Opioid antagonists for smoking cessation.
BACKGROUND
The reinforcing properties of nicotine may be mediated through release of various neurotransmitters both centrally and systemically. Smokers report positive effects such as pleasure, arousal, and relaxation as well as relief of negative affect, tension, and anxiety. Opioid (narcotic) antagonists are of particular interest to investigators as potential agents to attenuate the rewarding effects of cigarette smoking.


OBJECTIVE
To evaluate the efficacy of opioid antagonists in promoting long-term smoking cessation. The drugs include naloxone and the longer-acting opioid antagonist naltrexone.


METHODS
We searched the Cochrane Tobacco Addiction Group specialized register for trials of naloxone, naltrexone and other opioid antagonists and conducted an additional search of MEDLINE using 'Narcotic antagonists' and smoking terms in March 2006. We also contacted investigators, when possible, for information on unpublished studies.


METHODS
We considered randomized controlled trials comparing opioid antagonists to placebo or an alternative therapeutic control for smoking cessation. We included in the meta-analysis only those trials which reported data on abstinence for a minimum of six months. We also reviewed, for descriptive purposes, results from short-term laboratory-based studies of opioid antagonists designed to evaluate psycho-biological mediating variables associated with nicotine dependence.


METHODS
We extracted data in duplicate on the type of study population, the nature of the drug therapy, the outcome measures, method of randomization, and completeness of follow up. The main outcome measure was cotinine- or carbon monoxide-verified abstinence from smoking after at least six months follow up in patients smoking at baseline. Where appropriate, we performed meta-analysis using a fixed-effect model (Mantel-Haenszel odds ratios).


RESULTS
Four trials of naltrexone met inclusion criteria for meta-analyses for long-term cessation. All four trials failed to detect a significant difference in quit rates between naltrexone and placebo. In a pooled analysis there was no significant effect of naltrexone on long-term abstinence, and confidence intervals were wide (odds ratio 1.26, 95% confidence interval 0.80 to 2.01). No trials of naloxone or buprenorphine reported long-term follow up.


CONCLUSIONS
Based on limited data from four trials it is not possible to confirm or refute whether naltrexone helps smokers quit. The confidence intervals are compatible with both clinically significant benefit and possible negative effects of naltrexone in promoting abstinence. Data from larger trials of naltrexone are needed to settle the question of efficacy for smoking cessation.
David
S
S
Brown University School of Medicine, Department of Family Medicine, Memorial Hospital of Rhode Island, Providence, Rhode Island, USA. sean_david@brown.edu
Lancaster
T
T
Stead
L F
LF
Evins
A E
AE
D002047:Buprenorphine / Q000627:therapeutic use; D006801:Humans; D009270:Naloxone / Q000627:therapeutic use; D009271:Naltrexone / Q000627:therapeutic use; D009292:Narcotic Antagonists / Q000627:therapeutic use*; D016032:Randomized Controlled Trials as Topic; D012907:Smoking / Q000188:drug therapy*; D016540:Smoking Cessation / Q000379:methods*
D009292:Narcotic Antagonists; D009270:Naloxone; D002047:Buprenorphine; D009271:Naltrexone