1. A method of treating fibromyalgia syndrome, comprising administering a therapeutically effective amount of a substance having structural formula (1), or a pharmaceutically acceptable salt thereof, to a mammal in need of treatment, wherein R is selected from the group consisting of hydrogen, lower alkyl, containing from 1 to 8 carbon atoms, a halogen selected from F, Cl, Br and I, an alkoxy group containing from 1 to 3 carbon atoms, a nitro group, a hydroxy group, trifluoromethyl, and a thioalkoxy group containing from 1 to 3 carbon atoms； x represents integer from 1 to 3, provided that R may be the same or different when x is 2 or 3； R and R may be the same or different from each other, and they are independently selected from the group consisting of hydrogen, lower alkyl, containing from 1 up to 8 carbon atoms, aryl, arylalkyl, cycloalkyl containing from 3 to 7 carbon atoms； R and R can be combined to form a 5-7 membered heterocycle substituted by a member selected from the group consisting of hydrogen, alkyl and aryl groups, and a heterocyclic compound contains from 1 to 2 nitrogen atoms and from 0 to 1 oxygen atoms and nitrogen atoms are not directly bonded to each other or to the oxygen atom. 2. The method of claim 1, wherein R is hydrogen and x is 1.3. The method of claim 1, wherein R, R and R are hydrogen and x is 1.4. The method according to claim 1, wherein the substance having the structural formula (1) is an enantiomer that essentially does not contain other enantiomers, or an enantiomeric mixture in which one enantiomer of a substance having the structural formula (1) predominates. The method according to claim 4, in which one enantiomer in1. Способ лечения синдрома фибромиалгии, содержащий введение терапевтически эффективного количества вещества, имеющего структурную формулу (1), или его фармацевтически приемлемой соли, млекопитающему, нуждающемуся в лечении,причем R выбран из группы, состоящей из водорода, низшего алкила, содержащего от 1 до 8 атомов
