BMJ 1999;318:1579-1584 ( 12 June )

Papers

Oral contraceptives and myocardial infarction: results of the MICA case-control study

Nicholas Dunn, senior research fellow, a Margaret Thorogood, reader in public health and preventive medicine, b Brian Faragher, senior lecturer, c Linda de Caestecker, consultant in public health medicine, d Thomas M MacDonald, professor of clinical pharmacology and pharmacoepidemiology, e Charles McCollum, professor of surgery, f Simon Thomas, senior lecturer, g Ronald Mann, director. a

a Drug Safety Research Unit, Bursledon Hall, Southampton SO31 1AA, b London School of Hygiene and Tropical Medicine, London WC1 6FH, c Department of Organisational Psychology, Manchester School of Management, UMIST, PO Box 88, Manchester M60 1QD, d Department of Public Health, Greater Glasgow Health Board, Dalian House, PO Box 15327, Glasgow G3 8YU, e Medicines Monitoring Unit, Department of Clinical Pharmacology and Therapeutics, Ninewells Hospital Medical School, Dundee DD1 9SY, f Department of Surgery, South Manchester University Hospital, West Didsbury, Manchester M20 8LR, g Wolfson Unit of Clinical Pharmacology, University of Newcastle, Newcastle upon Tyne NE2 4HH

Correspondence to: Dr Dunn ndunn{at}dsru.u-net.com

Objectives: To determine the association between myocardial infarction and use of different types of oral contraception in young women.
Design: Community based case-control study. Data from interviews and general practice records.
Setting: England, Scotland, and Wales.
Participants: Cases (n=448) were recruited from women aged between 16 and 44 who had suffered an incident myocardial infarction between 1 October 1993 and 16 October 1995. Controls (n=1728) were women without a diagnosis of myocardial infarction matched for age and general practice.
Main outcome measures: Odds ratios for myocardial infarction in current users of all combined oral contraceptives stratified by their progestagen content compared with non-users; current users of third generation versus second generation oral contraceptives.
Results: The adjusted odds ratio for myocardial infarction was 1.40 (95% confidence interval 0.78 to 2.52) for all combined oral contraceptive users, 1.10 (0.52 to 2.30) for second generation users, and 1.96 (0.87 to 4.39) for third generation users. Subgroup analysis by progestagen content did not show any significant difference from 1, and there was no effect of duration of use. The adjusted odds ratio for third generation users versus second generation users was 1.78 (0.66 to 4.83). 87% of cases were not exposed to an oral contraceptive, and 88% had clinical cardiovascular risk factors or were smokers, or both. Smoking was strongly associated with myocardial infarction: adjusted odds ratio 12.5 (7.29 to 21.5) for smoking 20 or more cigarettes a day.
Conclusions: There was no significant association between the use of oral contraceptives and myocardial infarction. The modest and non-significant point estimates for this association have wide confidence intervals. There was no significant difference between second and third generation products.


Key message

  • There is no evidence of a difference between second and third generation oral contraceptives on risk of myocardial infarction

  • There is no significantly increased risk of myocardial infarction in users of oral contraceptives

  • Of women aged under 45 years who suffered a myocardial infarction, 87% were not taking any oral contraceptive

  • Of women who suffered myocardial infarction, 88% had one or more known cardiovascular risk factors

  • Young women who wish to preserve cardiovascular health should be advised to stop smoking, above all else



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Rapid Responses:

Read all Rapid Responses

Large selection bias likely
Rosemary Kirkman
bmj.com, 23 Jun 1999 [Full text]
MICA paper on oral contraceptives
Paul O'Brien
bmj.com, 12 Jul 1999 [Full text]
Re: Large selection bias likely
Nicholas Dunn
bmj.com, 17 Jul 1999 [Full text]
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