drug transportation rates through the skin are generally low , but therapeutic plasma levels can be achieved for drugs with suitable properties . that is , the drug should be highly potent , the daily dose requirement should be low , and therapeutic plasma levels should be ˜ 10 nanograms / ml . plasma levels for therapeutic effects of thc are in the range of 10 nanograms / ml , making thc a suitable candidate for transdermal administration . the source of thc and related compounds used are usually crude extracts of marijuana plants , the purified form of the drug being obtained by supercritical fluid extraction ( scfe ) of the crude extracts or other suitable extraction methods . however , synthetic forms may be utilized . solubility of the active ingredient thc in the carrier is a very important consideration when preparing the pharmaceutical composition of the present invention , and should be assessed before making any transdermal delivery . thus , solubility of thc alone was determined by the present inventors in a 70 : 30 water : alcohol ( v / v ) mixture , a 50 : 50 water : alcohol ( v / v ) mixture , as well in 30 : 70 water : alcohol ( v / v ) mixtures containing various permeation enhancers . the solubility tests for each of the samples was performed as follows : approximately 50 - 60 mg of thc was placed into each of six different centrifuge tubes . in each of these centrifuge tubes , 1 ml of ethanol : water solution ( 70 : 30 v / v ) and 5 % v / v ( volume solute per volume of solvent ) of permeation enhancer ( caproic acid , caprylic acid , tween 80 , lauric acid and oleic acid , for each of test samples 3 - 7 , respectively ) was added thereto . the centrifuge tubes were then mechanically agitated at room temperature for 24 hours . the samples were then centrifuged at 3500 rpm for 5 minutes and filtered through a 0 . 2μ whatman filter . the filtrate was diluted and analyzed by hplc . the solubility of thc in test samples 1 - 7 is given in table i below . as shown above , test sample # 1 was dissolved in a 50 : 50 ethanol : water solution , but after centrifugation and filtration , the concentrated solution was hazy . after analyzation , solubility in such a solution without permeation enhancer and a high concentration of water was found to be very low ( 2 . 86 mg / ml ). when the solvent system was changed to 70 : 30 ( ethanol : water ) solubility of thc was increased appreciably ( 20 . 21mg / ml ). however , it was found that the solubility of thc could be dramatically increased ( almost doubled ) be including either of two permeation enhancers , caprylic acid or lauric acid , in the thc containing solution . the pharmaceutical composition of the present invention may be formed into a gel or powder composition for transdermal / transcutaneous application . the methods of manufacturing such variations of the pharmaceutical composition are shown below . however , the methods of manufacturing said composition should not be limited solely to the examples below . polymethacrylic acid ( pma 100 , 000 ) and polyethylene glycol ( peg - 8000 ) were dissolved in ethanol in two different beakers utilizing a stirring waterbath ( 40 - 45 ° c .). the ratio of polymethacrylic acid to polyethylene glycol ( pma : peg ) was 2 : 1 . both the solutions were mixed until they formed a clear solution . the solutions were then cooled to room temperature . water was then added to each of the two solutions in increments of 1 g , and at the addition of 10 g , the solution formed a whitish gel . the gel was collected and dried in an oven . the dried mass ( pma - peg complex ) was then ground to powder . a powder complex was prepared with peg - 20000 , but the agglomerate was so hard that it was difficult to grind to powder . therefore , peg - 8000 was used for making the complex to get a free flowing powder . a 10 % solution was made by dissolving the pma - peg complex made above in a 65 : 35 acetone : ethanol mixture using continuous stirring . the resulting solution formed a viscous solution . thc ( tetrahydrocannabinol ) solution was then prepared by dissolving thc in ethanol . this thc solution was then added to the pma - peg complex solution produce above , as well as with a permeation enhancer . initially , two formulations ( formulations 1 & amp ; 2 ) were prepared ( containing 25 mg / ml and 14 . 