If you're looking for an extra pick me up at the office but don't want to endure a day with tightness in your pants, you may not want to order a popular coffee that's being marketed online.

Federal regulators told a Florida paper Monday that Magic Power Coffee contains a drug similar to that in the best-selling Pfizer pill Viagra.

The instant coffee, marketed as a dietary supplement, contains a substance similar to sildenafil, the active ingredient in the prescription erectile dysfunction drug Viagra. Sildenafil can interact with nitrate-type medications commonly taken by patients with hypertension, causing dangerous drops in blood pressure.

"Because this product is an instant coffee labeled as an 'all natural dietary supplement,' consumers may assume its harmless and poses no health risk," said Deborah Autor, director of the FDA Center for Drug Evaluation and Research's compliance office. "In fact, Magic Power Coffee can cause serious harm."

Federal regulators this year have found many similar male enhancement products being marketed as supplements when they in fact contain ingredients reserved for use in prescription drugs, a violation of law.