The effect of cigarette smoking on drug metabolism in the liver and placenta: the use of cotinine in verifying smoking status

Placental and hepatic xenobiotic-metabolising activities were studied in smokers and non-smokers, who were classified by anamnestic interview, plasma thiocyanate and plasma cotinine determinations. Plasma thiocyanate assay is inadequate in the classification of smokers and non-smokers. Plasma cotinine levels reflect more accurately the smoking status. The anamnestic smokers remained smokers and several self-declared non-smokers proved to be smokers. On the basis of plasma cotinine determination all real smokers had higher 7-ethoxyresorufin 0-deethylase (ERDE) activities measured either in placental microsomes or liver biopsy homogenates than non-smokers. Classification based on plasma cotinine levels showed a statistically significant (P less than 0.001) difference between smokers and non-smokers in liver homogenate ERDE activity. However, cotinine levels did not correlate with any of the xenobiotic-metabolising activities tested. An objective biochemical marker, such as cotinine determination seems to be necessary when evaluating the effect of smoking on drug metabolism in man.     

The effect of smoking on nicotine metabolism in vivo in man

Nicotine and a basic metabolite, cotinine, were determined in the urine by gas-liquid chromatography after intravenous administration of (—)-nicotine hydrogen (+)-tartrate to groups of male and female smokers and non-smokers in whom the urine was maintained at an acid pH. The urinary recoveries of nicotine and cotinine from male smokers fell in two groups. One showed a lower recovery of both alkaloids than was seen with male non-smokers. The other showed a similar recovery of nicotine but more cotinine than the male non-smokers. Female smokers excreted less nicotine but more cotinine than female non-smokers. More nicotine but less cotinine was excreted by female non-smokers than by male non-smokers. The results show sex dependent metabolism of nicotine occurs in non-smoking humans and that smoking causes alterations in nicotine metabolism.     

Determination of nicotine and cotinine in human serum and urine: an interlaboratory study

An interlaboratory study aimed at determining nicotine and cotinine in human serum and urine was carried out. 11 laboratories from 6 countries, all experienced in performing nicotine and cotinine determinations in biological fluids by radioimmunoassay (RIA) and/or gas chromatography (GC) were involved. Each of them received 18 serum and 18 urine samples. The specimens were obtained from 8 smokers and 10 non-smokers; 2 samples from non-smokers were spiked with defined amounts of nicotine and cotinine. All the laboratories distinguished perfectly between the smokers and the non-smokers and according to cotinine levels in serum the laboratories ranked the samples with good agreement. There were systematic differences in the absolute values between the laboratories. The ratios of urinary cotinine concentrations between active and passive smokers differed widely from laboratory to laboratory. The reasons for this are not yet known and necessitate further investigation.     

Nicotine exposure can be detected in cerebrospinal fluid of active and passive smokers

A simple, rapid and sensitive liquid chromatography/mass spectrometry (LC/MS) method has been utilized for the quantitative determination of nicotine and its major metabolite cotinine (COT) in human cerebrospinal fluid (CSF) of active and passive smokers. CSF samples from 18 smokers, 15 non-smokers, 15 children, 15 infants, and 9 neonatal were analyzed for nicotine (NIC) and cotinine content. Cotinine levels in the CSF of smokers ranged from 27.3 to 457.1 ng/ml, whereas nicotine levels were considerably lower (6.0–215.1 ng/ml). Cotinine could be detected in 4 of the 15 CSF samples from non-smokers (3.5–30.4 ng/ml), and a few other passive smokers, including neonates from smoking mothers (15.6–81.1 ng/ml). The concentrations of cotinine in CSF samples suggests that nicotine easily passes into the CSF, which makes it an excellent CSF marker for tobacco-smoke exposure.     

Estimation of smoke dosage and mortality of non-smokers from environmental tobacco smoke

This paper shows how biochemical markers can be used to estimate smoke intake from passive smoking to complement epidemiological studies on the health risks and mortality to non-smokers. Using data from slow nicotine infusions given over 1 h, we estimated that the nicotine intake from passive smoking averages about 0.014 mg/h among urban non-smokers leading their usual daily lives. This compares with 0.23 mg/h in a smoke-filled public house, 0.36 mg/h during maximum exposure in an unventilated room, and 1.0 to 1.4 mg nicotine per cigarette taken in by active smokers. Data from several studies on urinary nicotine concentrations and those of cotinine in blood, urine and saliva were collated. The results show that the concentrations in non-smokers averaged about 0.7% (for nicotine) and 0.6% (for cotinine) of the levels found in smokers. From this we estimate that the mortality from passive smoking is about 1000 non-smokers per year in Britain and about 4000 per year in the United States, assuming that the relation of dose to risk is linear.     

