Alzheimer's disease (AD) is commonly associated with behavioural changes such as agitation. Severe agitation is important to treat because it not only increases progression of AD and physical health problems (increased falls and weight loss), but it also decreases quality of life and increases caregiver stress. Currently prescribed treatments (i.e., antipsychotics) for agitation in AD do not work in everybody and when they do work the effect is small and they increase risk of harmful side effects, including death. As a result, there is an urgent need for safer medication options. The cannabinoid nabilone (Cesamet®) can now be prescribed in capsule form for appetite and pain killing effects. Nabilone's calming effects may benefit those with agitation, and help the weight loss and untreated pain frequently associated with agitation. Through a clinical trial, we hope identify the benefits of nabilone in the treatment of agitation in AD.Our objective is to determine whether nabilone is an efficacious and safe treatment for agitation, as well as having benefits for pain and weight loss. This will be a 14 week clinical trial (participants take nabilone for 6 weeks, placebo for 6 weeks (order randomized) with 1 week between treatments). We will assess and compare agitation, weight, pain, memory, behaviour and safety.Nabilone is a new class of medication that may be a safe and effective treatment for agitation in AD, with added benefits on appetite and pain. Reducing these symptoms would increase quality-of-life and reduce caregiver stress.