Introduction

A psychoactive drug, psycho-pharmaceutical, or psychotropic drug is a chemical substance that changes brain function and results in alterations in perception, mood, consciousness, cognition, or behavior [1]. Based on their common effects, psychoactive substances can be classified as stimulants (nicotine present in tobacco, caffeine contained in coffee, cocaine, amphetamine, khat, etc.), depressants (alcohol, barbiturates, benzodiazepines, chloral hydrate, rohypnol, etc.), narcotics (heroin, morphine, codeine etc), hallucinogens (alpha-methyltryptamine, ketamine, phencyclidine, D-lysergic acid diethylamide etc), and cannabis (marijauna, hashish, hash oil etc) [2]. Psychoactive drugs that are used for recreational purposes include alcohol, tobacco, caffeine, cocaine, Lysergic Acid Diethylamide (LSD), and cannabis [3]. Psychoactive drugs are used not only to enhance pleasure but also to achieve social, religious, and ritualistic goals [4]. However, caffeine, tobacco, and alcohol are legally available while the rest are not legally available [3].

It is estimated that 1 in 20 adults, or a quarter of a billion people between the ages of 15 and 64 years, used at least one drug in 2014 according to 2016 world drug report [5]. Globally, over 29 million people suffer from drug use disorders, and of those, 12 million are people who inject drugs (PWID) of whom 14.0% are living with HIV [6]. The impact of drug use in terms of its health consequences continues to be devastating. The global disease burden attributed to alcohol and illicit drugs is estimated at 5.4% while 3.7% is attributed to tobacco use alone [6].

Makanjuola et al., [7] pointed out that the use of psychoactive substances, especially alcohol, was really common among long distance vehicle drivers in Nigeria. However, Abiona et al. [8] revealed that all the respondents (commercial vehicle drivers) engaged in the use of commonly available alcoholic beverages in various motor parks. The sale of marijuana, cannabis and the likes go along side with the alcoholic beverages in various motor parks in Ogun State.

Substance use is very common among Nigerians which of course include the public vehicle drivers across the country. According to Iwerimie-Jaja [9] Nigerians are a substance/drug-using society. He further affirms that in the market are consciousness-altering substance such as marijuana, heroin and cocaine. The public safety in the excessive use of these drugs is that it can influence their users to commit crime and delinquency [9]. Moreover, it is a common thing to find people selling several kinds of substance ranging from alcohol, India hemp and the likes in public places particularly at motor parks across the country. This has created avenues for the commercial vehicle drivers and their assistants to patronize substance vendors at the parks and feel high at any time. With this observation, substance abuse is a common phenomenon among the commercial vehicle drivers in Nigeria especially Lagos State. Oluwadiya et al., [10] stated that “paraga”, an alcoholic herbal preparation that comes in different varieties had been shown to be commonly available to commercial vehicle drivers in southern Nigeria.

Studies from different fields have shown a long-standing interest in studies related to the consumption of alcohol and tobacco for two reasons. First, because of the social and health related challenges’ associated with the abusive consumption of these two commodities, and secondly, because of the need to evaluate the impact of different tax schemes on these goods in promoting government revenues, improving general welfare and controlling consumption [4]. For instance, the Spanish government in September 2005 increased the tax rates on tobacco and alcoholic beverages once more, and is expecting increased revenues and reduction in consumption of these products. From this perspective, it is no wonder that the consumption of alcohol and tobacco are often considered as two related matters by policy-makers, health officials and social scientists.

Cigarette and alcohol policies in Nigeria face a dilemma. A large number of studies have shown that cigarette consumption and excessive alcohol consumption are very harmful to health [11]. Globally, tobacco use and the harmful consumption of alcohol have been identified as two important shared risk factors for 80% of diseases [11-12]. According to World Health Organization, [12], tobacco use is the second leading cause of death while the harmful use of alcohol is the third leading cause of morbidity. In many cases, there is a synergy between tobacco and alcohol use. Studies in high income countries have found that people who smoke are much more likely to drink, and vice versa [13]. Dependence on alcohol and tobacco may also be correlated; people who were dependent on alcohol were three times more likely than those in the general population to be smokers, and people who were dependent on tobacco were four times more likely than the general population to be dependent on alcohol [14].

