CC 2376 defines usable amount as an amount in a quantity sufficient to be used as a controlled substance, claiming that there is no requirement that the amount be enough to affect the user. However, the California Supreme Court has made it clear that a very small amount of a controlled substance is relevant to the element of knowledge: “. . .the form, not the purity, of the substance, is most pertinent to the question of knowledge. But purity may in some cases also be relevant. If, for example, the substance was found in a package of talcum powder, testimony that it contained only a microscopic amount of cocaine might be relevant to defendant’s knowledge of the presence of the contraband.” (People v. Rubalcava (1993) 6 Cal. 4th 62.)
Thus, the jury should be told that a small amount of the controlled substance may show that the defendant lacked knowledge that contraband was present:
The lack of the defendant’s knowledge of the presence of a controlled substance may be shown by the fact that the amount of the controlled substance suggests that the defendant was unaware of the presence of the controlled substance.
So long as there is substantial evidence supporting a defense such as the Compassionate Use defense, on request of the defense the court must give an instruction on that defense. (People v. Panah (2005) 35 Cal. 4th 395, 484.)