We have a new, firm warning from the American Association of Nurse Anesthetists to the millions of men taking erectile dysfunction ED drugs, who may be headed into surgery.

When combined with anesthesia, medications such as Viagra (sildenafil), Levitra (vardenafil), and Cialis (tadalafil) can cause a dangerously severe drop in blood pressure.

That's because ED meds contain — and promote the body's own ability to produce — nitric oxide, which opens blood vessels and relaxes muscles, making it much easier for erections to occur.

Adding anesthetics and other medications used during surgery to the blood-vessel dilating actions of an ED med can increase those effects.

Because the average American male can expect to undergo more than nine surgical procedures during his lifetime, and a growing number of ED pills are dispensed to men in the U.S. (annually it's around 1.2 million Viagra and almost 3.6 million Cialis), this is a warning lots of guys need to take seriously.

We also predict that when generic Viagra is available this December, there will be a big increase in the size of the market — and with that, an increased risk for the one-two punch of ED drugs and anesthesia.

Our advice if you're taking an ED medication and headed for surgery:

• Stop taking ED drugs 48 hours before the procedure; that will allow the drug to clear your system.

• Before surgery, alert your anesthesiologist to all medications and supplements you're taking, including ED meds.

Your emergency contact also should know to tell medical staff about any ED drug use.