Keywords
drug use, agriculture-related workers, Thailand
drug use, agriculture-related workers, Thailand
Illicit drug (ID) use has been widely recognized as a challenge to both individual health and society. According to the United Nations Office on Drugs and Crime, 5.6% of adults (15–64 years) across the globe used IDs at least once in 2016 and >10% of those drug users have suffered from drug-use disorders1. In the Association of Southeast Asian Nations (ASEAN), the rate of drug users in 2016 who accessed treatment systems was 27.8 per 100,000 people. Over 80% of treated people were methamphetamine users2. A 2016 household survey in Thailand revealed that 1.4 million Thai people aged between 12–65 years used drugs, 2.8% of the adult Thai population. The results from the last Thai national survey showed that cannabis, kratom (Mitragyna speciosa Korth), and methamphetamine were the three most commonly used drugs among ID users3. Government statistics reported that only 13% of these drug users were estimated to access all treatment systems in 20164. Although drug use in Thailand has been lower than the global average, the problem has been a part of the national agenda since 20015.
Since 1360, Thailand has been affected by the problem of illicit substance use6. Common indigenous plants from which IDs are sourced are opium, cannabis, and kratom. The first synthetic drug used in the population was heroin, first noticed in the early 1960s. The use of stimulants (amphetamine and methamphetamine) evolved into a major epidemic in the early 1970s. Volatile substances (benzene, lacquer, and glue) appeared in the late 1970s7. In the late 1990s, a new set of substances, including ecstasy, ketamine, crystalline methamphetamine, and cocaine, began to be widely used8. Recently, the use of non-medical pharmaceutical drugs and new psychoactive substances has become evident9. However, official statistics show that methamphetamine users were the biggest group of drug users who accessed treatment10. Since cannabis and kratom are less harmful than other drugs, only a few users have required treatment.
In general, people take drugs for a variety of reasons. Psychostimulants are thought to reduce fatigue and enhance activities11,12. Methamphetamine, which is an amphetamine-type stimulant (ATS), has a long history of use in the Asia-Pacific region13. Presently, among ASEAN member states, methamphetamine is distributed in crystal, powder, and pill forms14.
In Thailand, ATSs have been known since the early 1960s and are thought to have been a major problem since the 1990s15. Recent statistics show that three quarters of ATS users are methamphetamine users10. Additionally, two-thirds of drug users who sought treatment from the government system were laborers, including agriculture-related workers. Agricultural products accounted for 8.7% of Thailand’s annual GDP16. Of all workers employed in 2016, 30% were agriculture-related workers17. Recent studies have reported significant associations between substance use and agricultural activities18,19.
Studies have found that substance abuse behavior was affected by various social determinants, including personal characteristics and relationships with peers/family and the neighborhood20–22. Some studies have focused on individual and interpersonal factors related to substance abuse21,23. Other studies have explored the extent of neighborhood factors that influence the risk of relapse21,24–26. A few studies in Thailand have reported how social factors (a combination of individual, peer, and family factors) influenced substance use27,28.
Although evidence has emerged showing that agriculture-related workers potentially use drugs, the prevalence of drug abuse and neighborhood cluster association was unclear. There were two objectives in this study: to explore the proportion of drug users among agriculture-related workers and to investigate the association between cluster-level factors and substance use among agriculture-related workers by using model simulation following the method described by Bronfenbrenner29.
This cross-sectional study was conducted from September 2017 to July 2018.