The use of these psychoactive substances by vehicle drivers is a common occurrence globally [15-17]. This practice involves the use of virtually all substances known today. Concerns are growing over the incidence of road traffic accidents in drivers who drive under the influence of these substances, especially alcohol and cigarette as reported by WHO [18]. Although road crashes may have multiple interacting causal factors, some accident culpability and responsibility analysis had demonstrated that serum levels of substances use correlates positively with road traffic accidents [19]. Substance use could be a regular activity in a driver who then takes the substance while driving as is observed in day-to-day vehicle drivers [20-21] or it could be a routine behavior related to the occupation of driving [16]. Studies [22-26] have shown the use of substances by drivers and its association with road traffic accidents.

Prevalence of cigarette smoking and alcohol consumption among RTWs in Nigeria continues to increase despite the role that government is playing in controlling the consumption. Motor vehicle accident (MVA) is a significant cause of mortality and morbidity in Nigeria, and driving under the influence of alcohol and cigarette have been implicated in the occurrence of MVAs [27]. In Nigeria, majority of the RTW are self-employed and owners of the vehicles they drive, while some drivers make daily or weekly monetary delivery to the owners of the vehicle they drive and some are conductors. They face the highway on top speeds on a daily basis, sometimes making more than one trip on their usual route. In order to reduce or minimize this stress, some of the drivers believe that, the use of substances such as alcohol, cigarette, kola nut, marijuana, and other central nervous system (CNS) agents such as amphetamines will significantly improve their performance and keep sleep at bay for as long as possible [28]. Some even use heavy episodic drinking as means of constructing social identity. These substances are also frequently taken for social reasons. Ability of these substances to affect the Central Nervous System (CNS) will impair driving performance, and a high possibility of contributing to the occurrence of motor vehicle accidents (MVAs).

Because of the high morbidity and mortality associated with regular cigarette and alcohol consumption and with involuntary exposures to environmental tobacco smoke, smoking represents a significant health risk to both smokers and nonsmokers and places a significant economic burden on modern health care systems and on society as a whole [16]. Providing support to quit smoking is one of the areas of intervention in the fight against tobacco established by the World Health Organization Framework Convention on Tobacco Control [19]. Raising cigarette and alcohol taxes is an important policy tool to reduce cigarette and alcohol use, as recommended in the WHO MPOWER strategy for tobacco control.

There is very strong evidence that higher tobacco taxes and prices lead to significant reductions in tobacco use. These reductions are larger in low- and middle-income countries than in high income countries Framework Convention of Tobacco Control [29]. It is estimated that a tripling of excise tax on tobacco in most low- and middle-income countries would double cigarette prices, reducing consumption by about 40% [30]. In China, home to one third of the global population of smokers and where smoking kills 1 million people a year – it has been estimated that raising tobacco taxes so that they account for 75% of retail cigarette prices (up from 40% of the share of price in 2010) would avert nearly 3.5 million deaths from cigarette smoking [31]. Total taxes on cigarettes rose from 32% to 52% of retail price between 1993 and 2009 in South Africa. This contributed to a halving of tobacco consumption from about four cigarettes per adult per day to two cigarettes per day over a decade [32] and a nine-fold increase in government tobacco tax revenues [31].

Higher taxes imply increases in the sale price of cigarette and alcohol, which in turn reduces the demand for the goods, following the well-established economic relationship between price and demand for consumer goods. Price increases contribute significantly towards reducing consumption, increasing the number of attempts to quit, promoting cessation, and preventing initiation [33-34].

