Congress's ungainly drug statute 21 U.S.C. §841, provides in paragraph (b)(1)(C) for a life sentence if death or serious bodily injury results from using the drugs. In U.S. v. Hatfield, Judge Posner of the Seventh Circuit has this to say about causation:

Causation is an important issue in many cases in a variety of fields of law and has been so for centuries. Yet it continues to confuse lawyers, in part because of a proliferation of unhelpful terminology (for which we judges must accept a good deal of the blame). In the space of three-and-a-half pages in the government's brief, we find the following causal terms: proximate cause, actual cause, direct cause, but-for causation, contributing causation, contributory causation, significant causal connection, sole cause, factor in the victims' injuries, concurrent cause, meaningful role, possible cause, remote cause, and cause in fact. Black's Law  Dictionary (8th ed. 2004) lists 26 terms in the entry for "cause." The prosecutor was unable at oral argument satisfactorily to differentiate or explain the causal terms listed in his brief, or the three causal terms added to the instruction--"a factor that resulted in," "primary cause," and "played a part."

In the end, it was a mistake for the government to try to explain too much by pulling language out of appellate opinions and putting it in a jury instruction. "All that would have been needed to satisfy [the defendant's objection to the instruction] was to eliminate the addition to the statutory language, which was a good deal clearer than the addition and probably clear enough. Elaborating on a term often makes it less rather than more clear (try defining the word 'time' in a noncircular way)...."