Pharmacological prevention of migraine

Clarification—In this Clinical Review (BMJ 2011;342:d583, doi:10.1136/bmj.d583), doses of drugs for migraine prevention were presented in a table with the abbreviation “QD,” meaning “once daily,” as defined in the table footnote. To avoid prescribing an overdose, readers should not confuse “QD” with “QDS,” which means “four times a day.” The BMJ will avoid using these acronyms wherever possible.