Clinical correlation between the consumption of nicotine and cotinine concentrations in urine and serum by competitive enzyme-linked immunosorbent assay

Different negative effects of smoking are known (e.g. postoperative complications), which lead, especially in plastic surgery, to unsatisfactory results. The aim of this study was to examine the appropriateness of a cotinine enzyme-linked immunosorbent assay (ELISA) for routine usage in operative disciplines. By correlation of smoking habits and concentration of cotinine in serum and urine, we tried to ascertain reference values for smokers, passive smokers and non-smokers. The reliability and sensitivity of the cotinine ELISA concerning nicotine exposure need to be proven. 165 (108 men, 57 women) test persons were examined by detecting cotinine in serum and urine by ELISA. The study shows a very good sensitivity, precision and reproducibility of the cotinine ELISA according to the laboratory criteria. The test shows significance of a good differentiation between smokers, passive smokers and non-smokers in urine. In serum, cotinines are excellent to differentiate between smokers and non-smokers/passive smokers. Urine and serum tests demonstrate valid and comparable results.     

Decreased serum cotinine levels in smokers of both tobacco and marijuana as compared with smokers of tobacco only

Serum and salivary cotinine levels were determined in tobacco smokers (n=125) tobacco (n=47) or who smoked both marijuana and tobacco (n=78) as part of a field study of the pulmonary effects of heavy, habitual use of marijuana alone or with tobacco. After adjustment for current daily amount of tobacco use and time since the last tobacco cigarette was smoked, the smokers of both marijuana and tobacco were found to have lower levels of cotinine then those who smoked only tobacco, in serum [258±113 ng/ml (S.D.) and 332±109, respectively; P=0.003] and in saliva (331±170 and 395±170, respectively; P=0.058). Serum cotinine showed a significantly negative relationship to the daily amount of marijuana currently smoked (p=0.026). Possible explanations include inhibition by marijuana component(s) of the enzymes that participate in the conversion of nicotine to cotinine, differences in nicotine absorption patterns between the two groups of tobacco smokers, and acceleration of cotinine metabolism by marijuana smoking. Carefully controlled pharmacokinetic studies, not possible in a large-scale survey such as this one, are required both to confirm the differences in blood cotinine levels observed between the dual smokers of tobacco only and to define more clearly nicotine-marijuana interactions.     

Salivary cotinine levels in human tobacco smokers predict the attentional validity effect size during smoking abstinence

Abstract. Rationale. The link between attention and brain cholinergic neurotransmission is widely accepted. Human chronic tobacco smokers maintain high levels of nicotine in plasma and body tissues and show enhanced attentional orienting and other attentional tasks. Objective. We wished to test whether abstinence from smoking caused levels of the nicotine metabolite cotinine to decline and attentional enhancement to be reduced in a correlated manner. Methods. The levels of salivary cotinine and behavioral performance on a cued target detection task were measured in chronic, adult tobacco smokers over a 5-day abstinence period. Control groups assessed over the same time period include non-smokers, smokers that did not abstain from tobacco, and smokers that abstained for 4 days and smoked on the last day. Results. In all groups with tobacco exposure, the levels of cotinine declined steadily with time after abstinence, reaching near zero levels at day 5. During this period, reaction times declined as well for all groups, due in part to task practice effects. In contrast, the validity effect, which indexes attentional allocation, increased with abstinence and was inversely related to cotinine levels in groups exposed to tobacco. Conclusions. We conclude that 1) nicotine abstinence increases the attentional validity effect, and 2) this increase is indexed by salivary cotinine, and 3) that control levels of attentional performance are achieved after 3–4 days of tobacco abstinence. Electronic Publication     

Effect of cigarette smoking on salivary epidermal growth factor (EGF) and EGF receptor in human buccal mucosa.

