Becky Stocum of Painesville, Ohio, grew up when coffee was considered strictly an adult beverage, almost on a par with alcohol.

"I wasn't allowed to drink coffee until I was 21," she said. "The parent mentality was 'You're growing and you don't want to put it in your body — it stunts your growth.'"

It bothers her now that she has trouble keeping caffeine, coffee's best-known ingredient, from her son, Zach. A junior in high school, he's an athlete who puts caffeine on his training table via energy drinks.

"I don't like it," she said. "This is a young body, and those chemicals have an impact on your body and your psyche."

Like other parents, she has seen effects including sleeplessness, jitteriness and bursts of anger, as America's favorite drug reaches younger users in bigger doses and more ways.

Sweetened coffee designer drinks aim at the youth market, as do shelves of energy drinks carrying names like Red Bull, Jolt, Shock Wave, Monster Energy, Full Throttle and Rockstar Juiced. One drink, Bawls, also has a line of highly caffeinated candy and frozen SnoBawls. Caffeine laces Sumseeds sunflower seeds and new Snickers Charged, "with an added boost to help get you through the day."

"It's a new area of concern because more products are coming to market," said Laura Jeffers, a Cleveland Clinic pediatric dietician. "It is reaching younger and younger people. They're using it as something that'll help them be more attentive when actually, if they intake it in high amounts, it wouldn't be healthy. Parents should be aware."

Caffeine, a stimulant used by an estimated 90 percent of the world's population, promotes alertness by interacting with brain receptors. It carries other known and suspected benefits.

A recent study in the journal Neuroscience found that a coffee regimen prevented memory impairment in mice that were genetically programmed to develop Alzheimer's disease. Another recent study, in the International Journal of Cancer, suggested that coffee might protect against kidney cancer.

Research with female college students found that caffeine seemed to lessen muscle pain the day after a challenging workout. Earlier studies found reduced rates of liver disease among people who drink more than two cups of coffee a day; that heavy coffee drinking can cut the risk of the most common form of diabetes; and that coffee provides more of the antioxidants that fight cancer, heart disease and aging than do any other food or beverage in the American diet.

But all the effects aren't good. A study published in January in the American Journal of Obstetrics and Gynecology warned that women who drink two or more cups of coffee a day during pregnancy — about 200 milligrams of caffeine — run twice the risk of miscarriage as those who avoid caffeine. Britain's Food Standards Agency commissioned a study, due this year, after other studies showed caffeine was associated with higher risk of miscarriage and lower birth weight.

Other scientists in the United Kingdom reported in The Lancet medical journal that food additives including caffeine can cause behavioral problems among children.

The caffeine in two or three cups of coffee a day — 200 to 300 milligrams — is roughly equivalent to two standard containers of energy drinks and not considered harmful for most adults. But caffeine can cause anxiety, irritability, anxiety, muscle tremors, sleeplessness, headaches, nausea, diarrhea and abnormal heart rhythms.

Research at Johns Hopkins University in Baltimore found that caffeine altered mood and behavior in children — producing an increase in wakefulness and generating feelings of energy and sociability in low dosages, but generating anxiety, tension and insomnia in higher doses, said Mary Beth Kavanaugh, a registered dietician and instructor at the Case Western Reserve University School of Medicine.

The moderate dose in several cans of caffeinated soft drinks raised blood pressure significantly in children, she said, while decreasing heart rate.

"But there haven't really been a lot of studies done," she said. "The effects are dependent upon the weight of the individual, and children have a much lower body weight."

There are no official recommendations on caffeine in the United States because experts say there is not enough data. In Canada, the government recommends caffeine consumption based on age: no more than 45 milligrams a day for 4- to 6-year-olds, 85 milligrams per day for 10- to 12-year-olds, and 300 milligrams (the amount in two to three cups of brewed coffee) for adults.

Dr. Allison Brindle, a Cleveland Clinic pediatrician, said she sees the effects in her practice, especially headaches, insomnia and jitteriness.

"There's no reason for a child to be drinking caffeinated products," Brindle said.

Here's a look at some drinks with the highest caffeine content:

ENERGY DRINKS, SOFT DRINKS (per 12-ounce can)

Powershot: 1,200 mg

Rockstar Zero Carb: 180 mg

Rip It: 150 mg

Red Bull: 115 mg

SoBe No Fear: 130.56

AMP: 112 mg

Full Throttle: 100 mg

Bawls: 80 mg

Jolt: 71.2 mg

Vault: 70 mg

Diet Pepsi Max: 69 mg

Mountain Dew: 55 mg

Pepsi One: 55 mg

Mello Yellow: 52.8 mg

Surge: 52.5 mg

Battery: 46.7 mg

Coca-Cola/Diet Coke: 45.6 mg

Dr Pepper: 39.6 mg

Pepsi: 37.2 mg

Diet Pepsi: 35.4 mg

RC Cola: 36 mg

Snapple (flavored): 31.5 mg

Nestea Sweet Iced Tea: 26.5 mg

Snapple Sweet Tea: 12 mg

7-Up: 0

COFFEE & TEA (milligrams per 12-ounces)

Brewed coffee (7 ounces): 80-135 mg

Espresso (1.5-2 ounces): 100 mg

Instant coffee (7 ounces): 65-100 mg

Decaf (6 ounces): 3-5 mg

Tea, black (6 ounces): 70 mg

Tea, green (6 ounces): 35 mg

OTHER PRODUCTS

No-Doz (tablet): 100 mg

Excedrin (tablet): 65 mg

Snickers Charged (bar): 60 mg

Anacin (tablet): 32 mg

Dark chocolate (1 ounce): 5-35 mg

Jolt gum (piece): 12.7 mg

Milk chocolate (1 ounce): 1-15 mg

SOURCES: National Soft Drink Association; American Beverage Association; Coca-Cola; Mars Snackfood U.S.; Center for Science in the Public Interest; Erowid.org; thecaffeinepage.com; energyfiend.com)