Tanner v. United States, 483 U.S. 107 (1987), was a United States Supreme Court case in which the Court held that juror testimony could not be used to discredit or overturn a jury verdict, even if the jury had been consuming copious amounts of alcohol, marijuana, and cocaine throughout the course of the trial.

After the defendant was found guilty of mail fraud, his attorneys filed several motions after they discovered that seven of the jurors drank alcohol during the noon recess.

[1] Of the other three, one said that, on several occasions, he observed two jurors having one or two mixed drinks during the lunch recess, and one other juror, who was also the foreperson, having a liter of wine on each of three occasions.

[2] One juror sold one-quarter pound (110 g) of marijuana to another juror during the trial, and took marijuana, cocaine, and drug paraphernalia into the courthouse.

[4] The court noted that "the near-universal and firmly established common-law rule in the United States flatly prohibited the admission of juror testimony to impeach a jury verdict".