The mouth acts as a primary target for cigarette smoke which is associated with several oral diseases and cancer. The present study investigated the effect of cigarette smoking on salivary EGF and the buccal EGF receptor. Samples of whole saliva and buccal biopsy were obtained from 15 healthy volunteers (10 smokers and 5 non-smokers). The smokers smoked 20 or more cigarettes/day for more than 5 years. Salivary cotinine (a major metabolite of nicotine) was determined by radioimmunoassay (RIA). The salivary cotinine level was consistent with the self-reported smoking status (smokers, 106-530 ng/ml saliva; non-smokers, < 2 ng/ml saliva). As compared to the non-smokers, the salivary EGF concentration (determined by RIA) was 32% lower in those smokers whose salivary cotinine level was 250 ng/ml or higher (non-smokers, 2.21 +/- 0.16; smokers, 1.57 +/- 0.09 ng/ml saliva; mean +/- S.E.M., P < 0.01). There was no significant difference in 125I-labeled EGF binding to the buccal receptor between the two groups. However, EGF stimulated the autophosphorylation of a 170-kDa protein band in the sample of non-smokers, but not in the smokers. The immunoblot analysis using anti-EGF receptor antibody indicated that the smoking-related deficiency in EGF receptor autophosphorylation was due to the functional alteration of the receptor proteins. In conclusion, cigarette smoking reduces the salivary EGF level and impairs the function of buccal EGF receptor, which may be associated with the pathology of smoking-related oral disease.     

Lack of effect of cimetidine on cigarette smoking

Summary The efficacy of cimetidine as a treatment that could reduce smoking in heavily dependent smokers has been determined. In a randomised, double-blind, double-crossover experiment, 43 heavy smokers were divided into two groups, one receiving cimetidine 400 mg orally three times a day, and the other receiving placebo for two weeks followed by the alternative treatment (placebo or cimetidine).No significant difference in the mean alveolar carbon monoxide, nicotine or cotinine levels was found between the two treatment groups compared to baseline. Since the alveolar carbon monoxide level reflects the intensity of smoking behaviour, the results suggest that no change in smoking behaviour occurred in the subjects.Contrary to our previous findings that cimetidine decreased the total body clearance of nicotine by 30% in a population of non-smokers, in the heavily dependent smokers, cimetidine did not appear to alter nicotine elimination. One possible explanation for the discrepancy is that tobacco smoking is known to induce nicotine metabolism and the induction might have offset any effect of cimetidine on nicotine elimination.Cimetidine does not appear to be a useful treatment leading to a reduction or cessation of cigarette smoking.     

Nocotine dependence in cigarette smoking: An empirically-based,multivariate model

Nicotine dependence implies a pattern of heavy smoking which is resistant to change, as well as nicotine tolerance, withdrawal, and regulation. The present study attempted to develop a coherent model of cigarette smoking by examining responses on several different measures of nicotine dependence. Twenty-seven habitual smokers filled out questionnaires before and after smoking research cigarettes differing in nicotine content in the laboratory. Plasma continue was used to estimate nicotine intake from usual brand cigarettes outside the laboratory. Subjects in the high cotinine quartile (heavy smokers) were found to be consistently more nicotine-dependent than subjects in the low cotinine quartile (light smokers). Taking all subjects into account, the six measures of nicotine dependence which exhibited significant correlations with plasma cotinine accounted for about half of the cotinine variance in a multivariate, linear-regression model. Multivariate approaches provide additional tools for assessing biobehavioral mechanisms in substance abuse and may lead to the development of more comprehensive and sufficient explanations of smoking than are currently available.     

Varenicline and Nicotine Patch Therapies in Young Adults Motivated to Quit Smoking: A Randomized,Placebo‐controlled,Prospective Study