6 mg / ml of thc each , respectively ) and analyzed to determine the percent recovery . later six formulations ( formulations 3 to 8 ) were prepared containing differing amounts of thc alone and in combination with permeation enhancers . another pma of low molecular weight 15000 was also used forming a complex with peg - 8000 . six more formulations ( formulations 9 to 14 ) were prepared using the complex powder and permeation enhancer . for these six formulations 9 - 14 , the ratio of the solvent system of acetone : ethanol : water was 65 : 25 : 10 , respectively . a powder complex could not be prepared by using polyacrylic acid ( paa 450 , 000 ) and peg 8000 because a gel was instantly formed and , after drying , the gel formed a plastic - like mass which was difficult to grind . all of the above formulations 1 - 14 were then analyzed by hplc . the results of the hplc analysis are shown below in table ii . the following gel and film formulations were prepared with pma ( 100000 ) and peg ( 8000 ). 1 . 26 g of polymethacrylic acid ( pma 100 , 000 ) was dissolved in a 75 % v / v alcohol : 25 % v / v water mixture using continuous stirring at 45 - 50c . after 2 hours of continuous stirring , a viscous solution was formed . then , about 2 . 0 g of peg - 8000 was dissolved in alcohol with continuous stirring in a water bath at a temperature 45 - 50 ° c .). both the pma and peg solutions were mixed until they formed a clear solution . the clear solution was kept at room temperature . the pma : peg ratio was 1 . 25 : 2 . 74 mg of thc was then dissolved in 1 ml of alcohol , and the resulting thc solution was then poured into the viscous pma : pga complex solution , and continuously stirred . a clear gel was formed ( formulation - 16 ). five more formulations ( formulations 17 to 21 ) were then prepared in the same method . however , a 5 wt % of permeation enhancer was added to each of formulations 17 - 21 . five more formulations ( formulation 28 to 32 ) were prepared using a solution having a pma : peg ratio of 2 : 1 . all these formulations were then subjected to hplc analysis to determine the percent recovery and physical appearance of the gel formulation , the results of these hplc tests being shown in table iii below : gel formulations were prepared with polymethacrylic acid ( pma 15000 ) and polyacrylic acid ( 60000 ). both of these compounds are commercially available as a sodium salt solution . however , formulations containing these compounds failed to form a gel after mixing with peg - 8000 solution . polyacrylic acid ( 450 , 000 ) formed a gel with peg - 8000 . but , it was an opaque gel , and not used since all the gel formulations should preferably be transparent . initially , two placebo gel formulations # 1 and # 2 , for use in vivo testing , were prepared using two different concentrations of carbopol as follows : however , placebo gel formulation # 1 formed a turbid solution rather than a gel . formulation # 2 did form a gel . five more formulations 33 - 37 were then prepared by adding carbomer to about 8 . 8 g of propylene glycol , the solution then being continuously stirred in a container overnight . once the carbomer went into solution , permeation enhancer and thc were dissolved in 0 . 5 ml alcohol , and the thc solution then mixed well with carbomer solution and stirred for 15 minutes . the resulting gel formulations 33 - 37 were then analyzed by hplc to determine the percent recovery ( the amount of thc remaining in the gel formulation after preparation thereof ). the results of these hplc tests are shown below in table iv . five more gel formulations 38 - 42 were prepared according to the above method , and in addition , adding polymethacrylic acid to the solution . all the formulations were desirably transparent . gel formulations 38 - 42 were then subjected to hplc analysis to determine percent recovery , the results of these tests being shown in table v below : about 1 . 0 g of pma ( 100 , 000 ) was dispersed in 7 . 5 ml of alcohol and 2 . 5 ml of water , the resulting mixture then being continuously stirred for about 2 hours . once the pma went into solution , about 1 . 0 g of peg 8000 was dissolved in 2 ml of alcohol , and this peg solution was added to the pma solution and continuously stirred overnight . after overnight stirring , a clear , viscous solution was obtained . five pma - peg complex solutions were prepared according to the method above , and 5 % w / w permeation enhancer was added to the solution . thc was then dissolved in 1 ml of alcohol , the resulting thc solution was added to the pma - peg complex solution , and the mixture was continuously stirred for 20 minutes to form formulations 23 - 27 . each of formulations 23 - 27 were then individually spread on a petri dish covered with para - film and dried in a drying oven at a temperature below 35 ° c . to form a film formulation . the prepared films were translucent , and the thickness thereof varied from 0 . 25 mm to 0 . 45 mm . a fixed area of film for each formulation 23 - 27 was then cut and subjected to hplc analysis , the results of the hplc analysis being shown in table vi below : each of the film formulations 23 to 27 shown above were used for in vitro skin permeation studies . permeation experiments were assessed using a franz diffusion assembly . both rat and human skin were used for the study . initially , full thickness normal rat skin was used . hairs were removed from the skin using a clipper . before mounting into the diffusion cell , the subcutaneous fat layer was separated from the skin . it was cut according to the size of the donor cell , with a surface area of 0 . 64 cm 2 . the skin was mounted in between the donor and receiver compartment . the receiver compartment contained a 50 % hydro - alcoholic ( water : ethanol ) solution for ensuring the pseudo - sink conditions by increasing the solubility of thc in the medium . temperature was maintained at 37 ° c . two formulations , formulations 3 and 4 , were tested to determine the permeation ability of the formulations into skin . formulation 3 contained 8 . 6 mg / ml of thc , and formulation 4 contained 9 . 86 mg / ml of thc . the donor compartment contained 0 . 5ml of the formulation , and the receiver compartment contained 5 . 1 ml of the hydro - alcoholic solutions . two hundred microliters ( 200 μl ) of sample was withdrawn and replaced with fresh amount of fluid . samples were withdrawn from the tested skin at 0 , 1 , 2 , 3 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 42 , 43 , 44 , 45 , 46 , 47 , and 48 hours . the results of the permeations tests are shown graphically herein in fig2 and 3 . samples were then analyzed by hplc . the results of the hplc analysis for formulation 3 is shown in table vii below , and the results of the hplc analysis of formulation 4 is shown in table viii below : further , in vitro skin permeation studies were conducted using formulation # 43 , a transdermal gel , which was prepared as follows : pemulen was first dissolved in a mixture of ethanol and water , triethanolamine was added thereto , and the resultant mixture was mixed well to firm a first pemulen solution . tetrahydrocannabinol ( thc ) was then dissolved in a portion of alcohol , and isopropylmyristate was then added thereto , to form a second thc solution . both the first pemulen solution and the second thc solution were mixed for 30 minutes , and a transparent gel was subsequently formed . this gel had a ph of 6 . 0 . there were no gritty particles . an irritation study was conducted for the formulation on a rat , the results of this study indicating that the formulation did not induce any redness associated with erythema when applied transdermlly . the formulation # 43 had the following formula : permeation experiments on rat skin were performed for formulation 43 , as described above for formulations 3 and 4 . the results of these permeation experiments are shown below in table ix . the data presented above in table ix was then graphed to illustrate the permeation of thc into the skin over time . this graph is shown in fig4 herein . thus , after extensive experimentation , the present inventors discovered that transdermal thc administration overcomes the problem of variation in absorption and metabolism associated with oral administration . further , it was unexpectedly discovered that transdermal administration increases bioavailability and the efficacy of thc by avoiding the liver first - pass inactivation , which significantly lowers the plasma , and brain concentration , of thc administered orally . therefore , small doses of thc can be administered to a patient , resulting in fewer side effects , and the drug is more tolerable and more effective in treating patients . additionally , as thc is heavily metabolized by the liver , transdermal / transcutaneous administration of thc , as opposed to oral administration , may help to reduce drug - drug interactions with the other drugs that are also extensively metabolized by the liver . the in vitro skin permeation data shown in fig2 - 4 suggests that zero order kinetics were followed from all formulations , and that 10 . 8 g / sq . cm ./ hr transdermal gel delivery is feasible to achieve the desired systemic effect . a steady state flux of 8 . 8 g / sq . cm ./ hr was estimated based on the total clearance and minimum effective concentration . the pharmaceutical composition of the present invention is useful , but not limited to , treating pain , nausea , vomiting ( particularly that associated with chemotherapy in cancer patients ), glaucoma , arthritis , dementia , multiple sclerosis , and for deterring weight loss in aids patients .