper limits on dosages when they do write a script. And, they monitor guys closely for side effects and potentially harmful medication interactions along the way.

But if you’re self-medicating on your own with herbal Viagra, you’re probably unaware that you’re creating a dangerous combo.

Plus, there are risks beyond what you’d encounter just taking the prescription. Legit medications are made in FDA-approved facilities, Dr. Trost says.

Though it’s sometimes called “natural,” herbal Viagra is usually produced synthetically too—in unlicensed labs, with no guarantee of purity, he says.

“The problem with drugs in general is a drug may look nearly identical to another one chemically but one small change of a nitrogen group added here or an oxygen group added here can have a big difference in the body,” Dr. Trost says.

As for the tweaked compounds in faux Viagra? “We don’t have good data on the safety of any of those,” he says.

Plus, FDA and other tests identified random, undeclared ingredients, such as caffeine and other stimulants in these supplements. These can cause harmful side effects like irregular heartbeats, especially if you have a congenital heart defect, Dr. Trost says.

Mixing natural ED pills with alcohol or other recreational drugs—as Odom reportedly did—is an even worse idea.

Depressants and stimulants can affect your heart and blood vessel function, adding to the risk of low blood pressure and other heart problems.

Combine that with a slowed-down respiratory system, which you’ll often get when you take too many opioids or cocaine, and you run the risk of respiratory failure, Dr. Werthman says.

The bottom line—you just don’t know what’s in these pills, and what they’ll do to your body.

“It’s like you put your hand in a grab bag and you end up with a random drug,” Dr. Trost says. “You take it and you wait to see what happens.”

What You Should Do if You Have Erectile Dysfunction 

First of all, avoid these prescription-free supplements that promise you “natural sexual enhancement.”

Next, focus on your overall health, taking steps such as losing weight and cutting back on booze, Dr. Trost says.
If you tried making lifestyle modifications and still can’t get an erection, see your doctor. Even in younger guys, ED can signal larger health problems, including diabetes or heart disease, Dr. Trost says.

But it’s more likely that temporary stress or lacklustre sex has left you with performance anxiety. A short course of treatment with prescription ED drugs or psychotherapy can get you back in action, says Dr. Trost.

“All we have to do is break patients out of that cycle to where they get reliable erections for a period of time,” he says. “Then they often can go back to not needing any therapy.”