This study compares the nicotine patch to placebo in young adult light smokers, and the nicotine patch to varenicline in heavy smokers. Volunteer daily smokers were recruited into a randomized, placebo‐controlled study via community media, colleges and the army (aged 18–26 years). Those subjects with light tobacco dependence were randomized to (i) placebo patch (n = 86) and (ii) nicotine patch 10 mg/16 hr for 8 weeks (n = 94), and those with stronger dependence to (iii) nicotine patch 15 mg/16 hr for 8 weeks (n = 51) and (iv) varenicline for 12 weeks (n = 60). The primary outcome variable was self‐reported smoking abstinence at week 12. Secondary outcome variables were self‐reported smoking abstinence at weeks 4 and 26, and self‐reported abstinence verified by saliva cotinine level at week 12. The prevalence of self‐reported smoking abstinence did not differ statistically significantly in light smokers during the follow‐up (week 4: 19.8% for placebo patch and 26.6% for nicotine patch 10 mg/16 hr; week 12: 17.4% versus 23.4%; week 26: 15.1% versus 20.2%), but the groups of heavy smokers differed significantly for 12 weeks (week 4: 19.6% for nicotine patch 15 mg/16 hr and 73.3% for varenicline, p < 0.001; week 12: 15.7% versus 36.7%, p = 0.018). This statistically significant difference did not endure for the entire follow‐up (week 26: 9.8% versus 18.3%, p = 0.280). However, saliva cotinine verified abstinence at week 12 did not support self‐reported abstinence. Varenicline may be more effective than the nicotine patch as a smoking cessation pharmacotherapy among young adult heavy smokers in the short‐term.     

Stress and arousal rhythms in cigarette smokers,deprived smokers,and non-smokers

Feelings of stress and arousal were assessed in sedative smokers (N = 26), stimulant smokers (N = 14), nicotinedeprived smokers (N = 14), and non-smokers (N = 22). The self-rating questionnaire was completed every 2 hours, from waking until late evening. Feelings of anxiety/stress decreased over the day in non-smokers, and both groups of smokers, but increased in deprived smokers (group × time interactions: p < 0.001). This demonstrates the anxiogenic effects of nicotine deprivation, and confirms that one major reason for smoking is to avoid the deleterious effects of nicotine deprivation. While average daily stress levels did not differ significantly between smokers and non-smokers, both groups of smokers started the day with higher stress than non-smokers, but ended the day with slightly lower stress (group × time interactions: p < 0.001). Thus the gradual accumulation of nicotine does have anxiolytic effects. The arousal findings were complex, with different circadian patterns found across all four groups.     

Nicotine and cotinine levels in body fluids of habitual smokers who committed suicide]

Suicide is a serious social problem because over 30,000 people commit suicide every year since 1998 in Japan. Cigarette smoking is associated with a higher risk for suicide and attempted suicide. We determined nicotine and cotinine levels in blood and urine of 104 deceased individuals (21 suicides and 83 non-suicides). Of the 21 suicides, 16 (76.2%) were smokers; the smoking rate in non-suicides was 41.0% (34 persons). Average levels of nicotine and cotinine in blood were significantly higher in the suicide smokers than in the non-suicide smokers (nicotine: 95.6 +/- 43.9 ng/ml vs. 28.0 +/- 15.2 ng/ml, p < 0.0001; and cotinine: 385 +/- 220 ng/ml vs. 229 +/- 181 ng/ml, p < 0.02). Average levels of nicotine and cotinine in urine also significantly higher in the suicide smokers than in the non-suicide smokers. There were eight patients with psychiatric diseases such as schizophrenia, depression and alcohol dependence. Of the eight patients, four were suicide smokers; only a person used antipsychotics. Thirty-one alcohol-intoxicated decedents consisted of 8 suicides (8 smokers) and 23 non-suicides (17 smokers). Our data demonstrate that there is a marked increase in cigarette smoking in habitual smokers with psychiatric disorders before committing suicide. Quantitatively monitoring the severity of stress using blood nicotine level may enable physicians more objectively to find out nicotine dependents who are in the state of an imminent suicide attempt and timely to administer medical treatment for preventing suicide.     

Correlation between urinary nicotine, cotinine and self-reported smoking status among educated young adults

The objective of this study was to correlate, differentiate and validate the self-reported smoking status of educated young adults with urinary biomarkers (i.e. nicotine and cotinine). Freshmen students were recruited on voluntary basis. They filled-up self-administered questionnaire and their urine samples were collected for analysis. The urinary nicotine (UN) and cotinine (UC) were measured by gas chromatograph-mass spectrometry. Smokers, non-smokers and ex-smokers were found to be both significantly correlated and different in their UN and UC levels. UC level of 25ng/ml was the optimal cut-off to differentiate smokers from non-smokers. Using this cut-off value, the prevalence of smoking among the students was found to be higher (15.4%) than the self-reported data (14.3%). UC is useful in validating individual recent smoking history and the cut-off could serve as a marker for assessing the clinical impact of smoking and environmental tobacco smoke (ETS) exposure on human health.     

