Technically/legally it is not a supplement. It is a medical food.
Medical foods and dietary supplements are discrete regulatory classifications and are not interchangeable. The former must be shown, by medical evaluation, to meet the distinctive nutritional needs of a specific, diseased patient population being targeted, prior to marketing. In contrast, dietary supplements are intended for normal, healthy adults and require no pre-market efficacy tests. In addition, medical foods require physician supervision and a prescription. To summarize, medical foods are medical products for a specific nutritional purpose as opposed to dietary supplements which are a consumer product to supplement the diet and maintain good health and regular function.
You can read more here: http://tmedpharma.com/docs/Medical-Foods-by-issacson.pdf
No where on the Sigma-Tau Pharmaceuticals website is VSL#3 Regular or DS referred to as a supplement. It is labeled a Medical Food.
I phoned Sigma-Tau Pharmaceuticals and spoke with both a Customer Care Rep and a Medical Care Specialist. When I told the Customer Care Rep that both Cosco and Target have been known to dispense VSL#3 DS without a prescription, I was told they probably don't know it requires a prescription. I asked if the prescription is legally required ort preferred by the company. That is when the customer Care Rep got the Medical Care Specialist involved. He sounded surprised that I was telling him of two stores that reportedly dispensed VSL#3 DS without a prescription. He stated that no store or pharmacy should be dispensing VSL#3 DS withot a prescription. I also asked him is the prescription legally required or preferred by the company. He stated VSL#3 DS is a medical food that requires a prescription. He also said he would consult with the Regulatory Department. He took my information and said he will get back to me. I forgot, but will ask him next time, if VSL#3 is a medical food that reqires a prescription, why is it only the DS that requires it? Is there a dose "cut off" where it is considered to need a prescription?
I'll post when I hear back from him.