In 2017, a total of 5,911,567 individuals had registered as agricultural-related workers in Thailand30. Only workers who had worked for the past 3 months were eligible to participate in the survey. The prevalence of substances used from the latest national household survey in 2016 was used as a study parameter to calculate sample sizes3. The sample size calculation method for prevalence survey31 was employed with adjustment of design effect from multistage sampling. With an expected 10% non-response and ±1%% error, a sample size of 3140 individuals was targeted. Stratified multistage cluster sampling was employed. Thailand was stratified into 10 geographical zones on the basis of governmental narcotic operation areas; each zone comprised 7–12 provinces. Each zone was a systematically sampled province (one zone per province). The 10 sample provinces were Chiangmai, Phitsanulok, Khon Kaen, Nakornrachasima, Samitprakarn, Chonburi, Samutsakorn, Krabi, Satun, and Bangkok. Then, the agricultural clusters of each province were mapped. Only one cluster was randomly selected from each province, which gave 10 clusters altogether. Households were systematically selected from the updated map of individual clusters. The number of households was determined on the basis of the probability proportional to size. Simple random sampling using a table was employed to obtain a sample from each household (one household per sample). Of 3140 intended samples, 2936 (93.5%) individuals agreed to participate in the survey (ages ranging from 16 to 69 years old, with an average of 36.6 years old; 61.3% (1799) were males).
After the baseline survey, 124 current methamphetamine users agreed to participate in structured observation regarding their drug use (age ranging from 18 to 58 years old, with an average of 27.4 years old; 88.7% (110) were males).
Outcomes of the study were identified as drug use prevalence. In this study, drug use was defined as the use of illicit drugs (IDs) (heroin, cannabis, methamphetamine, etc.); legal substances, such as non-prescription drugs alcohol, tobacco and caffeine, were not included. Of all IDs, methamphetamine is hypothesized to be widely used among agricultural rated workers to accelerate productivities resulting in higher prevalence. Annual prevalence as well as past month prevalence was obtained.
The interview questionnaire and structured observation guideline were developed by 12 experts32. The interview questionnaire comprised individual-level, interpersonal-level, and cluster-level variable sections, as well as substance use. The structured observation guideline emphasized pattern of methamphetamine use and its effects.
A total of 20 research assistants (two for each province, one male, one female) were trained to conduct field work (updating a cluster map, devising a household sampling frame, randomly selected samples, requesting consent, and interviewing the samples). The research assistants asked the intended participants to provide written informed consent, waited a couple of days to allow the participants to make their own decision, and, then, made an appointment for them to come back to be interviewed/observed. Data from the survey were gathered from September to November 2017 via private, face-to-face interviews. Interview guides are available as Extended data. The participants chose a convenient place and time for their interviews (e.g., the participant’s household). An average of 1–1.5 hours was spent for each interview. After the interview, the research assistants requested written consent to participate in structured observation of the drug users. Only those who consented (n=124) were observed regarding their drug-use behavior—such as when and how IDs were used, and the amount and frequency used—and its effects. The research team conducted participant observations from November 2017 to July 2018 (3–5 times for each sample, 1–2 days for each observation).
The outcome variable was substance use. The current use in this study was defined as having taken drugs at least once in the past month from the interview date.
The individual-level variables included sex, age, education, monthly income, and marital status. All variables were categorized as dichotomous variables.
The interpersonal-level variables were assessed to reflect the extent to which the drug user’s peers used methamphetamine or other IDs. Potential covariates were accounted for by adjusting for individual and interpersonal-level variables. These variables were selected on the basis of evidence regarding factors that affect substance abuse and the neighborhood environment20,21,23,25,28.
The one cluster-level variable was the level of drug use in each of the provinces sampled in 2017. The level of drug use was defined as the proportion of the population that used drugs and was partly assessed by the number of drug users who accessed the treatment system. In this study, the treatment rate was the proportion of registered clients of governmental treatment centers in the population in a given area. The estimated rate (per 1000 people) of ID users/methamphetamine users was determined from the survey in a given area in 2017.
Data double-entry was employed. SPSS for windows version 16.0 was used. Descriptive statistics were used to analyze all socioecological factors. Multilevel binary logistic regression analysis via generalized linear mixed models was used to analyze the associations among cluster-level variables, each covariate, and substance use. Level 2 comprised individuals at level 1 (individual-level variables and interpersonal-level variables) nested within clusters at level 2 (consisting of two variables). The model building process started with a null model consisting of no predictors, and a series of two-level models was developed. Model 1 fit only individual-level variables into the model. Then, in model 2, all interpersonal-level variables were entered into model 1. Finally, in model 3, all cluster-level variables were entered into model 2. The median odds ratio (mOR) and interval odds ratio (IOR) were applied to measure the variation of substance use in different clusters and the effects of cluster-level variables, respectively. The level of statistical significance was set to p-values < 0.05.