The Nigerian government is trying to adopt policies of Taxes (tariffs) recommended as a tool to reduce alcohol and cigarette consumption. It is widely often recommended that taxes are tools used to reduce alcohol and cigarette consumption. Tauchmann et al., [35], posited that a reduction in tobacco consumption results in a moderate reduction in alcohol consumption. Theoretically, this implies that alcohol and tobacco are complements. Hence, increase in the price of either alcohol or cigarette will therefore reduce the consumption of both. In fact, there is strong empirical evidence that smoking and drinking are not independent activities [36-39]. Therefore, taxing one will reduce the consumption of both and thus, achieve a double public health dividend. However, if they are substitutes, taxing one will induce consumers to increase consumption of the other, offsetting the public health benefits of the tax.

The Nigerian government has approved an amendment to the excise duty rates for alcoholic beverages and tobacco with effect from June 4, 2018 and the new e6cise duty rates were spread over a three-year period from 2018 to 2020 in order to moderate the impact on prices of the products. The Federal government stated that the upward review of the excise duty rates for alcoholic beverages and tobacco was to achieve a dual benefit of raising the government’s fiscal revenues and reducing the health hazards associated with tobacco-related diseases and alcohol abuse.

The contingent valuation method was developed as a method of eliciting WTP. This method was originally used for measuring the benefits of pure public goods and services without markets. In these circumstances, the WTP methodology was used to identify the monetary value that individuals attributed to certain goods and services to approximate the level of demand for those services. Initially used by environmental economists to value public goods and thus to define property rights, this technique has more recently been adopted by health economists to conduct prospective evaluations of health interventions and medical technologies. Interestingly, very few studies on cigarette smoking and alcohol cessation have used the WTP methodology in their estimations.

Ross [40] demonstrated the feasibility of using this technique to value a hypothetical studied of the impact of cigarette prices on young smokers’ behaviour by presenting hypothetical price increases ranging from US$0.50 to US$4.00 per pack. The expected behavioural response was stronger with higher increase. More recently, Ross et al., [41] observed consistent results among adult smokers in the ITC Four Country Survey data. Smokers were asked how they would respond to a 50% increase in cigarette price. The percentage of smokers who would try to quit ranged from 58% in the UK to 73% in Canada. Guillaumier et al., [42] also obtained the price to quit among Australian socioeconomically disadvantaged smokers, finding that half of smokers would try to quit at a 20% increase in price. Among those who would not try to quit at such increase of price, the median of the price needed to quit was about 150% of the usual price. It is usually desirable to combine diverse policies to reduce smoking prevalence, in addition to raising tax.

Smokers may respond to cigarette price increases in a number of ways. Firstly, they may quit smoking, which is the primary aim of the strategy. This response is evident in reduced prevalence rates [43-44], as well as in increases in quit attempts, quit intentions and motivation to quit following price increases (45, 40]. Increases in tobacco excise taxes that increase product prices can effectively demonstrate a reduction in overall tobacco consumption and prevalence of use by promoting cessation, preventing initiation and lowering consumption [43]. Findings from the International Tobacco Control Four-Country Survey (ITC-4) suggest that smokers living in areas with higher cigarette prices and taxes are significantly more motivated to quit [40] and are also more likely to report quit intentions in response to hypothetical price increases [46].

Non-tax policies are expected to enhance the effects of tax increase, based on an assumption that smokers exposed to non-tax policies would be motivated to quit at a lower price level. However, to our knowledge, no previous studies in Nigeria have comprehensively evaluated predictors of the willingness to quit smoking and drinking among RTWs in the Nigeria. Identifying these factors in specific cultural and socioeconomic settings is vital to developing appropriate intervention programs. Studies conducted in different countries have reported age, marital status, income, addiction level, past attempts to quit, social pressure, number of smoker friends, smoking status of family members, and antismoking media messages as significant predictors of the willingness to quit cigarette smoking and alcohol drinking.

