NEW YORK (CNN/Money) – With earnings season just around the corner, a somewhat disturbing trend has emerged. Companies that had been considered "safe havens" have finally been cracked.

Recent earnings warnings from tech and telecom companies and big investment banks aren't exactly surprising. But now that companies in the drugstore, supermarket, fast food and tobacco industries -- groups that market experts have typically dubbed "recession-proof" -- have started to report disappointing results, it just goes to show that there really is no such thing as a truly safe stock.

"One of the fallacies of investing is thinking that there are companies immune to weak economies," said Subodh Kumar, chief investment strategist for CIBC World Markets.

Take a look at drugstore chain Walgreen. Although the company did report earnings growth of 14 percent on Monday, it missed estimates by a penny and the stock plunged more than 9 percent.

Granted, Walgreen's fundamentals have been far better than a company like IBM or Citigroup, for example (it was still sitting on a year-to-date gain as of Friday). But the company couldn't completely escape the economic downturn.

"Walgreen is bound to slip up every now and then," said Ted Parrish, co-manager of the Henssler Equity fund and an owner of Walgreen stock. "Consumers are not going to stop buying prescription drugs, but they can stop buying the Big Mouth Billy Bass at the front of the store."

To that end, shares of supermarket chain Kroger were still in the black for the year as recently as mid-June and had outperformed the S&P 500 up until late August. But the company issued an earnings warning on Sept. 17, citing "price-sensitive customers" as a primary reason for the lowered forecast.

McDonald's has been reeling of late, so investors might not recall that the stock actually finished the first half of the year with a gain. Earnings in the second quarter increased 15 percent from last year. It wasn't until the company issued an earnings warning on Sept. 17 and announced that it was scaling back the opening of new restaurants that the stock took a supersized plunge.

Then there's Philip Morris, the ultimate safe haven. Cigarettes are addictive, after all. The stock had been chugging along, bucking the market's downward trend all year. It was still clinging to a year-to-date gain on Sept. 18. But since then, the stock has plunged 18 percent and is now down 14 percent for the year.

Part of the decline can be attributed to re-ignited fears about class-action lawsuits by smokers. But the biggest blow came Thursday when Philip Morris shocked the market with an earnings warning. Among the factors that the company blamed for the lowered outlook were "weak economic conditions ... and heightened consumer frugality."

While it's clear that the economic woes have finally hit so-called safe havens, the more important question is how long will these companies struggle. Is this the beginning of a prolonged decline or just a short-term blip?

Kumar thinks there's a good chance the food and grocery retailers and the fast-food chains will disappoint investors in the coming months. That's because many of them have chosen to spend heavily on marketing in order to spur consumers to spend, as opposed to moving to cut costs. While this might increase revenue, it could come at the expense of profit margins, he said.

But Parrish said that for select consumer oriented companies, poor fundamentals are a short-term problem. Barring a major downturn in consumer spending, companies like Walgreen, PepsiCo and Anheuser-Busch are safer investments than companies in the financial and technology sectors, he said. Parrish owns PepsiCo and Anheuser-Busch in his fund.

That said, nothing's 100 percent safe. "An economic downturn affects all companies, some less than others," Parrish said. He's avoiding supermarket chains because competition is too cutthroat. He also thinks McDonald's woes will continue since it is a mature business.

And what about tobacco? Dan Ahrens, co-manager of the Vice Fund, thinks the market's reaction to Philip Morris's warning was overdone. He said he bought shares of Philip Morris following the warning and also increased his stake in British firm Imperial Tobacco. Ahrens said he does not expect tobacco stocks to falter for long since they have weathered downturns before.

"This industry has been through thick and thin and litigation concerns over the past 30 years," Ahrens observed. "I don't care what the stocks are doing on a day-to-day basis."