New Nigerian Journal of Clinical Research

: 2019  |  Volume : 8  |  Issue : 14  |  Page : 97--103

Willingness to pay for antipsychotic medications in two tertiary health institutions in Nigeria

Wednesday Joshua Edefo1, Stella F Usifoh2, Waka Anthony Udezi2,  
1 Department of Pharmacy, Federal Neuro-Psychiatric Hospital, Benin City, Nigeria
2 Department of Clinical Pharmacy and Pharmacy Practice, University of Benin, Benin City, Nigeria

Correspondence Address:
Dr. Wednesday Joshua Edefo
Department of Pharmacy, Federal Neuro-Psychiatric Hospital, PMB 1108, Benin City


Objectives: Antipsychotic medications availability and affordability enhance patients' compliance and consequently improving their productivity. In Nigeria, where about half the number of her population is impoverished, and health-care cost burden is mostly out of pocket of patients. The study objectives are to determine patients' preference in three antipsychotic medications with different attributes and side/adverse effects and a hypothetical antipsychotics medication with highest efficacy and highest risk, which of the drug's willingness to pay (WTP) price is closer to the actual amount of the medication, as well as the demographic factors that influence WTP of antipsychotic medications. Methods: WTP instrument was administered to 706 consenting patients. The characteristics ranging from efficacy, duration of administration, and possibility of eliciting side/adverse effects of the drugs was provided. A contingent valuation method was used where a virtual market scenario of 20 payment options was presented to the patients with different prices ranging from N 100 ($ 0.33) to NGN5000 (USD16.67). As at the time of this study, $1 (USD) was equivalent to N300.00 (NGN). A linear multivariate analysis was employed to determine the influence of sociodemographic factors on WTP. Results: At most of the given prices, more patients were willing to pay for the hypothetical antipsychotic D. The WTP for all the medications except haloperidol indicated by most of the respondents were above their reference prices. Longer duration of previous treatment, higher educational status, higher income, and stable marital status gave P = 0.001, P = 0.015, P < 0.001, and P = 0.002, respectively. Conclusion: Patients preferred the medication that has the highest efficacy and attendant risk; majority of the patients are willing to pay at a lower price than the prevailing price for all medications used except haloperidol. The duration of previous drug treatment, income, age, education, and marital status significantly affected the WTP of drugs.

How to cite this article:
Edefo WJ, Usifoh SF, Udezi WA. Willingness to pay for antipsychotic medications in two tertiary health institutions in Nigeria.N Niger J Clin Res 2019;8:97-103

How to cite this URL:
Edefo WJ, Usifoh SF, Udezi WA. Willingness to pay for antipsychotic medications in two tertiary health institutions in Nigeria. N Niger J Clin Res [serial online] 2019 [cited 2020 Jan 26 ];8:97-103
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Full Text


Schizophrenia is one of the major psychiatric disorders that affect the mental health of any individual. Schizophrenia is a chronic and severe mental disorder affecting more than 21 million people worldwide,[1] with an average prevalence of 3.1/1000 and incidence rates in the range of 0.16 and 0.42/1000.[2] Schizophrenia is a psychiatric condition where the sufferer is bewildered with symptoms such as delusions, hallucinations, or disorganized speech as well as negative symptoms, for example, social withdrawal or severely disorganized or catatonic behavior. To be diagnosed with schizophrenia, the individual must suffer from two of these symptoms over much of the time of at least 1 month, with a significant impact on social or occupational functioning for at least 6 months.[3]

People with schizophrenia are 2–3 times more likely to die early than the general population. This is often due to preventable physical diseases such as cardiovascular disease, metabolic disease, and infection.[1] Schizophrenia is a treated condition with medications called antipsychotics and psychological intervention.[1] More than half of the number of schizophrenics are not receiving appropriate care.[1],[4] About 90% of poorly managed condition of schizophrenia live in low- and middle-income countries like Nigeria, this is partly due to lack of access to mental health service, availability and affordability of antipsychotics which are use in managing the condition.[1],[4]

Antipsychotics are broadly divided into two groups, namely, typical and atypical antipsychotics, in spite of this classification, there are pharmacological differences not only between the two groups but within the groups.[5],[6] These medications have side/adverse effects that patients have to tolerate for their lifetimes such as dystonia, tardive dyskinesia, hypotension, hyperglycemia, dyslipidemia, tremor, dry mouth, blurred vision, and weight gain. The degree of severity of these side/adverse effects varies from one antipsychotic medication to another antipsychotic, thus, patients preference for certain antipsychotic due to their ability to cope with these medications is of great concern.[5],[6]

