Are we properly assessing the acceptability of mental health interventions from a service user's point of view? A treatment can be efficacious and effective but still not acceptable to a service user. For example, someone with psychosis may find a treatment that improves symptoms but causes significant weight gain and sedation unacceptable. Despite significant progress being made in developing safe and effective interventions for mental health problems, a notable proportion of people remain in need. The reasons for this are complex. Part of the problem could be an inadequate focus on how 'acceptable' interventions really are to service users given their views and specific circumstances.Treatment acceptability has been a rather poorly defined concept. This has led to researchers using several methods to assess their own ideas about what service user acceptability is. This can include methods such as using recruitment and withdrawal data. But such data may not be true markers of acceptability to a service user.Current approaches to assessing acceptability need improvement. Existing acceptability questionnaire measures are not widely used and are often developed for specialist settings. Crucially, very few have had any stated involvement of people with mental health conditions in their development. This approach risks not listening to service users' voices fully.Developing better ways of understanding and assessing service users' views of treatment acceptability in mental health could have many benefits-including empowering individual service users to identify interventions that they can and cannot accept. It is time to better understand what 'acceptable' really means in mental health.