the term “ about ” generally means within 10 %, preferably within 5 %, and more preferably within 1 % of a given value or range . with regard to a given value or range in degrees 2θ from xrpd patterns , the term “ about ” generally means within 0 . 2 ° 2θ and preferably within 0 . 1 °, 0 . 05 °, or 0 . 01 ° 2θ of the given value or range . alternatively , the term “ about ” means within an acceptable standard error of the mean , when considered by one of ordinary skill in the art . the term “ treat ” as used herein refers to preventing , ameliorating , controlling , or curing the desired symptoms or disorders . the term “ venlafaxine hydrochloride ” as used herein refers to racemic mixtures of r and s - venlafaxine and their optically pure enantiomers . the crystalline polymorph of the present invention may be r , s , or a racemic mixture of r and s - venlafaxine hydrochloride . the term “ monohydrate ” as used herein refers to a hydrate in which one molecule of water is associated with each molecule of venlafaxine hydrochloride . the term “ venlafaxine hydrochloride monohydrate ” as used herein refers to a monohydrate of venlafaxine hydrochloride ( c 17 h 27 no 2 . hclh 2 o ) having an xrpd pattern substantially identical to that shown in fig1 or fig6 designated as “ monohydrate ”. peak locations and intensities for the xrpd pattern in fig1 are provided in table 1 below . in particular , the peaks ( expressed in degrees 2θ ) at about 7 . 45 , 8 . 60 , 14 . 95 , 18 . 02 , 21 . 41 , 27 . 07 , 32 . 74 , and 34 . 60 are unique to venlafaxine hydrochloride monohydrate . venlafaxine hydrochloride monohydrate has a molecular weight of about 331 . 88 g / mol . it also has a dehydration endotherm , according to dsc , at about 85 ° c . and a melting endotherm , according to dsc , at 219 - 221 ° c . venlafaxine hydrochloride monohydrate generally loses the hydration water at less than 10 % relative humidity to form an anhydrous form . the anhydrous form of the crystalline polymorph generally converts to the monohydrate at greater than 10 % relative humidity . the crystalline polymorph of the present invention is useful for treating , preventing , or controlling depression and the aforementioned indications . the appropriate dosage amounts for an animal can be determined by methods known in the art . generally , a therapeutic effective amount for the desired purpose is administered . the dosage of the crystalline polymorph of venlafaxine hydrochloride disclosed herein is generally from about 75 to about 300 mg per day . the crystalline polymorph can be formulated into a pharmaceutical composition . preferably , the pharmaceutical composition comprises an amount of the crystalline polymorph of venlafaxine hydrochloride effective to treat the desired indication in an animal , such as a human . according to one preferred embodiment , the pharmaceutical composition comprises at least about 20 , 30 , 40 , 50 , 60 , 70 , 80 , 90 , 95 , 96 , 97 , 98 , 99 , 99 . 1 , 99 . 2 , 99 . 3 , 99 . 4 , 99 . 5 , 99 . 6 , 99 . 7 , 99 . 8 , or 99 . 9 % by weight of venlafaxine hydrochloride monohydrate , based upon 100 % total weight of venlafaxine hydrochloride in the pharmaceutical composition . according to yet another preferred embodiment , the pharmaceutical composition comprises at least about 20 , 30 , 40 , 50 , 60 , 70 , 80 , 90 , 95 , 96 , 97 , 98 , 99 , 99 . 1 , 99 . 2 , 99 . 3 , 99 . 4 , 99 . 5 , 99 . 6 , 99 . 7 , 99 . 8 , or 99 . 9 % by weight of venlafaxine hydrochloride monohydrate , based upon 100 % total weight of crystalline venlafaxine hydrochloride in the pharmaceutical composition . the pharmaceutical composition can also be substantially free or completely free of other crystalline polymorphs of venlafaxine hydrochloride , such as forms i and ii . for example , the pharmaceutical composition can contain the monohydrate form in substantially pure form . the terms “ substantially free ” and “ substantially pure ” include those pharmaceutical compositions that contain less than 0 . 01 , 0 . 1 , 0 . 2 , 0 . 3 , 0 . 4 , 0 . 5 , 1 or 2 % by weight of other crystalline polymorphs , such as form i or ii or both , based upon the total weight of pharmaceutical composition ( or alternatively based upon on the total weight of venlafaxine hydrochloride in the pharmaceutical composition ). according to one embodiment , the pharmaceutical composition contains from about 25 to about 350 mg of the crystalline polymorph of venlafaxine hydrochloride . more preferably pharmaceutical compositions of the present invention contain 75 mg , 150 mg or 225 mg of the crystalline polymorth of venlafaxine hydrochloride . the pharmaceutical composition may also include one or more pharmaceutically acceptable carriers or diluents ( e . g . water and organic solvents ) and excipients . the term “ excipient ” includes , but is not limited to , those materials that are acceptable for use in pharmaceutical formulations , and are added to the formulation to promote the stability and viability of the formulation , such as binders , bulking agents , clarifying agents , buffering agents , wetting agents , lubricants , sweeteners , and flavoring agents . suitable excipients include , but are not limited to , cellulose , ethyl cellulose , gelatin , hydroxypropyl methylcellulose , iron oxide , titanium dioxide , lactose , magnesium stearate , and sodium starch glycolate . suitable pharmaceutically acceptable carriers , diluents , and excipients also include those described in remington &# 39 ; s , the science and practice of pharmacy , ( gennaro , a . r ., ed ., 19 th edition , 1995 , mack pub . co .) which is herein incorporated by reference . the phrase “ pharmaceutically acceptable ” refers to additives or compositions that are physiologically tolerable and do not typically produce an allergic or similar untoward reaction , such as gastric upset , dizziness and the like , when administered to an animal , such as a mammal ( e . g ., a human ). according to one preferred embodiment , the pharmaceutical composition is an extended release formulation , such as that described in u . s . pat . no . 6 , 274 , 171 , which is herein incorporated by reference . for example , an extended release formulation may comprise spheroids comprised of the crystalline polymorph of the present invention , microcrystalline cellulose , and , optionally , hydroxypropyl - methylcellulose . the spheroids are preferably coated with a film coating composition comprised of ethyl cellulose and hydroxypropylmethylcellulose . the pharmaceutical composition may be a dosage form , such as a liquid ( e . g ., elixirs and suspensions ), capsule , pill , or tablet . the pharmaceutical compositions and the crystalline polymorphs of venlafaxine hydrochloride may be administered to animals , including , but not limited to , mammals ( e . g . humans ), orally , intravenously , intramuscularly , parenterally intraperitoneally , subdermally , buccally , subcutaneously , transdermally , topically , rectally , vaginally , or intranasally . preferably , the composition is administered orally . the venlafaxine hydrochloride monohydrate can be prepared by wet granulating form i or ii of venlafaxine hydrochloride or a mixture thereof . it can also be prepared by recrystallizing form i or ii of venlafaxine hydrochloride or a mixture thereof from water or a mixture of water and an organic solvent . a non - limiting example of a suitable organic solvent is ethanol . venlafaxine hydrochloride may be prepared by any method known in the art including , but not limited to , the methods described in u . s . pat . nos . 4 , 535 , 186 and 4 , 761 , 501 and international patent publication nos . wo 00 / 32555 , wo 00 / 32556 , and wo 01 / 07397 , all of which are hereby incorporated by reference . the crystals formed may be recovered by any method known in the art , such as filtration , centrifugation , or with a buchner style filter , rosenmund filter , or plates and frame press . typically , the crystals are recovered as solids . the following examples are illustrative and are not meant to limit the scope of the claimed invention . the venlafaxine hydrochloride which is used as a raw material in the example below can be prepared by any method known in the art . approximately 1 . 5 ml of water was heated in a beaker to near its boiling point and about 3 g of venlafaxine hydrochloride of form i or form ii were added . the suspension was stirred with heating until all of the venlafaxine hydrochloride was dissolved . the resulting clear solution was slowly cooled down to ambient temperature . the solution was stored at 5 ° c . to allow the monohydrate to crystallize . the crystals were removed from the beaker onto filter paper and exposed to the air for about 8 hours to dry . the final product was ground and stored in sealed glass vials . the product was an odorless , white to off white crystalline powder and had a melting point , as measured by dsc , of ˜ 219 ° c . dsc measurements were carried out in both sealed pan and vented pan at a scan rate of 10 ° c ./ minute from 25 ° c . to 240 ° c . under a nitrogen purge with a pyris i dsc available from perkin - elmer of shelton , conn . the dsc scans with the sealed pan and the vented pan are shown in fig2 and 3 , respectively . fig2 shows a small endotherm at 82 ° c . and a large endotherm at 93 ° c . ( heat of fusion is 41 j / g ), which was the melting of the venlafaxine hydrochloride monohydrate . fig3 shows three endotherms . the first is a broad endotherm at 106 ° c ., which was due to the dehydration and evaporation of water from the sample . the second is a small endotherm at 196 ° c . corresponding to a solid - solid phase transition . the third is a large endotherm at 221 ° c ., which was the melting of the anhydrous venlafaxine hydrochloride . the onset melting temperature for venlafaxine hydrochloride was 219 ° c . ( heat of fusion is 105 j / g ). a sample of venlafaxine hydrochloride monohydrate was heated from 25 to 230 ° c . at a scan rate of 10 ° c ./ minute in a pyris i tga , available from perkin - elmer of shelton , conn ., under a nitrogen purge . the results are shown in fig4 . at 125 ° c ., the sample lost 5 . 