<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>0008 - Disclosure - INVENTORY</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>From2013-01-01to2013-06-30</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000025743</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2013-06-30T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="6 Months Ended" /><Label Key="Calendar" Id="1" Label="Jun. 30, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>txmd_InventoryAbstract</ElementName><ElementPrefix>txmd_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>InventoryAbstract</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_InventoryDisclosureTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="From2013-01-01to2013-06-30" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="text-indent: 0pt; display: block"&gt;&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: bold 10pt Times New Roman"&gt;&lt;font style="display: inline; text-decoration: underline"&gt;NOTE 3 &amp;#8211; INVENTORY&lt;/font&gt;&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block"&gt;&lt;br /&gt;
&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;Inventory consists of the following:&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-align: center"&gt;
&lt;table cellpadding="0" cellspacing="0" style="width: 90%; font: 10pt times new roman; font-size: 10pt; font-family: times new roman"&gt;
&lt;tr&gt;
&lt;td style="vertical-align: bottom; width: 60%; padding-bottom: 2px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160; &lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 3%; padding-bottom: 2px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td colspan="2" style="vertical-align: bottom; width: 16%; border-bottom: black 2px solid"&gt;
&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: center"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;June 30,&lt;br /&gt;
&lt;/font&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;2013&lt;/font&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left; padding-bottom: 2px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 3%; padding-bottom: 2px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td colspan="2" style="vertical-align: bottom; width: 16%; border-bottom: black 2px solid"&gt;
&lt;div style="text-indent: -9pt; display: block; margin-left: 9pt; margin-right: 0pt; text-align: center"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;December 31,&lt;br /&gt;
2012&lt;/font&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left; padding-bottom: 2px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;/tr&gt;&lt;tr style="background-color: #cceeff"&gt;
&lt;td style="vertical-align: bottom; width: 60%; text-align: left; text-indent: 0pt; padding-left: 0pt; margin-left: 0pt; margin-right: 0pt"&gt;
&lt;div style="text-align: left; text-indent: -9pt; display: block; margin-left: 9pt; margin-right: 0pt"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;Finished product&lt;/font&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;$&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; text-align: right"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;1,100,486&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;$&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; text-align: right"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;1,124,739&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;/tr&gt;&lt;tr style="background-color: white"&gt;
&lt;td style="vertical-align: bottom; width: 60%; text-align: left; text-indent: 0pt; padding-left: 0pt; margin-left: 0pt; margin-right: 0pt"&gt;
&lt;div style="text-align: left; text-indent: -9pt; display: block; margin-left: 9pt; margin-right: 0pt"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;Raw material&lt;/font&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; text-align: right"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;291,035&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; text-align: right"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;380,000&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;/tr&gt;&lt;tr style="background-color: #cceeff"&gt;
&lt;td style="vertical-align: bottom; width: 60%; text-align: left; text-indent: 0pt; padding-left: 0pt; margin-left: 0pt; margin-right: 0pt"&gt;
&lt;div style="text-align: left; text-indent: -9pt; display: block; margin-left: 9pt; margin-right: 0pt"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;Deferred costs&lt;/font&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; text-align: right"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;114,538&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; text-align: right"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;110,471&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;/tr&gt;&lt;tr style="background-color: white"&gt;
&lt;td style="vertical-align: bottom; width: 60%; text-align: left; padding-bottom: 4px; text-indent: 0pt; padding-left: 0pt; margin-left: 9pt; margin-right: 0pt"&gt;
&lt;div style="text-align: left; text-indent: -9pt; display: block; margin-left: 18pt; margin-right: 0pt"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;TOTAL INVENTORY&lt;/font&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%; padding-bottom: 4px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; border-bottom: black 4px double; text-align: left; border-top: black 2px solid"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;$&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; border-bottom: black 4px double; text-align: right; border-top: black 2px solid"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;1,506,059&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left; padding-bottom: 4px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="text-align: right; vertical-align: bottom; width: 3%; padding-bottom: 4px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 1%; border-bottom: black 4px double; text-align: left; border-top: black 2px solid"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;$&lt;/font&gt;&lt;/td&gt;
&lt;td style="vertical-align: bottom; width: 15%; border-bottom: black 4px double; text-align: right; border-top: black 2px solid"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;1,615,210&lt;/font&gt;&lt;/td&gt;
&lt;td nowrap="nowrap" style="vertical-align: bottom; width: 1%; text-align: left; padding-bottom: 4px"&gt;&lt;font style="display: inline; font: 10pt times new roman"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;
&lt;/tr&gt;&lt;/table&gt;
&lt;/div&gt;

&lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for inventory. This may include, but is not limited to, the basis of stating inventory, the method of determining inventory cost, the major classes of inventory, and the nature of the cost elements included in inventory. If inventory is stated above cost, accrued net losses on firm purchase commitments for inventory and losses resulting from valuing inventory at the lower-of-cost-or-market may also be included. For LIFO inventory, may disclose the amount and basis for determining the excess of replacement or current cost over stated LIFO value and the effects of a LIFO quantities liquidation that impacts net income.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section 50

 -Paragraph 1

 -URI http://asc.fasb.org/extlink&amp;oid=6361739&amp;loc=d3e7789-107766



Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section S99

 -Paragraph 1

 -Subparagraph (SX 210.5-02.6)

 -URI http://asc.fasb.org/extlink&amp;oid=6877327&amp;loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

 -Publisher SEC

 -Name Regulation S-X (SX)

 -Number 210

 -Section 02

 -Paragraph 6

 -Subparagraph a, b, c

 -Article 5



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