600 mg per day orally for 20 days followed by 200 mg per day for 10 days.
α-Lipoic Acid can be bought online far cheaper than from high street shops. I normally point people to the Healthspan website as it seems reliable and reasonably priced. Healthspan sells the α-Lipoic Acid together with acetyl-L-carnitine under the name of Lipocarn. Obviously, if you can find a better (and cheaper) supplier, use them!
Minerva Stomatol 2002 Sep; 51 (9):405 - 409. Femiano F. Burning Mouth Syndrome (BMS): an open trial of comparative efficacy of alpha-lipoic acid (thioctic acid) with other therapies.
Oral Dis 2000 Sep; 6 (5): 274 - 277. Femiano F, Gombos F, Scully C, Busciolano M, Luca PD. Burning Mouth Syndrome (BMS): controlled open trial of the efficacy of alpha-lipoic acid (thioctic acid) on symptomatology.
Int J Oral Maxillofac Surg 2002 Dec; 31 (6): 625 - 628. Femiano F, Scully C, Gombos F. Idiopathic dysgeusia; an open trial of Alpha Lipoic Acid (ALA) therapy.