Inclusion Criteria:

1. Ongoing analgesic therapy with either oxycodone hydrochloride (OxyContinâ) or morphine sulfate (MS Continâ) every 12 hours for cancer pain.
2. Eligible subjects will be ³ 18 years of age with a diagnosis of cancer and an estimated survival of greater than six months.
3. Subjects must be on a stable dose of opioid medication for at least 2 weeks before enrollment.
4. Current other analgesic medications will be maintained during the study. The subject must have been on a stable medication regimen for at least 2 weeks.

5. The following laboratory parameters documented within 45 days prior to study entry:

   • Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) £ 5 X upper limit of normal (ULN)
   • Total bilirubin £ 2 X ULN
   • Creatinine £ 2.0 mg/dL (177 µmol/L)
6. All men and women in this study must agree to use adequate birth control during this study. Acceptable barrier birth control methods are a male condom, female condom, diaphragm, or intra-uterine (IUD).
7. All women of reproductive potential (who have not reached menopause or undergone hysterectomy, oophorectomy, or tubal ligation) must have a negative urine b-HCG pregnancy test performed before initiating the protocol-specified medication.
8. Prior history of use of marijuana. Subjects must have smoked marijuana on at least 6 occasions in their lifetime prior to enrollment.
9. Able to understand and follow the instructions of the investigator, including completing the pain intensity rating scales.
10. Karnofsky Performance Score >60.
11. Able and willing to provide informed consent.

Exclusion Criteria:

1. Severe coronary artery disease, uncontrolled hypertension, cardiac ventricular conduction abnormalities, or orthostatic mean blood pressure drop greater than 24 mmHg, severe chronic obstructive pulmonary disease.
2. History of renal or hepatic failure.
3. Evidence of hepatic, hematological or renal dysfunction based on judgment of physician.
4. Active substance abuse (e.g., alcohol or injection drugs).
5. Use of smoked marijuana within 30 days of enrollment verified with a urine THC level.
6. Neurologic dysfunction or psychiatric disorder severe enough to interfere with assessment of pain or sensory systems.
7. Current use of smoked tobacco products or a confirmed cotinine level.
8. Women who are pregnant or breast-feeding may not take part in this study.
9. Unable to read or speak English.