Conventional wisdom has been bullish regarding the potential profits from investing in commercial marijuana businesses, now considered legal in several states but not under federal law. There have even been glossy brochures from consulting firms, offering the lure of potential billions in sales for the savvy investor.

But there remain very substantial obstacles to those glittering inducements. A recently-published advisory from American Bar Association analyzed the malpractice liability for physicians who recommend “medical marijuana,” warning: