Nothing, it seemed, could get Cody Cifani to cut back on his daily energy drinks. Then the Texas 15-year-old had two espresso shots, followed by three Monster drinks, to pump himself up for his job at a car shop. Instead of the expected rush, he felt sick.

“It was a pounding feeling in my entire head,” he said. “I was extremely fatigued, and I didn’t want to move. It felt like a really bad crash. I felt really bad the entire day and had stomach pains when I woke up.”

While energy drinks may look and taste like sodas, they are packed with significantly higher levels of caffeine. That may sound benign, but doctors note that caffeine is a stimulant that can, in excess, lead to convulsions, irregular heartbeat and, in extreme cases, death. A report from the Drug Abuse Warning Network, a U.S. public health surveillance system that monitors possible drug-related deaths and visits to hospital emergency rooms, noted 20,783 visits related to energy drinks in 2011 alone.

That’s why, even as makers of the drinks say their products are safe and are not marketed to children, some health experts are warning parents to be wary.

The U.S. Food and Drug Administration says that sodas, which are classified as beverages, cannot contain more than 71 milligrams of caffeine per 12 ounces. (For comparison, a Coca-Cola Classic has 30 to 35 milligrams per 12 ounces, and a 16-ounce McDonald’s coffee has 100 milligrams, according to the Mayo Clinic.)

If energy drinks are labeled as dietary food supplements, as some are, the FDA doesn’t restrict the caffeine. Monster’s Worx Energy contains 200 milligrams of caffeine in 2 ounces, Coca-Cola’s NOS energy 260 milligrams in 16 ounces, and Rockstar energy 240 milligrams in 16 ounces.

Too, too much

That’s way more stimulant than Dr. Marcie Beth Schneider, an adolescent pediatrician in Greenwich, Conn., believes any child should have.

She recently testified before the Senate Commerce Committee about her concerns.

“We don’t think energy drinks should ever be consumed by kids because they cause a whole host of medical side effects,” she said in a phone interview. “They raise heart rate and blood pressure, cause rhythm disturbances and anxiety, gastrointestinal upset and sleeplessness, and we don’t know what those things do to a developing neurological and cardiovascular system.”

Experts generally agree. The National Collegiate Athletic Association prohibits the drinks for student-athletes. In June, the American Medical Association recommended banning the marketing of energy drinks for those younger than 18.

The 14 energy-drink companies that issued statements at the Senate meeting said that they do not market their product to children and teens. A statement from Janet Weiner, chief operations officer and chief financial officer of Rockstar, questioned the Drug Abuse Warning Network’s report, noting that the reported number of 20,000 ER visits was a tiny percentage of the total number of ER visits, and that “most of the ER visits did not require further treatment because they were not serious.” She added, “Coffee and tea, rather than energy drinks, are the most significant sources of caffeine for Americans, including teens and children.”

Accusations and lawsuits

As the drinks’ popularity has grown — they are a $12.5 billion business, according to Forbes — there have been attention-grabbing incidents.

As of October, the Federal Drug Administration was investigating five deaths and one nonfatal heart attack by people consuming Monster. Two wrongful-death lawsuits have been filed against Monster since 2012, one from the family of Anais Fournier of Maryland, a 14-year-old who died in 2011 after consuming two 24-ounce drinks in a 24-hour period. Another, filed in June, is from Paula Morris of California, who blames the death of her son, Alex Morris, 19, on drinking two cans of Monster’s energy drink every day for the three years before he died of cardiac arrest.

Monster Beverage Corp. responded last year with a statement maintaining that its product is safe and in full compliance with all laws and regulations.

The Associated Press has reported that Monster’s lawyer, Daniel Callahan, said the company hired a team of physicians to review medical records. The team found no medical evidence from an autopsy report that said caffeine toxicity was a factor, which suggests that Anais Fournier died of natural causes brought on by her pre-existing heart conditions, Callahan said.

Schneider said that energy-drink companies like to compare the caffeine in their products to that in coffee, but that energy drinks have additional ingredients that magnify the effects of the stimulant, such as taurine and guarana. She said not enough kids are aware of how much stimulant they may be consuming in a day, particularly if they also drink coffee, use medication for attention-deficit disorder or take an over-the-counter drug that helps them pull all-nighters.

A change of attitude

Dr. Michelle Fowers, a pediatrician at Baylor Medical Center at Irving-Coppell in Texas, said she thinks that education can help kids kick the energy-drink habit.

“The kids see someone they look up to with a can of Red Bull in his hands and that makes it OK,” she said. “They think it’s not alcohol, it’s not hard drugs, it’s not so bad. But caffeine is a drug. It can be harmful, and it is addictive. Once kids start taking it, they want more, and they will feel the pain of withdrawal when they stop.”

Dr. Akram Khan said he’s learned to ask patients who report a rise in palpitations and chest pains about their consumption of energy drinks. He is a cardiologist and medical director for Cardiac Center of Texas in McKinney and director of preventive medicine at Medical City. The drinks have become ubiquitous, he said, even showing up in his physician lounge.

“The kids drink it like water, and it’s like a time bomb,” he said. “It can be fatal if you have an underlying condition, and it can also damage a healthy heart.”