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. 2023 Mar 3;120(9):146–154. doi: 10.3238/arztebl.m2022.0411

eTable 4. Evidence for the efficacy of olfactory training in the treatment of olfactory dysfunction.

Author Design Study participants Clinical endpoint Results
Pieniak et al.,
2022 (e108) 		Review n = 3134
(PIOD, PTOD, IOD, sinunasal, IPD, medication, elderly)
Review: 48 studies 		Sniffin’ Sticks or other psychophysical tests Improvement of olfactory function in all patient groups except for sinunasal etiology, ‧greatest efficacy for discrimination and identification
Yaulaci et al.,
2022 (e109) 		Prospective, non-randomized study n = 51 (PIOD)
1) Olfactory training
2) No treatment for 12 weeks 		Sniffin’ Sticks Clinically significant improvement in 40% of training group versus 6% of control group
Lechner et al.,
2022 (e110) 		RCT n = 63 (PIOD)
1) Olfactory training
2) No treatment for 12 weeks 		Brief Smell Identification Test (BSIT) Non-significant improvement of BSIT score in training group versus control group, ‧OR 2.38
Choi et al.,
2021 (e111) 		Prospective, non-randomized study n = 104 (PIOD)
1) Olfactory training
2) No treatment for 3 months 		Sniffin’ Sticks Significant improvement of TDI, threshold, and identification in training group
Qiao et al.,
2020 (e112) 		RCT n = 125 (PIOD)
1) Olfactory training
2) Training with household odors (e.g., perfume, vinegar) for 24 weeks		 Sniffin’ Sticks Significant improvement of TDI, discrimination, and identification in both groups
Saatci et al.,
2020 (e113) 		RCT n = 60 (PIOD)
1) Olfactory training (4 odors)
2) Training ball with 4 odors for 12 weeks		 Sniffin’ Sticks Significant improvement of TDI, discrimination, and identification in both groups
Kattar et al.,
2020 (e114) 		Systematic review and meta-analysis n = 990 (PIOD)
Review: 16 studies; meta-analysis: 4 studies 		Sniffin’ Sticks Significant improvement in all studies, OR 2.77
Sorokowska et al.,
2017 (e70) 		Systematic review and meta-analysis n = 1005 (PIOD, PTOD, IOD, sinunasal, IPD, elderly) Meta-analysis: 13 studies Sniffin’ Sticks Significant association between training and improvement of TDI (g = 1.10), discrimination (g = 0.89) and identification (g = 0.83)
Pekala et al.,
2016 (e115) 		Systematic review and meta-analysis n = 639 (PIOD, PTOD, IOD, sinunasal, IPD, elderly) Review: 10 studies; meta-analysis: 3 studies Olfactory improvement using psychophysical tests Significant association between training and improvement of TDI, discrimination, and identification, OR 2.75
Jiang et al.,
2019 (e116) 		RCT n = 111
(PTOD)
1) Olfactory training (4 odors)
2) Olfactory training (1 odor – PEA) for 6 months 		UPSIT
PEA threshold 		Significant improvement of PEA threshold in both groups, UPSIT improvement only in PEA group
Langdon et al.,
2018 (e117) 		RCT n = 42 (PTOD)
1) Olfactory training (6 odors)
2)  No treatment for 12 weeks 		Barcelona Smell Test
Butanol threshold test
VAS 		Significant improvement in training group compared with control group for threshold test; no change in VAS, Barcelona Smell Test
Oleszkiewicz et al.,
2018 (e118) 		RCT n = 108 (PIOD, IOD)
Olfactory training with
1) 4 odors
2) 4 odor combinations
3) 3 × 4 odors, changed every 2 months 		Sniffin’ Sticks Significant improvement of TDI, threshold, and identification in all groups, no effect of training procedure
Patel et al.,
2017 (e119) 		RCT n = 43 (PIOD, IOD)
1) Olfactory training (4 odors)
2) No treatment for 6 months		 UPSIT Significant in 32% of the training group (versus 13% in control group)
Damm et al.,
2014 (e72) 		RCT n = 171 (PIOD)
1) Olfactory training with high-concentration odors
2) Olfactory training with low-concentration odors Cross-over after 18 weeks 		Sniffin’ Sticks Significant improvement of TDI in 26% of the training group with high-concentration odors (versus 15% in group with low-concentration odors)
Poletti et al,
2017 (e120) 		Prospective, pseudo-randomized study n = 96 (PIOD, PTOD)
Olfactory training with
1) 4 high-molecular odors
2) 4 low-molecular odors for 5 months 		Sniffin’ Sticks Significant improvement of TDI in both groups, high-molecular odors associated with significantly better threshold in PIOD
Konstantinidis et al.,
2016 (e121) 		Prospective, partially randomized study n = 111 (PIOD)
1) Olfactory training for 16 weeks
2) Olfactory training for 56 weeks 3) No treatment		 Sniffin’ Sticks Significant improvement of TDI in training groups compared with controls; highest increase in long-term group (9.1 for 16 weeks, 11.4 for 56 weeks)
Gellrich et al.,
2018 (e122) 		Prospective cohort study n = 30 (PIOD)
1) Olfactory training for 12 weeks 		Sniffin’ Sticks
Gray matter (GM) volume on MRI 		Significant improvement of TDI and significant GM volume increase in hippocampus, thalamus, and cerebellum
Hummel et al.,
2018 (e123) 		Prospective cohort study n = 23 (PIOD, IOD)
1) Olfactory training for 4–6 months 		Sniffin’ SticksEOG Significant improvement in identification, but not in TDIEOG response significantly improved by training
Altundag et al.,
2015 (e71) 		Prospective cohort study n = 85 (PIOD)
1) Olfactory training with 3 sets of 4 odors
2) Olfactory training with 4 odors
3) No treatment for 36 weeks		 1) Sniffin’ Sticks
2) VAS 		Significant improvement of TDI in training groups compared with controls, with greatest improvement rate in group with changing odors (TDI 8.2 versus 6.1 versus 1.7)
Konstantinidis et al.,
2013 (e73) 		Prospective cohort study n=119 (PTOD, PIOD)
1) Olfactory training (4 odors)
2) No olfactory training for 4 months 		Sniffin’ Sticks Significant improvement of TDI in training groups compared with controls, particularly in PIOD (TDI 6.25 versus 1.5 PIOD, 5.1 versus 1.2 PTOD)
Haehner et al.,
2013 (e124) 		Prospective cohort study n = 70 (PD)
1) Olfactory training
2) No training 		Sniffin’ Sticks Significant improvement of TDI and discrimination in training group compared with controls (TDI by 2.4 versus −0.6)
Hummel et al.
2009 (e125) 		Prospective cohort study n = 56 (PIOD, PTOD, IOD)
1) Olfactory training
2) No treatment for 12 weeks		 Sniffin’ Sticks Significant improvement of TDI and olfactory threshold in training group compared with controls

EOG, Electro-olfactogram; IOD, idiopathic olfactory dysfunction; IPD, idiopathic Parkinson’s disease; PIOD, postinfectious olfactory dysfunction; PTOD, post-traumatic olfactory dysfunction;

RCT, randomized controlled trial; TDI, summed score olfactory threshold + discrimination test + identification test; UPSIT, University of Pennsylvania Smell Identification Test