Secretin and Autism Ranking:

Status Research

There are a number of limitations to all of the research studies published to date. It is worth noting that the study by Horvath et al, 1998 which initiated the huge interest in secretin, was a particularly poor study. 

Type of study

• Four of the studies (Horvath et al, 1998, Lightdale et al, 2001; Lonsdale and Shamberger, 2000; Robinson 2001) used single-case designs, that is, they did not have a control group of participants who did not receive the intervention 
• The study by Horvath et al, 1998 was a retrospective case series which used no form of experimental control. This is an especially weak design.
• Some of the randomised controlled studies did not appear to follow or report all of the protocols expected within randomised controlled studies. For example, the study by Chez et al, 2000 did not adequately explain how the participants were randomised to the different groups. The study by Sandler et al, 1999 did not provide sufficient details about the allocation concealment (the way in which the participants and researchers were kept blind as to which participant received which intervention). The study by Carey et al, 2000 provided insufficient outcome data.

Participants

• One of the single case designs (Horvath et al, 1998) included only three children. It also only included children with specific symptoms (diarrhoea) who had been admitted to hospital for a specific medical procedure (a gastrointestinal endoscopy).
• Seven of the group studies included fewer than 30 participants and three of these group studies (Carey et al, 2002; Handen et al, 2005; Sponheim et al, 2002) included fewer than 10 participants.
• One of the studies (Lonsdale, 2000) had a very high dropout rate, with 16 participants (25% of the total) not completing the study.
• Some of the studies were restricted to specific groups of participants. For example, the study by Owley et al (2001) looked only at children diagnosed with autistic disorder rather than at adolescents or at children diagnosed with other forms of autism.

Intervention/s

• Some of the studies did not provide enough details about the experimental intervention. For example, Lonsdale and Shamberger, 2000 stated that the participants received a single vial of secretin but they did not state what type of secretin was used and they did not state the dosage in the vial.
• Most of the studies used a single dose of secretin and/or a single dose of the placebo - although this was in line with the anecdotal claims for how secretin is supposed to work.
• Most of the studies which used more than one dose of secretin ran for relatively short periods of time (four to eight weeks). 
• Some of the studies (such as Chez et al, 2000) examined many participants who were receiving other medications or other forms of intervention at the same time as they received the secretin. 
• Some of the cross-over trials had relatively short wash-out periods between interventions (one or two weeks) but one cross-over trial (Sponheim et al, 2002) had no wash-out period at all between interventions.
• The infusion of secretin in the study by Horvath et al (1998) took place alongside an endoscopy delivered under full anaesthetic which could have influenced the outcome of the study.

Comparators

• Many of the studies compared an experimental group (who received the secretin) with an experimental group (who received the placebo). However, in some studies, the participants in the experimental group were different to the participants in the control group. For example, in the study by Coniglio et al, 2001, the children in the experimental group had lower total language-age scores at intake than the children in the control group.

Outcomes

• The study by Horvath et al (1998) had a number of significant flaws in terms of how it reported the outcomes. For example only two of the three participants were assessed using standardised outcomes measures; outcome (and baseline) data were not provided from any of those standard measures; the study did not provide any data within table 3, which supposedly reported on changes in the core features of autism; the study combined data from a range of sources in table 4 but did not state which, making it impossible to assess that data or compare it with other studies
• Some of the studies did not provide enough detail about the outcomes for us to be able to make a considered assessment. For example, the study by Lonsdale, 2002 reported that there were 39 participants whose “clinical response varied from minor to major behavioral and/or bowel function improvement”. However the study did not provide any details on what those behavioural or bowel function improvements were.
• Some of the studies used a small number of outcome measures. For example, Carey et al (2002) used only one outcome measure, the Aberrant Behavior Checklist.
• Other studies did not use standardised, widely accepted outcome measures. For example, the study by Lonsdale and Shamberger, 2000 used only one behavioural outcome measure, which was a highly subjective, non-validated form on which the parents were asked to survey each of the listed symptoms and apply a numerical score on a weekly basis throughout the period of surveillance.
• Most of the studies did not use a standardised measure of adverse effects (such as the Treatment Emergent Symptoms Scale) and some of the studies (Lightdale et al 2001) did not report whether there were any adverse side effects.  
• Most of the studies did not identify if secretin had any beneficial effects in the medium to long term (six months or longer). For example, Corbett et al, 2001 carried out a single assessment of the outcomes and did so only one week after administration of the secretin.

Other

• Very few of the studies appeared to involve autistic people and parents and carers in the design, development and evaluation of those studies.

For a comprehensive list of potential flaws in research studies, please see ‘Why some autism research studies are flawed’

Updated

16 Jun 2022

Last Review

01 Dec 2018

Next Review

01 Aug 2024