This research project was approved by the Human Research Ethics Committee of Khon Kaen University and was conducted in accordance with the principles of the Declaration of Helsinki and International Conference on Harmonization Good Clinical Practice standards. Written informed consent was obtained from the participants and from the parents/guardians of minors.
The median age of the agriculture-related workers was 36 years; 15.9% of the workers were <25 years old and 47.7% had obtained elementary education and lower (Table 1). One-third of the workers were poor (earned < per annum), 29.4% were current smokers and 19.1% were habitual smokers (>20 days in the past month), and 17.9% had smoked >1 pack daily. Regarding alcohol, 48.7% were current alcohol drinkers, 30.4% were habitual drinkers, and 24.1% had drunk >330 mL of beer or the equivalent amount of alcohol every time they drank (which resulted in a blood alcohol level >50 mg/dL). Regarding substance abuse, 57.7% (n=1695) of the participants currently used non-medical pharmaceutical drugs, mostly analgesics, codeine mixture cough syrup, sedatives, or opioids. Among the agriculture-related workers, 73.5% (2158) had used IDs at some point in their life, and 13.9% (408) were current ID users. This number is much higher than 1.99 in general population (Kanato et al. 2017). Current ID users were mostly regular and contracted workers also. There are a few reported histories of drug treatment for these categories of workers in the government system. All information gathered during this study is available as Underlying data32.
Values are presented as number (%) or mean ± standard deviation.
Among 408 illicit drug current users, 350 currently used methamphetamine. The rest used kratom, cannabis, inhalants, opiates/opioid, ecstasy, ketamine, and cocaine.
Users used methamphetamine 1–3 times daily (1–6 pills each time), around 30 minutes before work for first intake and every 5–6 hours booster. Mostly, users smoked methamphetamine (put 1 pill on foil then used lighter to burn and applied straw to take it). A few put 1–2 pills into drinking water. They recognized the effect of the drug (energetic, painless etc.) 1–2 minutes after smoking, or around 10 minutes after drinking. There are few reports of drug treatment for these categories of workers in the government system.
Concerning both the ID use (Table 2) and methamphetamine use (Table 3), the treatment rate showed a statistically significant association with decreased substance use. Regarding ID estimation, only ID use (Table 2) was significantly associated with increased substance use; however, the effect was extremely small.
Variable | Bivariate OR (95%CI) | Model 1 aOR (95%CI) | Model 2 aOR (95%CI) | Model 3 aOR (95%CI) |
---|---|---|---|---|
Sex, male (ref: female) | 0.87 (0.70, 1.08) | 5.36 (2.23, 12.89)*** | 5.37 (2.29, 12.60)*** | 5.40 (2.36, 12.37)*** |
Age >25 years (ref: <25 year) | 1.07 (0.81, 1.41) | 1.73 (1.19, 2.54)** | 1.73 (1.19, 2.51)** | 1.74 (1.20, 2.53)** |
Monthly Income <US$300 (ref: >US$301) | 2.45 (1.87, 3.21)*** | 0.94 (0.70, 1.26) | 0.94 (0.73, 1.20) | 0.94 (0.74, 1.20) |
Education, primary (ref: secondary and above) | 1.05 (0.85, 1.30) | 0.96 (0.73, 1.26) | 0.96 (0.73, 1.26) | 0.95 (0.72, 1.26) |
