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One of the casualties of America's war on drugs are under-informed prescription drug users.

When one prescription drug interacts dangerously with another prescription drug, manufacturers and pharmacists are duty-bound to inform patients. But when the risky interaction is with non-prescription drugs (i.e., street drugs), state-licensed pushers keep mum, not wanting to acknowledge illicit drugs' existence nor to create any obligation to investigate recreational or therapeutic drug use from which no NASDAQ-listed company profits.

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Last year it was AIDS treatment activists who had to warn users of Ecstasy that the protease inhibitor Ritonavir could significantly and dangerously potentiate Ecstasy's effect, and that at least one death seems to have been the result of mixing the two.

Now comes Viagra, the super-popular erection-enhancing pill. The package insert from manufacturer Pfizer warns that Viagra should not be taken by those also using nitrate-type drugs (like nitroglycerine, used to treat angina-- a heart condition), but does not explicitly mention that "poppers" are of this class. Using poppers with Viagra (a not-unlikely combo) can result in serious hypotension (low blood pressure), wherein a formerly blissful haze can spiral downward to unconsciousness or death.

And the same pharmacological mechanism (inhibition of the enzyme p450 3A4, which breaks down drugs in the liver) that makes Ritonavir magnify Ecstasy's blood levels also makes it boost the effects of Viagra. Pfizer does officially note this interaction, but doesn't expect the results to be dangerous, though they suggest patients using Ritonavir should start with the 25 mg dose of Viagra rather than the usual 50 mg. And since the drug is cleared from the blood more slowly (as Ritonavir ties up ones p450 3A4), the erection-enabling effects are likely to last well-beyond the few hours enjoyed by those not on Ritonavir. Perhaps it is with compassionate irony that diseased pariahs are thus granted at least one side-effect that they may celebrate.

AIDS Treatment News reports that Viagra is not expected to affect the blood levels of protease inhibitors, nor of other drugs commonly used in HIV treatment.