Objective: To present a case of chemically induced myotonia occuring as a result of intentional ingestion of trifluoperazine and Defender Australia Bindi plus Clover Lawn WeederR (chlorophenoxy compounds present as 4‐chloro‐2‐methylphenoxyacetic acid (MCPA) as a dimethylamine salt 15% W/V and 3,6‐dichloro‐2‐methoxybenzoic acid (dicamba) 2.5% W/V). To discuss myotonia. Clinical features: A 38 year old man with features suggestive of dystrophia myotonica presented with severe myotonia, urinary retention and dry lips. There was no personal or known family history of this muscular disorder. Intervention: He was treated with 2mgs of intravenous benztropine mesylate, and 50 grams of activated charcoal and 150 mls of 70% sorbitol orally. An indwelling catheter was inserted. Laryngoscopy and upper gastrointestinal tract endoscopy were performed. The myotonia was managed conservatively and complete recovery occurred as evidenced by normal electromyography on day six of his admission. Conclusion: Myotonia is a rare complication of toxin ingestion. In this case, the toxins may have unmasked subclinical dystrophia myotonica or induced myotonia de novo.