Verification of smoking history in patients after infarction using urinary nicotine and cotinine measurements

Urinary concentrations of nicotine and its major metabolite cotinine were measured in volunteers whose smoking habits were known to test the reliability of the measurements as indicators of current smoking. In the non-smokers detectable concentrations were always below the confidence limits set for the method, while in smokers the concentrations were always above these limits. After subjects stopped smoking cotinine appeared in the urine for longer than nicotine and was still detectable at least 36 hours after the last cigarette had been smoked. When this method was used to verify the smoking histories given by patients attending an infarction clinic it was estimated that 46-53% of previous smokers had actually stopped smoking compared with the 63% who said that they had done so. It is suggested that simultaneous assays of urinary nicotine and cotinine may be a useful means of verifying patients' current smoking habits.     

Ethnic variation in CYP2A6 and association of genetically slow nicotine metabolism and smoking in adult Caucasians

Genetically variable CYP2A6 is the primary enzyme that inactivates nicotine to cotinine. Our objective was to investigate allele frequencies among five ethnic groups and to investigate the relationship between genetically slow nicotine metabolic inactivation and smoking status, cigarette consumption, age of first smoking and duration of smoking. Chinese, Japanese, Canadian Native Indian, African-North American and Caucasian DNA samples were assessed for CYP2A6 allelic frequencies (CYP2A6*1B-*12,*1x2). Adult Caucasian non-smokers (n = 224) (1-99 cigarettes/lifetime) and smokers (n = 375) (> or = 100 cigarettes/lifetime) were assessed for demographics, tobacco/drug use history and DSM-IV dependence and genotyped for CYP2A6 alleles associated with decreased nicotine metabolism (CYP2A6*2, CYP2A6*4, CYP2A6*9, CYP2A6*12). CYP2A6 allele frequencies varied substantially among the ethnic groups. The proportion of Caucasian slow nicotine inactivators was significantly lower in current, DSM-IV dependent smokers compared to non-smokers [7.0% and 12.5%, respectively, P = 0.03, odds ratio (OR) = 0.52; 95% confidence interval (CI) 0.29-0.95]; non-dependent smokers showed similar results. Daily cigarette consumption (cigarettes/day) was significantly (P = 0.003) lower for slow (21.3; 95% CI 17.4-25.2) compared to normal inactivators (28.2; 95% CI 26.4-29.9); this was observed only in DSM-IV dependent smokers. Slow inactivators had a significantly (P = 0.03) lower age of first smoking compared to normal inactivators (13.0 years of age; 95% CI 12.1-14.0 versus 14.2; 95% CI 13.8-14.6), and a trend towards smoking for a shorter duration. This study demonstrates that slow nicotine inactivators are less likely to be adult smokers (dependent or non-dependent). Slow inactivators also smoked fewer cigarettes per day and had an earlier age of first smoking (only dependent smokers).     

Assessment of prenatal smoke exposure by determining nicotine and its metabolites in maternal and neonatal urine

Urine specimens were collected from 75 pregnant women before childbirth and from their newborns within 48 postnatal hours. A high-performance liquid chromatography (HPLC) method was used to determine urinary nicotine and its metabolites, cotinine and trans-3'-hydroxycotinine (OH-cotinine) to objectivise prenatal smoke exposure. Using the sum of nicotine metabolites as a marker, 34 women were classed as not exposed to smoke ( < 15 nmol/l), 18 as passive smokers (15-400 nmol/l), and 23 as active smokers ( > 400 nmol/1). The newborns of active smokers exhibited significantly (P < 0.001) higher nicotine metabolite concentrations than did those of either non-exposed women or passive smokers. A close correlation was found to exist between maternal and neonatal nicotine and cotinine concentrations (r=0.8968 and r=0.9205, respectively). For OH-cotinine, this correlation was particularly close when maternal, but not neonatal, OH - cotinine was adjusted to creatinine (r=0.9792). The neonatal/maternal urine concentration ratios for cotinine and OH-cotinine were noted to not significantly depend on the time of postpartal urine collection. Within the first two postnatal days, the extent of current prenatal smoke exposure attributable to active smoking of the mother was best reflected by the urinary concentrations of cotinine plus OH-cotinine without adjustment to creatinine.     