Willingness to pay (WTP) is a reflection of the maximum amount a consumer thinks a product or service is worth. It is considered when developing and asking for products and services; although it is important to note that WTP is not the final arbiter of pricing for individual consumers. It varies depending on their personal assessment of the product or service value. In health care, WTP instrument is used to measure health benefits and investigate patient's values of health intervention or technology.[7],[8],[9]

WTP has also been used among patients with various diseases to measure how much they value improvement in their health. However, among outpatients with schizophrenia whose mental status has been stabilized, WTP has been used also to specifically estimate valuation and preferences of health states related to the efficacy and side effects of antipsychotic medications.[10]

A high percentage of Nigerians is unemployed, and only about 5% have health insurance; thus payment for health care is mostly out of pocket which makes it more difficult for patients to pay for schizophrenia treatment. WTP study, which is scarce in Nigeria, will help to ascertain what schizophrenics are willing to pay for antipsychotics. If what patients are willing to pay is less than the current market price which is the reference price (RP) then subsidization will be needed.[11]

Nigeria, being an oil-rich country, has proceeds that have not positively trickled down to the lives of the citizens, a place where about half of her populace still live on less than USD 2/day.[12] Economists generally believed that people, not the government, are the best decision-makers of what they want. Thus, the theory of economic valuation is based on individual preferences and choices. Individuals revealed their preferences through the choices and tradeoffs that they make, given certain constraints, such as those on income or available time.[13]

Hence, the objectives of this study are to determine patient's preference in three antipsychotic medications with different attributes and side/adverse effects in comparison and a hypothetical antipsychotics medication with highest efficacy and highest risk, which of the drug's WTP price is closer to the actual amount of the medication, as well as the demographic factors that influence WTP of antipsychotic medications.


Design of the study

The study was conducted in two tertiary hospitals in Benin City. The city is located in the south southern part of Nigeria with a population of over 1.2 million people from 2006 national population census commission's report.[14] The health facilities employed in the study are Federal Neuro-Psychiatric Hospital, Benin City (FNPH), a specialized tertiary hospital, and University of Benin Teaching Hospital, Benin City (UBTH). Both health facilities are government-owned facilities that manage mental and/or psychiatric cases in the area and environs such as Ondo, Delta, Anambra states. The institutions have consultant psychiatrists, physicians, pharmacists, nurses, psychologists, sociologists, and occupational therapists in their employment.

Ethical approval for the study was granted by the two health institutions. The reference no for the psychiatric hospital is PH/A.864/vol.vii/12 while that of UBTH is ADM/E22/A/vol.vii/1422.

A convenient sampling technique was used to select the schizophrenic patients who have been on antipsychotic for more than 6 months, are above 18 years, who were willing to participate in the study and have enough experience with the ailment and medications to ensure better cost valuation for the study and who also gave informed written consent.

Data were collected by administering the WTP questionnaire to consecutive patients in the pharmacy waiting area of the psychiatric clinics. Before the questionnaires were administered, the content of the consent form was clearly read out and explained to each patient with an opportunity for them to ask questions to clear up any misconceptions. Interpreters were used to clearly explain the content of the consent form to illiterate persons. All participants were assured of the confidentiality of the information provided. The questionnaire was anonymous and self-administered except for illiterate patients that were assisted by their caregivers who were also taught the relevance and the content of the questionnaire used.

A panel of assessors with a minimum of 4 years practice experience, comprising of one psychiatrist, two pharmacists, and one researcher was formed, the panel identified and discussed the suitability of items included in the questionnaire used in the study.

The WTP questionnaire developed consisted of three parts, the first part contained questions on sex, age, income or allowance per month, marital status, occupation, educational level, number of children, and number of replaced schizophrenic cases since the past 2 years. The patients were asked to indicate how many times they had come for antipsychotic refills in the past 6 months, how much they spent on antipsychotics at their last clinic visit and if they had ever been hospitalized for any psychiatric condition.

The second part of the instrument consists of a detailed description of three antipsychotic medications and a fourth hypothetical medication (which were coded antipsychotic A, B, C, and D) with different attributes, namely, efficacy of the medication, duration of therapy, and possibility of exhibiting adverse drug effects.

