Inclusion Criteria:

- > 18 years of age

- Experiences episodes of breakthrough pain which respond to opioid therapy

- Controlled baseline pain

- Cognitive status sufficient for accurate completion of assessment form

- Willing to provide written informed consent

- Ability to hold a volume of 1 cc of water under the tongue for 5 minutes

Exclusion Criteria:

- Currently or has received methadone during the previous week

- Recent history of substance abuse

- Severe respiratory impairment or other contraindications to opioids

- Recently received therapies that had the potential to alter pain intensity or
response to analgesics

- Symptomatic anemia