Intended for healthcare professionals


Placebo controlled trials

BMJ 2014; 348 doi: (Published 21 February 2014) Cite this as: BMJ 2014;348:g1635
  1. Philip Sedgwick, reader in medical statistics and medical education,
  2. Carwyn Hooper, lecturer in medical ethics and law
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

Researchers assessed the efficacy of varenicline (a licensed cigarette smoking cessation aid) in helping users of smokeless tobacco to quit. A double blind placebo controlled parallel group randomised controlled trial study design was used. The intervention was varenicline 1 mg twice daily. Treatment was delivered for 12 weeks, with 14 weeks’ follow-up afterwards. Participants were aged 18 years or more. They were also users of smokeless tobacco who wished to quit and had no abstinence period longer than three months during the year before recruitment. In total, 431 participants were recruited and randomised to varenicline (n=213) or placebo (n=218). All participants were offered brief behavioural support or counselling at the discretion of the investigators.1

The primary endpoint was continuous abstinence for four weeks at the end of treatment (weeks 9-12) confirmed by cotinine concentration. A significantly higher rate of abstinence was reported in the varenicline group compared with placebo (59% v 39%; relative risk 1.6, 95% confidence interval 1.32 to 1.87; P<0.001).

Which of the following statements, if any, are true?

  • a) The placebo is referred to as an active control

  • b) The use of a concurrent control group minimised confounding

  • c) The rate of abstinence in the placebo group (39%) is termed the placebo effect

  • d) The most recent version (2013) of the Declaration of Helsinki precludes the use of placebos in randomised controlled trials


Statement b is true, whereas a, c, and d are false.

Smokeless tobacco is often used by smokers trying to quit because it is considered less harmful than …

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