A placebo control is important in studying clinical conditions where there is no known effective therapy. Placebo controls are also desirable in studies where the question is whether smoked marijuana is effective or whether it is equivalent to another drug, and many study designs utilize both placebo and active control groups. This design also allows comparison of marijuana with a standard therapy. If an effective standard treatment exists, there are conditions such as chemotherapy-related nausea and vomiting in which it would be unethical to include a placebo control group. In that way, no patient would be deprived of standard effective therapy.
Some investigations address whether an effect is dose related.
This type of design allows for the assessment of the dose range that produces therapeutic effects and the relationship between these effects and dose-related side effects. Although these designs do not exclude the addition of placebo groups, a placebo is often not used because the determination of a positive dose-response curve for an effect provides an internal measure of assay sensitivity. An obvious difficulty with this type of design for smoked marijuana is the inability to standardize dose delivery due to the inherent variability associated with pulmonary administration. One possible design is to compare self-titrated smoking with several fixed doses of THC capsules. Once identified, such patients are randomly assigned to a study drug or control group and are evaluated in a prospective manner.