The FDA has issued a warning about an over-the-counter sexual supplement dubbed “Big Penis” — which apparently has men packing more than they bargained for.

“FDA laboratory analysis confirmed that Big Penis contains sildenafil, the active ingredient in Viagra,” said the Food and Drug Administration in a press release this week.

“This undeclared ingredient may interact with nitrates found in some prescription drugs, such as nitroglycerin, and may lower blood pressure to dangerous levels,” the agency explained. “People with diabetes, high blood pressure, high cholesterol, or heart disease often take nitrates.”

FDA confirmed the existence of sildenafil through a random lab test at one of its International Mail Facilities, according to officials.

Including an FDA-approved prescription drug such as Viagra — which is used for erectile dysfunction — with an over-the-counter stimulant is highly illegal and can lead to patients suffering severe side effects that they didn’t sign up for.

“Health care professionals and patients should report adverse events or side effects related to the use of this product to FDA’s MedWatch Safety Information and Adverse Event Reporting Program,” the FDA said. “This notification is to inform the public of products marketed as dietary supplements or conventional foods with hidden drug ingredients and chemicals. These products are typically promoted for sexual enhancement, weight loss, and body building and are often represented as being “all natural.” FDA is unable to test and identify all products marketed as dietary supplements that have potentially harmful hidden ingredients. Consumers should exercise caution before purchasing any product in the above categories.”