This qualitative study explored the benefits and challenges experienced by long-term MMT participants in China in the context of the declining MMT population. Participants in this study corroborated the declining trend and considered death, arrest, and self-perceived abstinence as the main causes. In terms of individual treatment, they reported notable improvements in health, family relationships, and social functioning. Despite the positive changes, they also encountered several challenges such as the heavy financial hardship and conflicts between working time and the clinic opening times.

Over the past decade, the number of MMT participants has significantly decreased. According to China CDC [9], there was an almost 20% decrease in MMT participants in 2020, with Guangdong experiencing a sharper decrease compared to other provinces, possibly due to its larger MMT population base and efforts made to heroin control. The participants of this study corroborated the decline and considered death caused by illness as the leading reason. A long history of drug use is strongly associated with life-threatening diseases, such as HIV and cancer, which can hugely impact health among this group. For instance, over 60% of Chinese MMT participants were infected with HCV [11], which could result in liver cancer, the most-mentioned death cause in line with our participants. The risk of getting severe illness will further increase as they get older. Another reason for this decline was the voluntary withdrawal from MMT. Some participants cited no longer being dependent on heroin and chose to quit MMT permanently. However, research suggests that these individuals may have an increased risk of relapse to alternative drugs such as methamphetamine, due to inadequate perception of the benefits of MMT [17, 18]. This situation has also been observed in other countries, including Vietnam and Canada, and has raised great public health concerns [19, 20]. This alerts us to pay more attention to those who voluntarily quit MMT, as well as to strengthen education to existing participants, to prevent relapse, especially to synthetic or new drugs among these groups.

In contrast to the participant’s views, being arrested and sent to the compulsory rehabilitation center was ranked as the top cause of the decrease in Chinese MMT participants during the decade by China CDC [9]. This was only reported by a small proportion of long-term participants in our study, which may be because participants who have undergone long-term MMT are more likely to experience improvements in their social functioning, which resulted in less likely to engage in criminal behavior, compared to the short-term participants.

Long-term participants experienced a range of benefits during their treatment. At the individual level, positive changes in both physical and mental health were most vocalized, which aligns with other studies [21, 22]. Most participants were in poor health at the enrollment of MMT [23] due to their history of drug use. In our study, this included people living with HIV, cancer survivors, and people living with chronic pain. They reported significant improvements in health, including reduced withdrawal syndrome, alleviated pain, and enhanced sleep quality. These positive changes can be attributed to reduced drug use and less high-risk behavior after receiving MMT. Additionally, the health education provided by MMT clinics likely increased their awareness of health issues, resulting in more proactive health-seeking behavior [24]. Furthermore, as a vulnerable group for mental health issues, they experienced a decrease in negative emotions and an increase in self-confidence after being treated. Better health status facilitated their reintegration into society [25], leading to closer family relationships and more employment opportunities. According to Sun et al. [26], the overall employment rate of MMT participants increased from 26.4% at baseline to 41.6% after 6-month treatment and to 59.8% after 12 months. Employment not only alleviated their financial burden but also contributed to improved family relationships and a sense of fulfillment, as indicated by our findings.

Hence, it can be concluded that the effectiveness of MMT extends beyond the realm of individual health improvement. It encompasses various interconnected benefits, including enhancements in health status, interpersonal relationships, and social functioning. These mutually reinforcing advantages create a virtuous circle, leading to an overall improvement in quality of life.

In terms of clinical treatment, participants in this study reported frequent changes in their daily methadone dose during the long-term treatment. Participants with cancer, or pain, or those taking HIV antivirals tended to increase their dose. Methadone has pain-relieving effects and its metabolism can be accelerated by HIV antivirals, necessitating higher doses for these individuals [27]. However, almost every participant expressed a desire for dose tapering and took action toward full recovery from opioid dependency. This is consistent with previous studies, which indicated that around 41–57% of participants tapered their doses [28, 29]. According to our findings, the frequency, speed, and duration of dose tapering varied among participants, with those on relatively higher doses, such as over 100 mg per day, being more adaptable to larger decreases. People who added doses due to temporary illness would decrease the dose as usual once they felt better. Participants on lower doses, such as 5–10 mg per day, found it challenging to adjust to the side effects, particularly insomnia if they decreased the dose too much or too quickly. In light of these findings, it is important to establish official dose adjustment guidelines for Chinese participants, considering individual adaptation [30].

Apart from all the improvements, participants also highlighted the challenges they faced throughout their treatment, including conflicts between the opening hours of clinics and working schedules, the fear of treatment discontinuation, economic hardship, and the lack of dose adjustment guidelines and discrimination.

Another challenge was that most MMT clinics had opening hours that overlapped with normal working hours. This made it difficult for participants to arrive at work on time and limited their job options. This conflict exacerbated their economic hardship as they had to choose jobs near the clinic or opt for night shifts to maintain the treatment. Participants may be more likely to drop out of MMT due to this conflicted schedule [29].

Although negative effects such as decreased clinic visits and increased levels of anxiety and depression among participants were reported when COVID-19 first broke out in 2019 [31], a limited impact was reported since the pandemic was relatively well-controlled in Guangdong, especially in the less-populated areas. Most clinics opened as usual, and measures such as medication delivery by police officers or community workers were implemented for those in quarantine [32]. Other countries, however, tended to liberalize the taking-home policy as the response [33, 34]. Despite the limited impact, challenges relating to treatment discontinuity and its negative impact on income emerged as the most significant concerns, as revealed by our findings. These challenges also triggered participants’ pre-existing mental disorders [35]. Additionally, emergencies such as hospital admissions could disrupt the continuity of MMT. The current policies and processes for accessing medication vary across regions, and participants expressed complaints about the cumbersome process of applying for dose delivery to the hospital. Hence, there is an urgent need to develop official guidelines or manuals for the preparedness for emergencies that are feasible and accessible for both participants and staff.

Moreover, discrimination from employers was also reported and caused economic hardship. Participants shared their experiences of being refused employment due to their identification as PWUD; meanwhile, the unemployed participants were more likely to experience discrimination from the public [36]. This contradiction further hindered the progress of their return to normal life. All of the above indicates that economic hardship is a priority challenge to be addressed for this group [37, 38], as they sought a more comprehensive return to normal life, beyond simply being abstinent from addiction. Therefore, targeted interventions should primarily focus on helping long-term participants resume social functioning. Simultaneously, improving adherence to MMT should remain a key area of focus for short-term participants.

To address all the challenges identified, our participants provided several possible solutions. For MMT clinics, they suggested that the opening hours should be extended or staggered to accommodate commuting time, ensuring both timely treatment and arrival at work. Another expectation of participants was to lower the cost of treatment, or even provide it for free, considering their financial hardship.

In term of improving the effectiveness of MMT, they emphasized the importance of health education and thought it should be integrated to the daily treatment to help the peer develop a proper understanding of MMT, reducing relapses and dropouts. As for the discontinuation of treatment, they believe narcotics control departments or CDC should develop comprehensive official guidelines to respond to emergencies, or simplify the current process, making it more feasible and operable for both clinic staff and participants.

They also expect a platform for job hunting without disclosing their drug use history. Providing a basic living allowance or offering jobs to eligible people should also be considered to alleviate their financial burden, based on the participants.

In summary, the clinic could improve the flexibility of opening hours and continue related interventions to ensure the effectiveness of MMT; narcotics control departments or CDC are expected to developed a feasible and simple process for MMT under emergency; relevant public sectors are responsible to create more jobs or individualized supporting plans for participants experiencing poverty.