The purpose of this study is to determine the effective dose range and to demonstrate a non-effective dose range of Sativex in patients with advanced cancer, who experience inadequate pain relief even though they are on optimized chronic opioid therapy.

Inclusion Criteria:

• The patient has advanced active cancer for which there is no known curative therapy.
• The patient is able (in the investigators opinion) and willing to comply with all study requirements.
• The patient has a clinical diagnosis of cancer related pain, which is not wholly alleviated with their current opioid treatment.
• The patient is receiving a sustained release (SR) fixed dose of opioid therapy (excluding Methadone). N.B. The opiate therapy must be Step III according to the WHO analgesic ladder.
• The patient is willing to continue to take their regular daily baseline opioid regimen (SR) at the same dose, throughout the duration of study.

Exclusion Criteria:

• The patient should be excluded from entering study if they have received or are due to receive during the study period; chemotherapy, hormone therapy or radiotherapy, which, in the opinion of the investigator will affect their pain.
• The patient is currently using two or more types of break-through opioid analgesia (IR).
• Any history or immediate family history of schizophrenia, other psychotic illness, severe personality disorder or other significant psychiatric disorder other than depression associated with their underlying condition.
• Any known or suspected history of a diagnosed dependence disorder, current heavy alcohol consumption, current use of an illicit drug or current non prescribed use of any prescription drug.
• The patient has poorly controlled epilepsy or recurrent seizures (i.e. at least one year since last seizure).
• The patient has experienced myocardial infarction or clinically relevant cardiac dysfunction within the last 12 months or has a cardiac disorder that, in the opinion of the investigator would put the patient at risk of a clinically relevant arrhythmia or myocardial infarction.