In the third part, a virtual market or pharmacy scenario was created with the questionnaire where 20 payment options were presented to the patients with different prices ranging from N 100 (USD 0.33) to NGN5000 (USD16.67). The antipsychotics presented to the patients first were rotated for different patients to eliminate bias before they were asked to make a choice from the four medications based on their attributes. Respondents were asked to indicate how much they were willing to pay for each medication and choose their preference out of the four antipsychotics that were coded A, B, C, and D which has similar properties with haloperidol, risperidone, olanzapine, and hypothetical drug respectively.

Antipsychotic A was stated to have 75% efficacy, to be taken for as long as the patient stays alive, 20% possibility of exhibiting extrapyramidal side effects (EPS) such as tremor, akathisia (restless movement), sedation and 5% possibility of eliciting metabolic syndrome (MS) such as diabetes mellitus and dyslipidemia; antipsychotic B was said to have 75% efficacy, taken as long as one is alive, and 10% tendency to elicit each of the EPS and MS while Antipsychotic C has 75% efficacy, to be taken for the remainder of one's life, 5% EPS and 15% MS, then antipsychotic D, the hypothetical drug was placed at 98% efficacy, to be taken for 5 years and 2% agranulocytosis.

The scenario created was such that each patient was asked what was the maximum price you are willing to pay for any of these medications that aid in managing schizophrenia, the respondents chose and signified the amount (starting from the highest amount and then in descending order) they were willing to pay per month for each of the four medications.

Data analysis

The data collected were entered into Microsoft Excel for sorting and checked for accuracy. It was then loaded into SPSS version 22.0 (IBM Software, Chicago, IL, USA) for descriptive and multivariate analysis. Mean WTP with 95% confidence interval was calculated directly from the collected data. Those who were willing to pay for particular antipsychotics (zero WTP) were noted. For each given price, cumulative percentage demand of respondents who indicated that they were willing to pay for particular antipsychotics at that price was determined. A linear multivariate analysis using the amount of WTP of the four medications as the dependent variables and sociodemographic factors as fixed factors (independent variables) was used to investigate the influence of different sociodemographic factors on WTP.

Further analysis on the data to confirm the validity and sensitivity of the study was conducted with GraphPad InStat version 3.06 (Graphpad Software Inc, San Diego, CA, USA), which reports exact P ≤ 0.05.


Seven hundred and six patients who consented were interviewed (comprising 432 from FNPH and 274 from UBTH) resulting in two thousand, eight hundred and twenty four response.

[Table 1] shows that 361 (50.9%) respondents were those who had been on antipsychotic medication for a maximum of 2 years, those who were single in their marital status constituted 455 (64.2%) of the sample, 487 (68.7%) respondents were those who had no child, and then 247 (34.8%) of patients were in the age range of 30–39 years. The number of respondents that stopped at secondary education was 326 (46%), while 74 (10.4%) of those working to make a living were earning an average monthly income of not more than NGN20,000 (USD66.67). Among the participants, 230 (32.4%) indicated that they never had any relapsed psychiatric episode since the past 2 years.{Table 1}

As shown in [Table 2], the economic burden of having antipsychotic medications indicated that 114 (16.2%) of the patients spent less than NGN1000 (USD3.33) on their antipsychotics monthly while 262 (37.1%) respondents had their prescriptions refill for more than two times. Antipsychotic A, B, C, and D demand can be predicted with the equation: y = β ln ln (x) – y where y = demand, x = price; β and γ are constant. = −26.79 for Antipsychotic A, −32.66 for antipsychotic B, −28.64 for antipsychotic C and −23.09 for antipsychotic D while values for γ are 223.89, 274.27, 242.96, and 206.66 for antipsychotic A, B, C, and D, respectively.{Table 2}

As shown in [Figure 1], at median WTP (WTP50%), antipsychotic A, B, C, and D were NGN700 (USD2.33), NGN1000 (USD3.33), NGN900 (USD3.00), and NGN900 (USD3.00) and unknown, respectively.{Figure 1}

From drug market survey in the research settings used, the RP for 2 mg of haloperidol was from NGN300 (USD 1.00) to NGN400 (USD1.33) with average RP or NGN350 (USD 1.17) per month, that of 2 mg risperidone was for NGN2000 (USD6.67) to NGN 3000 (USD10.00) with average RP NGN2500 (USD8.33) per month, then 5 mg of olanzapine was NGN3000 (USD10.00) to NGN4000 (USD13.33) with average RP of NGN3500 (USD11.67) per month, while that of drug D was not gotten due to the fact it is a hypothetical drug.

