Concerns have been raised about the links between pharmaceutical firms and charity patient groups by the body that advises the NHS on which drugs to use.
The drugs are reserved for those with moderate Alzheimer's
Sir Michael Rawlins, chairman of the National Institute for Health and Clinical Excellence, said charities had to be wary of pharmaceutical donations.
And he urged charities to question the cost of drugs more.
But patient groups said there were strict guidelines covering such donations by the drugs industry.
Sir Michael said: "Patient organisations need to think very carefully about why pharmaceutical companies are giving them money and they have to make sure they are not beholden to a pharmaceutical company.
"I have yet ever to hear a patient organisation criticise a price of the drug.
"When they do that they will come into their own."
Sir Michael refused to name individual groups
The subject of drug firm donations to patients groups and charities is a sensitive issue.
Several groups, although not all, accept donations from drug firms.
Most of those that do have codes of conduct setting out what those donations can and cannot be used for - most are restricted to funding education purposes than for campaigning.
The Alzheimer's Society is involved in legal action along with Eisai and Pfizer against NICE over the decision to restrict the use of Alzheimer's treatments.
The group has accepted money from both companies.
But a spokeswoman pointed out that drug firm donations account for less than 1% of its income.
She said the society's challenge was being done independently of the drug firms and added donations were never used to fund campaign activity.
Breast Cancer Care, which pushed for NICE to approve the so-called breast cancer wonder-drug Herceptin, has received money from its maker Roche.
A spokeswoman said any drug industry donations were always used for "impartial patient information".
She added it was important there was a dialogue between patient groups and drug companies and she agreed cost was something that needed to be debated.
"The cost of drug is clearly becoming a major factor in the potential for cancer treatment and must be addressed."
And the Association of the British Pharmaceutical Industry denied there was anything wrong with such donations.
"Patient groups and companies have a shared interest. When they work together it is in the patients' interests, usually to do with education programmes or disease awareness.
"Any involvement has to be declared by the company so it is quite transparent."