In 2008, the U.S. Food and Drug Administration announced that conventional cold and cough remedies could be deadly for children under age 4 and may cause serious health problems for kids as old as 11.

Two years later, the Cochrane Vaccines Field (CVF), a group that studies the safety and effectiveness of vaccines, released its review of flu vaccines. The findings shocked millions of people who dutifully grit their teeth and bare their arms for yearly flu shots. The CVF analyzed 50 studies conducted between 1966 and 2010 and concluded that flu vaccines have only a “modest effect in reducing influenza symptoms and working days lost.” In addition, researchers discovered that the chance of getting the flu if you’re unvaccinated is only 2 to 4 percent, versus 1 percent if you’ve been vaccinated.

It’s no surprise that this news has spurred a search for alternatives. As a result, a growing number of people are discovering that, unlike conventional products, immune-enhancing herbs that fight colds and flu are virtually free of side effects. What’s more, research shows they can be as effective as or sometimes even more effective than their conventional counterparts. Here’s a look at the top three.

Echinacea

Perennially one of the best-selling herbs, echinacea took a hit after a well-publicized 2005 clinical trial revealed that it not only didn’t prevent upper respiratory tract infections, it didn’t treat them either. Herbalists and alternative medical practitioners blasted the study, pointing out that the researchers used echinacea dosages of about a third of what's recommended by the World Health Organization.

Subsequent trials have shown that higher doses can lessen the chances of developing a cold or reduce its severity if you do come down with one. In a 2007 analysis in Lancet Infectious Diseases, University of Connecticut School of Pharmacy researchers looked at 14 clinical trials involving nearly 3,000 people and found that those who took echinacea had 58 percent less chance of developing a cold. If they did get sick, their colds ended 1.4 days earlier than study participants who didn’t take the herb.

While it’s not clear exactly how echinacea quells colds and flu, studies suggest that it lowers inflammation and helps boost white blood cells that fight infection. According to the American Botanical Council, echinacea is proven safe for all ages. Its sole side effect is a potentially heightened allergy to plants in the ragweed family.

Maria Noel Groves, a clinical herbalist and owner of Wintergreen Botanicals in Allenstown, N.H., believes echinacea is most effective in liquid tincture form. She advises taking ½ to 1 teaspoon every hour at the first onset of cold symptoms, continuing through the duration of the cold. If that sounds like too much of a hassle, studies have shown that daily doses of five to six cups of tea made from 1 gram of the dried herb are effective.

Olive leaf extract

There’s plenty of research on the health benefits of olive oil, but scientists are also discovering that other parts of this Biblical “tree of life” have healing powers. Olive leaves contain a bitter compound called oleuropein, which is believed to help the tree resist disease. Research shows it can do the same thing for humans.

Studies have found that not only does oleuropein have antioxidant, anti-inflammatory and antimicrobial properties, it may actually be able to penetrate infected cells and stop virus reproduction. In a 2001 study published in the Japanese Chemical & Pharmaceutical Bulletin, researchers mixed oleuropein with respiratory and flu viruses in test tubes and concluded that the compound had significant effects on both viruses.

Supplemental olive leaf extract has only been available for about 15 years, so there’s little documentation on side effects. Some manufacturers warn that the product could produce detoxification symptoms that are, ironically, flu-like. Most supplements come in capsule form. Look for products that specifically list oleuropein as an ingredient.

Pelargonium sidoides

This red-flowered South African herb is relatively new to the dietary supplements world, but it packs a potent punch. More than 20 clinical studies of 9,000 patients—including children—show that Pelargonium sidoides extract can treat colds and other upper respiratory tract infections like bronchitis and sinusitis. Researchers believe it does this by protecting cells from being destroyed by viruses and by stimulating immunity. 

A 2007 study published in the journal Explore analyzed 103 adults with cold symptoms who received either the herbal extract or a placebo. After 10 days, 79 percent of the P. sidoides group was clinically cured, compared to 31 percent of those taking the placebo. They also experienced 1.3 fewer sick days at work than the placebo group. 

Research shows that P. sidoides is safe for all ages. The only side effect is mild gastrointestinal upset in about 4 percent of people.