LONDON (AP) -- A gimmick timed for Valentine's Day, or a dangerous medical precedent? Britain's biggest pharmacy chain, Boots, will start selling Viagra over the counter at some stores on Feb. 14 — a day also designated in Britain as National Impotence Day.

Doctors are warning of the hazards of making the erectile dysfunction drug freely available to men — especially those with medical conditions such as diabetes or heart problems.

"This sets a very bad precedent and should not be condoned," said Dr. Andrew McCullough, a sexual health expert at New York University Medical Center. "This system is basically prescribing medication without doctors."

Under the scheme, men age 30 to 65 who want the impotence-fighting drug will have a one-hour consultation with a pharmacist, who will take their medical history and check blood pressure, cholesterol and glucose levels.

If no medical red flags are raised, the men can buy four Viagra pills for $97. For a refill, they will have to see a private doctor.

"We're increasing access to Viagra for men who may be too embarrassed to talk about it with their general physician," Boots spokeswoman Clare Stafford said Monday.

But doctors fear the practice could lead to major health problems being overlooked — and set a bad precedent for other countries. In many cases, sexual dysfunction is an indicator of an underlying disease, such as heart failure or diabetes.

Viagra — readily available on the Internet without prescription — was developed by Pfizer Inc. in 1996. It is one of the world's top-selling drugs but is classified as a prescription drug worldwide. Though it is safe and effective, possible rare side effects include vision impairment, heart problems and stroke.

Patrons at a London bar were largely sympathetic to the idea of making the drug available without prescription.

"It's fair play," said Jason Whelan, 30, who was having a beer with friends. He was quick to say he didn't need the drug — yet.

"Come later in life, there's nothing wrong with it," he said.

Doctors believe the system might lead patients to believe that a quick pharmaceutical fix is just as effective as seeing a physician. "There is more to solving sex problems than giving men Viagra," said Dr. David Ralph, a consultant urologist at University College London.

Ralph said the plan would undermine the potential for physicians to make a comprehensive diagnosis, which might even pick up health problems of the men's sexual partners. "If men can just get Viagra at the pharmacy, we are losing the chance to do proper health screening," he said.

In recent years, Boots has introduced similar initiatives with other drugs, such as those for weight loss, hair retention and the morning-after pill.

According to the regulations of the European Medicines Agency, which supervises drug use in Europe, Viagra should be available to men only under medical guidance. "Our stance is clear: Viagra is a prescription drug," said Monika Bernstetter, an agency press officer. "But it's up to member states how they implement prescriptions."

Boots' pilot program at three Manchester-based branches is expected to last six months. The pharmacy will then consider expanding it to other stores.