Hubble-bubble (water pipe) smoking: levels of nicotine and cotinine in plasma,saliva and urine

OBJECTIVES: The purpose of the present study was to assess the levels of nicotine and cotinine in biological fluids (plasma, saliva, and urine) following hubble-bubble (HB) smoking. METHODS: Fourteen healthy male volunteers, aged 28 +/- 8 years, body weight of 82.7 +/- 13.53 kg, participated in the study. All volunteers were habitual HB smokers for 3.29 +/- 1.90 years who smoked at least 3 runs per week with an average of 20 g Mua'sel per run. Volunteers were requested to avoid smoking, at least 84 hours prior to the time of the study. After baseline samples were taken, volunteers started smoking 20 g of Mua'sel for a period of 45 minutes. Heparinized blood samples (5 or 10 ml each) were drawn for nicotine and cotinine analysis before, during and after the smoking period. Saliva samples were collected just before smoking (time 0) and at the end of smoking (45 min). Urine also was collected at time 0 and 24-hour urine collection was also taken to measure nicotine and cotinine excretion. Nicotine and cotinine were extracted from samples and assayed by gas chromatography. All data are presented as mean +/- SEM throughout the text, Tables and Figures unless indicated otherwise. RESULTS: Plasma nicotine levels rose from 1.11 +/- 0.62 ng/ml at baseline to a maximum of 60.31 +/- 7.58 ng/ml (p < 0.001) at the end of smoking (45 min). Plasma cotinine levels increased from 0.79 +/- 0.79 ng/ml at baseline to its highest concentration of 51.95 +/- 13.58 ng/ml (p < 0.001) 3 hours following the end of smoking. Saliva nicotine levels significantly rose from 1.05 +/- 0.72 to 624.74 +/- 149.3 ng/ml and also saliva cotinine levels significantly increased from 0.79 +/- 0.79 ng/ml to 283.49 +/- 75.04 ng/ml. Mean amounts of nicotine and cotinine excreted in urine during the 24-hour urine collection following smoking were equal to 73.59 +/- 18.28 and 249 +/- 54.78 microg, respectively. CONCLUSION: Following a single run of HB smoking, plasma, saliva and urinary nicotine and cotinine concentration increased to high values. This observation suggests that HB may not be an innocent habit, as people believe.     

High dose transdermal nicotine therapy for heavy smokers: safety,tolerability and measurement of nicotine and cotinine levels

Transdermal nicotine has been shown to relieve nicotine withdrawal and to double smoking cessation rates compared to placebo in clinical trials. A 21 or 22 mg/day dose provides a steady state serum nicotine that is less than obtained from smoking. Limited information is available about higher nicotine patch doses. To define better the optimal dosing of nicotine patch therapy, we undertook an open-label study to determine the safety and tolerability of 44 mg/day dose for smoking cessation in subjects smoking 20 cigarettes per day. Forty smokers received 44 mg/day of transdermal nicotine for 4 weeks followed by 4 weeks of 22 mg/day. Of the 40 subjects enrolled, 38 (95%) completed the 4 weeks of 44 mg patch therapy and 36 (90%) completed the entire 8 weeks of patch therapy. Non-smokers at week 4 had a mean serum nicotine level of 23.4±11.7 ng/ml and cotinine of 152.2±87.3 ng/ml. Percent replacement was calculated by dividing the steady state level at week 4 by the baseline level while the subjects were smoking their usual number of cigarettes. Percent nicotine replacement for non-smokers at week 4 (while on 44 mg nicotine patch) averaged 158%±108.4, and for cotinine was 112.0±73.8. For nicotine, 33% of non-smokers at week 4 had 100% nicotine replacement and for cotinine 63% 100% replacement. Biochemically confirmed point prevalence smoking cessation rates were 65% and 55% at weeks 4 and 8 of patch therapy, respectively, and self-reported smoking cessation at 3 months was 50%. The most common effect was skin irritation at the patch site. A single subject was admitted for myocardial infarction following step-down from 44 to 22 mg of replacement nicotine. The subject was not smoking and the adverse event was deemed to be not related to the patch therapy. Sleep complaints were reported in 33% of subjects during the 44 mg phase. Other complaints were infrequent. We conclude that 44 mg per 24-h nicotine patch therapy in heavy smokers is safe, tolerable, and without significant adverse events.