title: Headaches and the treatment of blood pressure: results from a meta-analysis of 94 randomized placebo-controlled trials with 24,000 participants.
abstract: BACKGROUND
  Uncertainty exists over whether blood pressure-lowering drugs prevent headache.
  
  
  RESULTS
  A meta-analysis was carried out of the 94 randomized placebo-controlled trials of 4 different classes of blood pressure-lowering drugs (thiazides, beta-blockers, ACE inhibitors, and angiotensin II receptor antagonists) in fixed doses in which data on headache were reported. There were 17,641 participants who were allocated blood pressure-lowering drugs and 6603 who were allocated placebo. Treatment lowered systolic and diastolic blood pressures by 9.4 and 5.5 mm Hg, respectively, on average. One third fewer people on average reported headache in the treated groups (8.0%) than the placebo groups (12.4%) (odds ratio, 0.67; 95% CI, 0.61 to 0.74; P<0.001). About 1 in 30 treated persons benefited by having headache prevented. The prevalence of headache was reduced (P<0.001) in trials of each of the 4 classes of drugs.
  
  
  CONCLUSIONS
  Our results show that blood pressure-lowering drugs prevent a significant proportion of headaches. That this effect is seen with pharmacologically unrelated classes of drugs indicates that it is likely to be due to the reduction in blood pressure per se, the only recognized action that the drugs have in common. This in turn indicates that high blood pressure is a cause of headache, but this conclusion is not supported by observational studies of blood pressure and headache. The uncertainty over whether high blood pressure causes headache does not, however, detract from the practical benefits of the use of blood pressure-lowering drugs in preventing headaches and cardiovascular disease.
authors.affiliation: Centre for Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, Barts, UK. m.r.law@qmul.ac.uk
authors.forename: Malcolm
authors.initials: M
authors.lastname: Law
authors.forename: Joan K
authors.initials: JK
authors.lastname: Morris
authors.forename: Rachel
authors.initials: R
authors.lastname: Jordan
authors.forename: Nicholas
authors.initials: N
authors.lastname: Wald
mesh_terms: D000959:Antihypertensive Agents / Q000009:adverse effects*; D006261:Headache / Q000139:chemically induced*; D006801:Humans; D006973:Hypertension / Q000188:drug therapy*; D010919:Placebos; D016032:Randomized Controlled Trials as Topic
chemical_list: D000959:Antihypertensive Agents; D010919:Placebos