Because the prevalence of smoking and drinking in Nigeria are seen more among transport workers either motor pack worker or commercial motorcyclists (Okada riders) and there is an exponential rise in smoking and drinking behaviour, the objective of this study was to estimate the Willingness to Quit (WTQ) Psychoactive substances use especially cigarette and alcohol using hypothetical 25% cigarette pack and alcohol bottle price rises. Specifically, the study attempted to (i) assess self-reported reactions to hypothetical price rises, as measured by Contingent Valuation Method (CVM), intention to quit and intention to make no changes to smoking/drinking behaviour and (ii) identify socioeconomic and smoking/drinking behavior characteristics among smokers/drinkers in response to hypothetical price rises. Generally, the WTQ was aimed at obtaining what increase in cigarette price per pack and price increase in per bottle of alcohol that would make RTWs try to quit (‘price to quit’). Furthermore, attempts were made to identify non-tax policies and socioeconomic factors affecting WTQ.

Methods

This study was conducted in Abeokuta the largest and capital city of Ogun state in southwest Nigeria. As of 2006, Abeokuta and the surrounding area had a population of 449,088. It is located between latitude 7^o9’39”N and 7.16083^oN and Longitude 3^o20’54”E and 3.34833OE. The respondents for the present study were the commercial intercity vehicle drivers in the five major motor parks in the city namely Kuto, Lafenwa, Ijaye, Asero and Panseke. Permission was obtained from the transport unions (National Union of Road Transport Workers (NURTW) and Road Transport Employers Association of Nigeria (RTEAN) of each of the selected motor park. Multistage sampling technique was used for this study. The first stage involves random selection of five (5) major motor parks in the study area. Second stage involved random selection of sixty (60) RTWs in each of the selected motor parks targeting a total of 300 RTW. However, out of a total of 300 drivers, 232 consenting drivers participated in the study. Informed consent was also obtained from each of the transport workers. Structured interview guide was administered at the motor parks to obtain information about socioeconomic characteristics as well as alcohol consumption and cigarette smoking.

WTQ (smoking and drinking cessation) were defined by answering “Yes” to the question: “Have you ever tried to quit smoking or drinking? The number of smoked cigarettes per week and the purchased cigarette price per pack of 20 cigarettes was self-reported. Also, the number of bottle of consumed alcohol per week and the purchased alcohol price per bottle was self-reported. These were to ascertained cigarette and alcohol consumption.

A payment scale format was used for this study, and respondents were shown a list of prefixed and ordered values from which they were asked to choose their answers. Using this format, the WTQ was explored in an innovative way: as the questionnaire progressed, the questions were gradually preceded by additional information about the potential benefits of the WTQ with a view to reducing the MVAs and risk acquiring a drinking/smoking-related and to assess incrementally whether a respondent’s WTQ value would change with the introduction of additional information. This was applied only to those who had expressed a willingness to quit.

To elicit consumers’ WTQ the study applied contingent valuation method (CVM), which helps to find out how much an individual would be willing to pay by using hypothetical survey questions. Double bounded dichotomous choice contingent valuation method (DBDC-CVM) was used for this study because it has more efficiency as well as more information than single bounded approach [47].

In this study, designing hypothetical prices (bid amoint) to apply double bound dichotomous bid was based on the questionnaire pretest and the prices of cigarette and alcohol in the markets (N 350($0.96)/bottle and N250($0.68)/packs for alcohol and cigarette respectively). Bidding system was used in Table 1. Each RTW was asked for answering one of four random bids set below to minimize the bias of starting bids.