Marital status, single (ref: married) | 1.37 (1.10, 1.69)* | 1.40 (0.93, 2.10) | 1.39 (0.95, 2.03) | 1.39 (0.95, 2.03) |
Non-prescription (ref: no) | 10.05 (7.02, 14.40)*** | 4.30 (2.03, 9.11)*** | 4.32 (1.95, 9.54)*** | 4.32 (1.96, 9.50)*** |
Interpersonal level | ||||
Peer ID users | 1.004 (0.998, 1.009) | 0.999 (0.981, 1.017) | 0.999 (0.981, 1.017) | |
Level 2 | ||||
Cluster level | ||||
Treatment rate | 0.034 (0.025, 0.045)*** | 12.74 (1.85, 87.97)* | ||
ID estimation | 1.007 (1.002, 1.012)* | 0.993 (0.984, 1.001) | ||
Random effects | ||||
Level 11 | 1 | 1 | 1 | |
Level 22 | 4.24 (2.11)* | 4.23 (2.10)* | 2.31 (1.37) | |
Median OR (mOR) | 7.13 | 7.11 | 4.26 | |
IOR-80% for treatment | 0.8108, 200.275 | |||
IOR-80% for estimation | 0.063, 15.606 |
The respondents who were single, had low incomes, and currently used non-medical pharmaceutical drugs were more likely to use IDs and methamphetamine (Table 2 and Table 3).
Variable | Bivariate, OR (95%CI) | Model 1, aOR (95%CI) | Model 2, aOR (95%CI) | Model 3, aOR (95%CI) |
---|---|---|---|---|
Sex, male (ref: female) | 0.71 (0.57, 0.89)** | 5.26 (1.87, 14.77)** | 5.28 (1.87, 14.93)** | 5.34 (1.96, 14.50)** |
Age >25 years) (ref: <25 years | 1.06 (0.78, 1.43) | 1.96 (1.13, 3.42)* | 1.96 (1.13, 3.40)* | 1.98 (1.14, 3.49)* |
Monthly income <10,000 (ref: >10,000) | 3.41 (2.47, 4.71)*** | 1.10 (0.72, 1.68) | 1.11 (0.72, 1.69) | 1.10 (0.73, 1.67) |
Education, primary (ref: secondary and above) | 1.19 (0.95, 1.48) | 1.11 (0.83, 1.49) | 1.11 (0.83, 1.49) | 1.11 (0.83, 1.50) |
Marital status single (ref: married) | 1.27 (1.01, 1.60)* | 1.20 (0.67, 2.14) | 1.20 (0.67, 2.14) | 1.20 (0.67, 2.14) |
Non-prescription (ref: no) | 12.66 (8.24, 19.46)*** | 4.33 (1.64, 11.40)** | 4.33 (1.64, 11.39)** | 4.33 (1.65, 11.34)** |
Interpersonal level | ||||
Meth Network | 1.001 (0.986, 1.016) | 1.003 (0.996, 1.009) | 1.003 (0.997, 1.009) | |
Level 2 | ||||
Cluster level | ||||
Treatment rate | 0.01 (0.01, 0.02)*** | 15.34 (1.24, 190.32)* | ||
Meth users estimation | 0.99 (0.97, 1.01) | 0.99 (0.80, 1.24) | ||
Random effects | ||||
Level 11 | 1 | 1 | 1 | |
Level 22 | 4.98 (2.49)* | 4.98 (2.49)* | 3.05 (1.85) | |
Median OR (mOR) | 8.4 | 8.4 | 5.29 | |
IOR-80% for treatment | 0.647, 363.333 | |||
IOR-80% for estimation | 0.0421, 23.673 |
The mOR in all models was >1, which indicated that the between-cluster variation in substance use was greater than the within cluster-level variation; all of the IOR-80% intervals contained 1, which confirmed this finding further (Table 2 and Table 3).
Table 2 presents the results of the multilevel binary logistic regression models for ID use. In model 1, the analysis of the association of the individual-level variables with substance use showed that a higher likelihood of ID use was associated with males, older age, and non-prescription drug use. In model 2, drug use among peers was not associated. In the final model (model 3), 2 cluster-level variables (i.e., treatment rate and ID estimation variables) were added to the model, and each 1-unit score increase in treatment rate was associated with a significant 12-fold increase in the likelihood of ID use.
