Many recommended drug doses are higher than necessary, for two reasons. Drugs are often introduced at a dose that will be effective in around 90% of the target population, because this helps market penetration. Doses are also partly determined by an irrational preference for round numbers. The dose excess due to such digit preference may be as much as 70% of the correct dose and on average is probably 25%. Needlessly high doses are bound to cause avoidable unwanted effects in a proportion of patients. Rigorous methods must be used to determine the doses recommended and the amount of drug to be put into a tablet or other dosage form.