As shown in [Table 3], respondents showed WTP at NGN350 (USD1.17), the mean RP of haloperidol which has similar properties for antipsychotic A, B, C, and D were 635 (90%), 680 (96.3%), 635 (90%), and 635 (90%), respectively. WTP at NGN2500 (USD8.33) (USD11.67), the mean RP of risperidone that shared similar characteristics with antipsychotic B, 78 (11.4%), 113 (16.0%), 124 (17.56%), and 198 (28.5%) of participants were willing to purchase antipsychotic A, B, C, and D, respectively, while at NGN3500 (USD11.67), at mean RP of olanzapine that has resemblance with drug C, 38 (5.38%), 51 (7.23%), 61 (8.64%), and 135 (19.12%) respondents were willing to pay for antipsychotic A, B, C, and D, respectively then WTP at above NGN4000, 24 (3.34%), 17 (2.24%), 28 (3.97%), and 95 (13.48%) of respondents were willing to pay for antipsychotic A, B, C, and D, respectively.{Table 3}

In [Table 4], the amount respondents were willing to pay for antipsychotic medications were significantly affected by the following factors: duration of treatment the participants were on medications before the study began gave: Pillal's Trace F (24, 1552) =2.144, P = 0.001; age, F (32, 1552) =2.543, P < 0.001; educational status F (28, 1552) =1.680, P = 0.015; income, F (24, 1552) =3.520, P < 0.001; number of relapsed schizophrenic case since the past 2 years, F (12, 648) = 2.15, P = 0.012; having a child or children, F (4, 385) = 3.27, P = 0.011. Whereas, occupation, F (5, 388) =3.123, P = 0.009, and marital status, F (5, 388) =3.962, P = 0.02 only showed significant effect of P ≤ 0.5 on WTP with the Roy's largest root test.{Table 4}

[Table 5] shows that the participants in subgroup of 7–8 years of 1731 ± 272 is the highest WTP while the WTP for drug A is highest for subgroup 40–49 years was 1893 ± 317 and there is a steady increase in WTP from lowest income group of NGN1–20,000 (USD1-66.67), 730.71 ± 339 to the highest income earning group of above NGN80,000 (USD 266.67), with respect to educational status, the highest WTP of 1713 ± 287 was for postgraduate degree holders. Postgraduate degree holder while the WTP of having children gave a value of 1442 ± 223, then the least WTP in the marital status was divorced/separated with a value of 704 ± 225.{Table 5}


Almost the same number of male and female participated in the study; this was not in line with other studies[4],[15] that revealed that there were more male schizophrenic patients than their female counterparts, the reason for this almost equal ratio of male to female proportion may be as a result of the sampling technique employed in the study.

The study revealed that less than one-quarter of the participants were working to earn money, this is in congruent with other studies where they posited that majority of schizophrenic were unemployed.[8],[16],[17] This study discovered that majority of those that were gainfully employed were income earners of NGN20,000 (USD66.67) per month.

Half (353) of the respondents will want to get antipsychotic A, B, C, and D for NGN700 (USD 2.33), NGN900 (USD3.00), NGN900 (USD3.00), and NGN1000 (USD3.33), respectively. This is a far cry from the RPs of these drugs per month except drug A (haloperidol) at minimum effective dose of 2 mg of once-daily dose whose mean RP was NGN350 per month therapy. This indicated that most of these medications were way above the price patients could afford, therefore, government and agencies should look into ways of subsidizing these products Nigeria want to have more schizophrenics being adequately managed then consequently becoming more productive to their communities in particular and Nigeria at large.

The hypothetical drug, i.e., antipsychotic D at WTP NGN3500 which was the amount to buy the most expensive medication which is antipsychotic C had about one-fifth of the respondents (which is the highest) when compared to other medications respondents showed their willingness to purchase, despite its attendant highest risk of the adverse effect of agranulocytosis due to its better efficacy. This risk-taking behavior of respondents to have better treatment outcome was also seen in other work in WTP done in Nigeria[7],[11] and the United States of America.[10]

At any given price with the exception of when the WTP was less than NGN1000, More patients were willing to pay for antipsychotic D compared to other medications. This indicated that people prefer to buy the drug when compared to other drugs. This preference is due to the improved efficacy of the antipsychotic medication. This assertion is in agreement with several works done in Taiwan,[8] Southern Nigeria.[11]

Respondents who had at least graduate level of education indicated a higher amount of WTP in most cases. This is because they have more knowledge about the psychiatric condition and its management had been shown to positively affect the value a respondent places on a medication.[3] Lower income earners opted for lower amount of WTP for the medications in comparison with the higher income earners. This result of this finding is being supported by other researches assertion that income positively affects WTP for goods.[8],[16],[18] Divorced or separated respondents recorded lower value of WTP of medications compared to other marital status in all the medications employed. This can be explained by findings from other researches[18],[19] which recorded that having a stable family bonding has been proven to improve treatment success rate due to the fact they have more psychological and financial support among others.