We hypothesized that methamphetamines were used to accelerate the productivity of agriculture-related workers. A series of similar models was used to estimate the odds ratio of methamphetamine use, as shown in Table 3. In models 1 and 2 of this category, older respondents were more likely to use methamphetamines than were younger respondents. Males and non-prescription drug use were significantly associated with an increase in the likelihood of methamphetamine use. Finally, in model 3, the results showed similar associations between individual and interpersonal-level variables with substance use, as in model 2. In the final model (model 3), 2 cluster-level variables, i.e., treatment rate and ID estimation variables, were again added to the model, and each 1-unit increase in treatment rate was associated with a significant 15-fold increase in the likelihood of methamphetamine use.
With the objective of exploring the prevalence of drug use among agriculture-related workers, this study found that the past month’s prevalence was much higher than the prevalence in the general Thai population, particularly for use of methamphetamine3,9. This difference in prevalence indicated that agriculture-related workers use stimulant drugs to increase their productivity, which may give them more income. Recent investigations have shown that use of IDs has spread to regular and contracted workers, indicating that IDs have become more easily accessible and affordable. Thus, functional use of drugs is acceptable by workers.
The results showed that neighborhood problems, such as health problems (treatment accessibility rate), were associated with ID use, particularly methamphetamine, consistent with other research findings22,33,34. A possible explanation for this finding is neighborhoods/clusters with a high prevalence of drug use reflect drug availability and accessibility, which could be enabling factors for workers throughout the community. Methamphetamine is an ID popularly used by drug users in Thailand. Covariates, such as sex, age, and non-prescription drug use, were related to both ID use and methamphetamine use. This finding is consistent with other research findings20,35–37.
This study used data from a cross-sectional survey; therefore, it cannot establish a temporal relationship or causality. However, the study strengths are the use of treatment rate as a cluster-level factor (enables an objective assessment), providing more reliability than that of previous subjective assessments38,39. Another study strength is it controlled for a wide range of covariates and used a large sample size and a nationally representative sample, meaning that the findings can be generally applied to the larger Thai population. Not only did this study provide further insights into cluster-level affects on substance use, but also describes associated factors adjusted for cluster environment among agricultural at national scale. However, prospective studies to further investigate may be required.
This study was successful in collecting data with a high response rate. The findings of the present study can also be applied to other similar contexts. The authors suggest further qualitative study on the beliefs of among agricultural regarding drug use for working. However, patterns of drug use may be better measured using open-ended questions, where among agricultural are asked to provide information freely without being influenced.
This study demonstrated association of personal characteristics of agricultural related workers and substance use particularly methamphetamine. In addition, cluster-level factors (treatment rate and ID estimation) were also significantly associated. Thus, the development of prevention measure on substance use should be taking into account the area based socioeconomic environment to pursue the more effective demand reduction.
Open Science Framework: Drug use among agriculture-related workers in Thailand.
https://doi.org/10.17605/OSF.IO/DWV9G32.
This project contains the following underlying data:
Open Science Framework: Drug use among agriculture-related workers in Thailand. https://doi.org/10.17605/OSF.IO/DWV9G32.
This project contains the following extended data:
Data are available under the terms of the Creative Commons Attribution CC 1.0 International license (CC0 1.0 Universal).
N.J. and M.K. conceived the ideas; N.J. and P.L. collected the data; N.J., M.K. and P.L. analyzed the data; and M.K. led the writing.
This study was funded by the Office of the Narcotics Control Board (grant no. ONCB18/FY2560).
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
The authors would like to thank the ISAN Academic Network, Khon Kaen University, for their generous support. The authors would also like to thank the Office of the Narcotics Control Board for funding this study.
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Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Medical/cultural/social anthropology; public health; immigration; alcohol/drug use among populations that experience health disparities.
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