CBS News Correspondent Vince Gonzales reports that, as the fresh-squeezed alternative is gaining in popularity, some doctors warn juicing up your juice may do more harm than good.
"It's easy and tastes good. It beats going to McDonald's," said customer Jacquey Malteby.
But some customers are getting more than just carrot juice or orange juice. For an extra charge, many stores will add vitamin supplements to drinks.
Jamba Juice is one of the largest chains, with more than 100 stores across the country. Most of their drinks with supplements contain about 100 percent of the recommended daily allowance, or RDA of certain vitamins, a level approved by nutritionists.
But juice bars also offer so-called "megadoses." These drinks contain anywhere from 1,000 percent to 3,000 percent the RDA of various vitamins.
Dr. Carol Koprowski of USC's School of Medicine took a look at the menus of some of California's most popular juice bars and said megadoses are not as good as they seem.
"If they are getting more than what they need, you are dealing with water soluble vitamins, they are eliminated via the urine, and so you end up with very expensive urine."
But Dr. Koprowski says before they leave the body, megadoses of vitamins can do damage. Vitamin C can cause diarrhea, nausea, and even kidney stones.
"When you start taking those large doses, we don't really know. We don't have enough good studies to say that that is a safe thing to do."
Another problem is that even customers who don't buy megadoses think juice with supplements is an alternative to a healthy diet.
"It's really just a great meal replacement. You can't beat it. You feel full but don't have the weight of eating the food," said Malteby.
But with supplements and juice bars gaining popularity, coffee houses are fighting back.
Now they're offering caffeine drinks that are "chock full of vitamins."
"My recommendation: Go ahead. Go to the juice bar. Have your smoothie. Have your fruit juice. Don't pay extra to have anything else added to it," said Dr. Koprowski.
The surge in supplement sales has attracted the attention of the FDA. The government says it is taking a hard look at the health claims manufacturers make, and a new system has been set up to monitor health problems caused by supplements.
Reported by CBS News Correspondent Vince Gonzales