HSD will handle Shire's consumer campaign around Dementialink.co.uk.
The site, expected to launch in the next couple of months, will offer spouses and carers practical information. The disease awareness and support campaign comes ahead of Alzheimer's Awareness Week in July.
The move is part of Shire's efforts to raise the profile of its Alzheimer's treatment, Reminyl XL.
Dementia has become a hugely controversial area, with the National Institute for Health and Clinical Excellence recently rejecting calls from patient groups for certain Alzheimer's drugs to be made available on the NHS for early stage sufferers.