Table 3

Adverse effects and reasons for withdrawal and/or dropout

IDAuthorYearAdverse events (n)Reasons for withdrawal
Intervention group (n)Control group (n)
1Roman et al262018Intestinal discomfort (2)Reasons unrelated to the intervention (2)Non-therapeutic adherence (2)
2Farhangi et al212018No serious adverse eventsDid not consume the supplement (1)Received anti-inflammatory medication (2), diet change (1), did not consume the supplement (3)
3Schumann et al*222018FODMAP group: a major depressive episode (1),
a mild self-reported depressive episode (1), unwanted loss of weight (1)
Due to the adverse events (1), scheduling problems (1), compliance (2)Loss of interest (1), scheduling problems (2)
Yoga group: a newly diagnosed deep leg vein thrombosis (1), back pain (1)
4Sawada et al172017Abdominal pain, sleep disturbance, particularly in the placebo groupNo data provided
5Sanchez et al232017No data providedPoor compliance to the treatment (1)
6Romijn et al272017Dry mouth, sleep disruptionAntibiotic use (1), antidepressant use (2), participant choice (4)Antibiotic use (2), stressful life events (1)
7Pinto-Sanchez et al182017No serious adverse events related to study productAntibiotic use (3), antidepressant use (1)Antibiotic use (1), antidepressant use (1)
8Kelly et al202017Side effects were negligibleNo data provided
9Eswaran et al282017No data providedLost to follow-up: not returning calls (1), started antibiotics (1), too expensive (1); discontinued intervention: too limiting (1), moved out of state (1)Discontinued intervention: failed to make symptom reports (2)
10Colica et al292017No data provided2 subjects voluntarily stopped the treatment1 subject voluntarily stopped the treatment
11Azpiroz et al302017Intake of scFOS was well tolerated and the number of adverse events was similar in the scFOS (18) and placebo (21) groups†Colonic lavage prior to the rectal sensitivity test (1), antibiotic treatment (1)
12Lyra et al312016Treatment-emergent AEs: GI disorders, gastroenteritis and influenza
IP-related AEs: mild GI symptoms (7 placebo, 7 low dose and 9 high dose)
Two SAE cases: pneumonia and syncope; neither was associated with the IP or any trial procedure
Low dose—adverse event (4),
lost to follow-up (3), other (4),
protocol violation (1),
withdrawal of consent (5)
High dose—adverse event (10), other (3),
protocol violation (1), withdrawal of consent (4)
Adverse event (3),
lost to follow-up (2),
other (2),
protocol violation (3), withdrawal of consent (6)
13Steenbergen et al322015No data providedNo data provided
14Lorenzo-Zúñiga et al332014No adverse drug reactionsHigh dose: loss to follow-up (3),
discontinued intervention (3)
Low dose: loss to follow-up (3),
discontinued intervention (3)
Loss to follow-up (5),
discontinued intervention (5)
15Peters et al342014No data provided‡No data provided
16Alipour et al352014No adverse effectsDid not follow the study protocol (8/6)
17Yuman and Yingwei362013No data providedNo data provided
18Messaoudi et al192011No data providedNo data provided
19Simrén et al372010No adverse eventsLack of effect of the treatment (5), factors unrelated to the study (2)
20Silk et al382009Moderate diarrhoea (1–3.5 g placebo), mild nausea (1–7.0 g placebo, 1–3.5 g prebiotic)Felt the study was too demanding (3), felt the placebo caused diarrhoea (1), took part in another probiotic study (1), took a commercially available probiotic preparation during baseline (2)
21Rao et al392009No significant adverse eventsReasons unrelated to the intervention (4)
  • GI disorders refer to gastrointestinal tract disorders, including abdominal discomfort, abdominal distension, abdominal pain, constipation, diarrhoea and flatulence.

  • *None of these events were adjudged to relate to the study interventions.

  • †Did not provide details.

  • ‡One patient ceased the whey challenge (treatment first received) prematurely because of intolerable symptoms after lunch on day 2.

  • AE, adverse effect; FODMAP, fermentable oligosaccharides, disaccharides, and monosaccharides and polyols; GI, gastrointestinal ; IP, investigational product; SAE, serious adverse event; scFOS, short-chain fructooligosaccharides.