In the midst of the worst allergy seasons in years, sufferers seeking relief from itchy eyes, scratchy throats, and stuffy noses are reaching in overwhelming numbers for the antihistamine Zyrtec. The allergy drug is one of a number recently approved for use without a prescription, and while this trend toward over-the-counter use may be a boon to allergy suffers in search of a quick fix, some health care experts are questioning the lack of physician oversight, the additional cost to consumers, and the implications for drug manufacturers this trend is having on the industry.

Pharmacists said they barely can keep up with the demand for Zyrtec, approved for over-the-counter use in December. The drug retails at $19.99 for 30 pills.

“Every other day my display for it is empty,” the manager of the Madison Avenue Health Mart Pharmacy, Mark Brandell, said. “It’s the newest thing to come on the market and everyone has the perception that because you needed a prescription, it’s that powerful that it’s going to be great and it works.”

The increased accessibility of Zyrtec comes at a time when pollen is expected to reach record levels. New York’s pollen count, or the number of pollen spores in the air, so far this year is as much as 30,391, an increase of 3,700 compared to last year.

“I hate the term, ‘This will be the worst year ever,’ but this probably will be the worst year ever,” an allergist in Albany who measures pollen counts there, Dr. David Shulan, said.

To meet the needs of the increasing number of Americans suffering from allergies, pharmaceutical companies have rolled out a number of over-the-counter antihistamines in recent years. Last year, a generic form of Allegra appeared on the market, and in 2003 the popular drug Claritin became available without a prescription.

The approval of prescription drugs for over-the-counter use is a relatively new push, and drug regulators have recognized that the risks associated with allergy medications are low compared to the overall benefit, according to a former associate commissioner for the Food and Drug Administration, Peter Pitts.

“The most important issue is, can a consumer safely use this product without the supervision of a physician?” Mr. Pitts, who currently is president of the Center for Medicine in the Public Interest, said.

Allergy medicines are considered relatively safe for use without a prescription, but some patients may simply be treating symptoms of more serious conditions, experts say.

“Many patients with allergic rhinitis have coughing, which can also be a symptom of asthma,” the chief of immunology and allergy at Beth Israel Medical Center, Dr. James Rubin, said. “That asthma is not getting treated.”

Also, consumers must pay more for over-the-counter medications as compared to the co-payments patients typically pay when insurance companies cover the cost. In the case of Zyrtec, for example, consumers shell out nearly $20, while typical co-payments can be as little as $5.

The chief of Mount Sinai Hospital’s allergy clinic, Dr. Beth Corn, recently treated a patient who purchased Zyrtec but found that it did not work for her. “She was reluctant to go on something new because she had just shelled out $30,” Dr. Corn said.

“For the overall health care system, expenditures go down when this becomes an over-the-counter product,” an analyst at Moody’s Investors Service, Michael Levesque, said, citing decreased costs for employers and insurance companies. “Now the burden falls more on consumers.”

Despite higher costs, consumers generally support the shift toward over-the-counter allergy medications.

“It’s a convenience factor,” the managing editor of Consumer Reports Best Buy Drugs, Steven Findlay, said. “You don’t have to go to the doctor if you can get it over the counter and you know which drug works for you.”

The trend toward over-the-counter allergy medicines has also resulted in an increasingly complex relationship between doctors and insurers. “Sometimes it’s a hindrance in that we’d like them to get a certain prescription medication but oftentimes their insurance companies want them to take the over-the-counter version first and have that fail,” the chief of the allergy department at NewYork-Presbyterian Hospital/Weill Cornell Medical Center, Dr. William Reisacher, said. “It’s a little bit of a double-edged sword.”

Drug companies seek approval to sell medications over the counter for marketing purposes. If a drug’s patent is set to expire, selling it over the counter is a way of avoiding generic competition.

In the case of Zyrtec, the patent for the prescription formula was set to expire when the FDA approved it for over-the-counter use in 2007. At the same time, Pfizer, which owned and manufactured the drug, sold its entire consumer products business to Johnson & Johnson. The $16 billion transaction was part of a larger financial strategy for both companies, Mr. Levesque said.

The proceeds from selling off its consumer products business allowed Pfizer to repurchase shares and invest in other business areas, such as biotechnology. Meanwhile, Johnson & Johnson used the acquisition to diversity its products.

“For J&J, it was one more nice brand name to get because a lot of people are familiar with the Zyrtec brand,” Mr. Levesque said.

Company officials declined to provide sales figures for Zyrtec alone, but in the first quarter of 2008, sales for the company’s consumer products business were $842 million, up from $728 million in the fourth quarter of 2007. “They attribute that to Zyrtec,” Mr. Levesque said. He estimated that Zyrtec sales amounted to about $100 million in 2008. “I think that’s impressive for one brand of a consumer product.”