When autopsy results came back on a 16-year-old Orinda boy who died at a house party where teenagers had been drinking, two findings took investigators by surprise.

Joseph Loudon's blood-alcohol level was only 0.03 percent, which was low considering reports that hard liquor seemed to be in ample supply at the May 23 party, held at the home of a friend who lived on the same street as Joseph's mother. A 0.08 percent level constitutes drunken driving.

And his body showed high levels of papaverine, a prescription medication commonly used to treat erectile dysfunction.

That led to the natural question: Why was a 16-year-old boy using a drug typically prescribed for impotent middle-aged men?

It's not known whether Joseph was using the drug recreationally, whether someone slipped it to him in a drink, or whether there is another explanation. Combined, the erectile drug and the alcohol caused Joseph to throw up, and he choked on his vomit, the Contra Costa County coroner found.

Drug not in house, dad says
"I have no idea how Joe might have obtained the drug or why it was in his system," said Joseph's father, Bill Loudon. "It is not a drug that was in either my house or that of his mother."

In a letter Wednesday to Contra Costa District Attorney Robert Kochly, Joseph's mother, Marianne Payne, wrote, "I am now more certain than ever that the circumstances of Joe's death are quite serious - and that the truth must be known."

Papaverine is available only with a doctor's prescription, and Joseph was not taking any prescribed drugs when he died, said Orinda Police Chief Bill French.

The drug is a vasodilator, meaning it relaxes the muscles in blood vessels and makes them bigger. Brand names include Cerespan, Genabid, Pavabid and Pavacot.

Papaverine is particularly helpful during certain vascular surgeries, said Dr. Tom Lue, a professor and vice chairman of urology at UCSF. "It makes blood vessels bigger so we can do operations easier," Lue said.

Its effects on blood vessels are precisely why it works wonders in treating impotence, experts say. Papaverine can be injected directly into the penis to stimulate blood flow. The drug can also be taken orally in tablets or extended-release capsules.

"It is the first drug ever shown to create a pharmacological erection," said Dr. Mark Litwin, a professor of health services and urology at UCLA.

'First we heard of this drug'
Authorities said they had not heard of any accounts of teenagers using papaverine - or any erectile-dysfunction drug, for that matter - recreationally.

"That was the first we heard of this drug," French said, adding that if there was a recreational use for papaverine, "we're unaware of it."

Drug-addiction counselors at Walden House in San Francisco also have not heard of any cases involving the abuse of erectile-dysfunction drugs, said spokeswoman Joni Rocks. "We really hadn't heard of anything like that," she said.

But San Mateo County Coroner Robert Foucrault said his office had investigated the case of a man in his 20s who ingested Viagra and died as a result of autoerotic asphyxiation, in which people accidentally suffocate while intentionally cutting off their airway to enhance sexual pleasure.

Litwin said, "Certainly you wouldn't think a 16-year-old would need to take any medication for erectile dysfunction. The recreational use of erectile-dysfunction drugs are typically seen not in teenagers, but typically in older young adults who are using other drugs that might compromise erection. But a 16-year-old sounds extraordinarily rare."

Sports-related asthma
Payne told authorities that her son's only medical condition was sports-related asthma, in which strenuous exercise triggers asthma attacks, the coroner's report said. Joseph was on the track team at Miramonte High School in Orinda and played on a regional rugby team.

Orinda police have arrested three people connected to the party for allegedly furnishing alcohol or fake ID cards to minors. They are still investigating Joseph's death, including why he had papaverine in his system.

Bill Loudon said, "If he also chose to take a prescription drug, and it is hard to believe that he did that intentionally, then that too was a mistake. His mistakes that night, large or small, cost him his life and cost me my son."