Souvenaid, which costs £3.49 per 125ml bottle, contains a cocktail of the nutrients needed to build new connections in the brain. Its makers, Nutricia, claim the once-a-day product, which goes on sale in the UK today, has been clinically shown to improve memory in mildly affected patients.
But Professor Clive Ballard, director of research at the Alzheimer's Society, urged people to spend their money elsewhere.
"People shouldn't get excited that an off-the-shelf drink is going to transform the lives of people with dementia. For many older people with dementia where finances might be tight, people are probably much better off putting their money towards good-quality care or taking part in exercise," he said.
Charity Alzheimer Scotland voiced concerns over the cost of the nutritional supplement, and called for it be made available through the NHS.
Its spokesman said: "We do not understand why further economic pressure should be placed on individuals, couples and families who are already likely to be experiencing significant financial hardship while coping with dementia.
"This treatment will cost £1000 a year; in the absence of proper medical monitoring, there is no real way to judge its effectiveness.
"For those who are not able to afford this product, we do not think that they should worry, as it is not as effective as prescribed drug treatments that most people with mild Alzheimer's disease can get free.
"We believe that people should think carefully before deciding to buy it, and talk to their GP."
Dementia affects 86,000 people in Scotland, more than half with Alzheimer's disease.
Souvenaid is said to be the result of more than a decade of research into the nutritional needs of people with early Alzheimer's. A key feature of the disease is the loss of synapses, or connections in the brain, which are vital to memory.
People with Alzheimer's lack certain nutrients necessary for synapse-building, it is claimed. The drink will be sold in pharmacies throughout England, Scotland and Wales, and via the Souvenaid website.