Using double bounded approach, respondents were asked two questions. Two questions were used from the survey: “How much of a cigarette price increase would it take to make you try to quit smoking or drinking?” “Would that be an increase in the cost per pack or per single cigarette and per bottle?” The study included the following clarification to avoid respondents’ confusion: “the study does not want to know how much the difference in price would be, not how much the higher price would be.” Question format was “Are you willing to quit consumption of alcohol and cigarette in public places during your work hours. Each question has two choices: yes or no. If saying “yes” in the first question, higher amount of bid will be given in the second question; otherwise, lower amount with saying “no”. Therefore, one of four abilities of a respondent can be: 1. Yes–Yes (YY), 2. Yes–No (YN), 3. No–Yes (NY), 4. No–No (NN).

In order to elicit WTQ, standard double bounded model Hanemann et al., [47] was used. Therefore, WTQ is generally expressed by function:

[endif]-->

Where:

α = intercept of the model

[endif]--> = proposed price (hypothetical price) given to respondents

Β = the coefficient of Bid

[endif]-->= the vector of socioeconomic variables of consumer ith and the non-tax policy variables

[endif]--> = the coefficients of Zi

i = individual consumer (ith)

j = kind of substances abuse (cigarette/ alcohol)

Results

Socio-economic Characteristics, Pattern of Alcohol and Cigarette consumption among Respondents.

Result of the socioeconomic characteristics (Table 1) show that all the respondents were male and aged between 25 and 45 years with mean age of 38years. Most of them were married (85.34%) and had primary education or less (74.1%). However, 59.48% had been engaged in road transport work for 5 – 10 years. Table 2 shows that majority (72.4%) of the respondents currently consumed both alcohol and cigarette with 24.14% and 53.5% of these having their first initiation at less than 18 years. Eleven to twelve bottle of alcohol was consumed by 66.38% of the respondent and 1 to 40 sticks of cigarette was consumed by 53.45% of the respondent in the 7 days memory recall. Smoking stage was defined using Lloyd-Richardson [48] definition. It classified smoking stage on the basis of smoking frequency and present smoking status; Never smokers (2.6%) were defined as those adolescents who denied ever trying a puff or two of cigarettes; experimental smokers (18.1%) were defined as those who endorsed trying cigarettes, although denied smoking within the past week or ever smoking regularly i.e. intermittent smokers (23.3%) were defined as those who reported smoking between 1 and 10 sticks per week; addictive smokers (53.0%) were defined as those who reported smoking on a daily basis within the past week. The most common patterns of alcohol use in this study are binge drinker (76.7%) and social drinker (23.3%). Binge drinking is a pattern of alcohol use where people episodically drink excessively. Social drinkers are those who only drink occasionally and rarely go above the recommended levels. Weeks may go by without them even thinking about alcohol if they are advised to stop for health reasons they will have no problem doing so.

Willingness to Quit Psychoactive Substance Use

Table 4 indicates that about 43% of the respondents are willing to quit for the increase in price, while 48% were willing to quit cigarette consumption if 25% increment in prices were imposed. Findings from the International Tobacco Control Four-Country Survey (ITC-4) suggested that smokers living in areas with higher cigarette prices and taxes are significantly more motivated to quit and are also more likely to report quit intentions in response to hypothetical price increases [46]. Kim and Lee [49] stated that in the cohort study of 700 Korean male adults conducted from 2004 to 2005, 11.0% of smokers stopped smoking and 22.2% of smokers reduced smoking in 6 months after the price increase. However, Kim [50] found that price increase influenced the decision of 26.5% adolescent to quit and 38.2% willing to reduce smoking. The respondents were later asked to respond to the double-bounded dichotomous choice questions with two bid prices: a starting bid and a follow-up bid.

Distribution of the Double-Bounded Willingness to Quit Psychoactive Substance Use Responses

Table 5 presents the distribution of the double-bounded WTQ responses for each of the substance. In terms of the different structure of bid prices, the proportions of respondents were distributed equally to the bid structure of versions A, B, C and D respectively. The bid designs in table 4 captured the WTQ ranges quite well. The proportion of the respondents who wereWTQ

Table 1: Respondents’ Socio-economic Characteristics,