37 % of its weight . the theoretical amount of water in venlafaxine hydrochloride monohydrate is about 5 . 4 % by weight . therefore , this tga result agrees with that of a monohydrate of venlafaxine hydrochloride . a water vapor sorption / desorption study of venlafaxine hydrochloride monohydrate was carried out in a dynamic vapor sorption instrument , available as dvs - 2 from surface measurement systems of london , england . about 30 mg of venlafaxine hydrochloride monohydrate was subjected to a relative humidity - time program at 25 ° c . the sample weight changes were monitored as function of the time and relative humidity . two identical relative humidity - time experiment cycles ( 0 to 90 % relative humidity ) were performed to detect any changes in solid - state properties . the results are shown in fig5 . as shown in fig5 , the venlafaxine hydrochloride monohydrate was stable between 10 and 90 % relative humidity and only lost its hydrate water below 10 % relative humidity . the compound re - hydrates to the monohydrate form when the relative humidity is above 10 %. on cycling , the compound showed two almost identical water sorption / desorption cycles . this is an indication that the solid - state transition of venlafaxine hydrochloride monohydrate was reversible during the dehydration / hydration processes , i . e ., there was no recrystallization of the anhydrate / hydrate phase . xrpd was performed on the venlafaxine hydrochloride monohydrate under both ambient and dry conditions with a scintag x2 x - ray diffraction system model 00 - a02 , available from thermo arl of ecublens , switzerland . the xrpd instrument had the following parameters : scan type : normal start angle : 3 degrees stop angle : 40 degrees number of points : 1851 points step size : 0 . 02 degrees datafile resolution : 1600 scan rate : 0 . 04 scan mode : step wavelength : 1 . 540562 diffraction optics : detector : type : fixed slits x2 configuration : no tube : type : fixed slits x2 configuration : no the results are shown in fig6 . at ambient conditions , the xrpd profile of venlafaxine hydrochloride monohydrate exhibited a highly crystalline phase ( designated “ venlafaxine monohydrate ” in fig6 ). the sample of venlafaxine hydrochloride monohydrate was then subjected to a nitrogen purge ( 0 % relative humidity ) for about 6 hours at room temperature . the xrpd for the sample subjected to the nitrogen purge was different from the original venlafaxine hydrochloride monohydrate sample , indicating the formation of the dehydrated ( anhydrous ) venlafaxine hydrochloride form . see , for example , the new peak at 4 . 367 ° 2θ and small shifts of other major peaks . the intrinsic dissolution rates of the raw material venlafaxine hydrochloride and venlafaxine hydrochloride monohydrate were investigated . pellets of venlafaxine hydrochloride were prepared by compressing 150 mg of each material in a die at 2000 psi for 1 minute with a carver press . the pellets produced were fitted into stainless steel rings and one side of the ring was coated with paraffin wax which resulted in a single exposed surface of the pellet with a surface area of 1 . 327 cm 2 . the dissolution rate in 900 ml of water was determined with the usp method ( usp 23 ( 1995 ), section 711 , page 1791 ) in a dissolution apparatus ( vankel 7000 ) equipped with a cary 300 ultraviolet / isible spectrophotometer , with a rotation speed of 100 rpm at 37 ° c . the distance between the lower end of the stirring element and the bottom of the dissolution vessel was set at 2 . 5 cm . the pellet was centered at the bottom of the flask , and the dissolution media was circulated through a 1 . 0 cm path microflow cell at a flow rate of ˜ 10 ml / minute . absorbance was recorded at 226 nm on a cary 300 spectrophotometer . the results are shown in fig7 . from the slope of the absorbance versus time profile in fig7 , the apparent intrinsic dissolution rates were determined for each sample . because of the high solubility of venlafaxine hydrochloride in water , only two data points are available for calculation . all of the samples had a dissolution rate of 3 . 4 × 10 − 4 g / cm 2 - sec at ph 7 . the present invention is not to be limited in scope by the specific embodiments described herein . indeed , various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and the accompanying figures . such modifications are intended to fall within the scope of the appended claims . it is further to be understood that values are approximate , and are provided for description . patents , patent applications , publications , procedures , and the like are cited throughout this application , the disclosures of which are incorporated herein by reference in their entireties . to the extent that a conflict may exist between the specification and a reference , the language of the disclosure made herein controls .