One of the limitations of the study was the convenience sampling technique that was employed, as using a random sampling technique may produce a slightly different result. More also, the determination of willingness to pay for each of the medication used in the study was with reference to the average market price of minimum effective dose of the drug whereas in real world situations a patient can be placed on a much higher dose of the antipsychotic.


Majority of the patients preferred and are willing to pay more for the drug with the highest efficacy and highest attendant side effect. Most of the respondents were willing to buy all the antipsychotics used in this study except for haloperidol at a lower price compared to what is presently obtainable in the two health facilities. Therefore, there is need for government and donor agencies to look into ways of subsidizing the price of these medications to adequately take care of those suffering from schizophrenia.

Factors such as previous duration of the treatment before the study, age, income, and education significantly affected WTP of the medication used. In addition, marital status, and number of relapse episode of schizophrenia also have a significant impact on WTP of the antipsychotic medications used.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1World Health Organization. Available from: http://www//home/Newsroom/Factsheet/Schizophrenia. [Last accessed on 2019 Jul 03].
2Joel AA, Isu OP, Amazueba AN. Prevalence of schizophrenia among patients admitted into a Nigeria neuro-psychiatric hospital. IOSR J Dent Med Sci 2015;14:9-14.
3van Os J, Kapur S. Schizophrenia. Lancet 2009;374:635-45.
4Isaac M, Chand P, Murthy P. Schizophrenia outcome measures in the wider international community. Br J Psychiatry Suppl 2007;50:s71-7.
5Enato EF, Aina I. Pharmaceutocal care in psychiatric. In: Oparah AC, editor. Essentials of Pharmaceutical Care. Nigeria: All Deals Investment Company Limited; 2010. p. 353-93.
6Sharpe MC, Lawrie SM. Medical psychiatry. In: Nick RC, Brian RW, Stuart HR. editors. Davidson's Principles and Practice of Medicine 21st ed. Edinburgh, New York: Churchill Livingstone; 2010. p. 242-3.
7Usifoh SF, Udezi AW. Willingness to pay for antiglaucoma drugs in two tertiary instituions in Nigeria. J Pharm Allied Sci 2019;16:2974-86.
8Lang HC. Economic grand rounds: Patients' and caregivers' willingness to pay for a cure for schizophrenia in Taiwan. Psychiatr Serv 2005;56:149-51.
9Lökk J, Olofsson S, Persson U. Willingness to pay for a new drug delivery in Parkinson patients. J Multidiscip Healthc 2014;7:431-40.
10Sevy S, Nathanson K, Schechter C, Fulop G. Contingency valuation and preferences of health states associated with side effects of antipsychotic medications in schizophrenia. Schizophr Bull 2001;27:643-51.
11Udezi WA, Usifoh CO, Ihimekpen OO. Willingness to pay for three hypothetical malaria vaccines in Nigeria. Clin Ther 2010;32:1533-44.
12Bukola A. Nigeria Overtakes India in Extreme Poverty Ranking. Available from: https//>africa>Nigeria. [Last accessed on 2019 Jul 03].
13Chumney CG, Simpson NK. Methods and Designs for Outcomes Research. Bathesda MD: American Society of Health-System Pharmacists, 7272 Wilsconsin Avenue; 2009. p. 117-50.
14Report of Nigeria's National Population Commission on the 2006 Census-JStor. Available from: [Last accessed on 2019 Jul 03].
15Esan OB, Ojagbemi A, Gureje O. Epidemiology of schizophrenia – An update with a focus on developing countries. Int Rev Psychiatry 2012;24:387-92.
16Diener A, O'Brien B, Gafni A. Health care contingent valuation studies: A review and classification of the literature. Health Econ 1998;7:313-26.
17Davies LM, Drummond MF. The eco-nomic burden of schizophrenia. Psychiatr Bull 1990;14: 522-5.
18McCreadie RG. The nithsdale schizophrenia surveys. An overview. Soc Psychiatry Psychiatr Epidemiol 1992;27:40-5.
19Klose T. The contingent valuation method in health care. Health Policy 1999;47:97-123.