Depending on what study you look at, this complaint occurs anywhere from 0.3% to as high as 9% of tonsillectomy cases. Dysgeusia after tonsillectomy is felt to be due to a number of different causes including:
1) medication side effect
2) injury to the lingual branch of the glossopharyngeal nerve
3) zinc deficiency
Regardless of the etiology, most cases of post-tonsillectomy dysgeusia spontaneously resolves within a few months without any specific intervention.
However, there are a few things a patient can try that might help accelerate normal taste recovery including:
1) Stopping all unnecessary medications
2) Zinc gluconate 50mg 3 times per day
3) Alpha Lipoic Acid 200mg 3 times per day
4) Rinsing mouth with watered down milk-of-magnesia
5) Chewing non-mint flavored gum
I did want to point out that there are no comprehensive studies to support any of these interventions. But, it certainly can't hurt to try it.
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Taste disorders after tonsillectomy: case report and literature review. Ann Otol Rhinol Laryngol. 2005 Mar;114(3):233-6.
Posttonsillectomy taste distortion: a significant complication. Laryngoscope. 2004 Jul;114(7):1206-13.
Taste disturbance after tonsillectomy and laryngomicrosurgery. Auris Nasus Larynx. 2005 Dec;32(4):381-6. Epub 2005 Jul 19.