Nearly three-quarters of prescription drug users in the US say they would be “very concerned” if the medication they had been prescribed was switched, without their doctor’s notice, to a different product approved to treat the same condition, reports the National Consumers League (NCL).

One in five also said they would be concerned even if their doctor did know about the switch, according to the survey, which was conducted to examine consumer views of therapeutic substitution - the dispensing by a pharmacist of a different product from the same therapeutic class as the drug prescribed by a doctor.

Therapeutic substitution - which is not the same as generic substitution - is a cost-saving option for health insurers as it enables pharmacists to supply a cheaper drug than that written on the prescription form. The NCL reports that while pharmacists are more likely to support the practice as a way to save money and optimize patient care, doctors tend to have concerns over the implications for patient safety. In some cases, the substitution can be beneficial or inconsequential, but in others - especially in treatment of epilepsy, mental health and cardiovascular problems - it can be less effective or pose dangers, especially if done without the knowledge of the consumer or prescribing physician.

“For some conditions and treatments, it may make good financial or medical sense to swap out one prescription for another,” said NCL executive director Sally Greenberg. “But, as consumers reported in our survey, it’s essential for them to be a part of this process, to know their doctor is aware and supportive of the switch, and to feel confident that their health and treatment - not financial incentives - are top priority,” she added.

Only 19% of patients told the survey that they would consider switching to a different medication if their insurer wrote to them recommending this change, but 71% said that receiving such a letter would “inspire” them to “have a conversation with their doctor about a less expensive alternative.”

Also, 68% of prescription drug users said they were opposed to insurance companies offering incentives to physicians for switching patients to lower-cost alternatives, and 73% said they did not agree with insurers offering such incentives to pharmacists.

"Without transparency, therapeutic substitution could introduce efficacy or safety issues, including unknown drug interactions and potentially serious health consequences,” said Ms Greenberg.