THIRD SUPPLEMENTAL INDENTURE

Exhibit 4.2

THIRD SUPPLEMENTAL INDENTURE

THIS THIRD SUPPLEMENTAL INDENTURE dated as of October 24, 2006 among CRC Health Corporation, a Delaware corporation (the “Company”), the Guarantors, Madrid Merger Corporation, a California corporation (the “New Guarantor”) and U.S. Bank National Association, as trustee (the “Trustee”).

WHEREAS, the Company and the Guarantors have heretofore executed and delivered to the Trustee an indenture dated as of February 6, 2006 (the “Indenture”), providing for the issuance of $200 million aggregate principal amount of the Company’s 10.75% Senior Subordinated Notes due 2016 (the “Notes”), as supplemented by the First Supplemental Indenture, dated as of July 7, 2006 (the “First Supplemental Indenture”) and further supplemented by the Second Supplemental Indenture, dated as of September 28, 2006 (the “Second Supplemental Indenture”);

WHEREAS, the Company and the Guarantors propose to further amend and supplement the Indenture to join the New Guarantor, an indirect subsidiary of the Company, as a party to the Indenture as a Guarantor thereunder;

WHEREAS, pursuant to Section 8.01 of the Indenture, the Company and the Trustee may amend, waive or supplement the Indenture, the Notes or the Guarantees without the consent of any Holders to make any change that would provide additional rights or benefits to the holders of Notes or that does not adversely affect the legal rights under the Indenture of any such holder;

WHEREAS, the Company, each Guarantor and the New Guarantor have been authorized by their respective board of directors, partners, or general partners, as applicable, to enter into this Third Supplemental Indenture;

WHEREAS, all other acts and proceedings required by law, by the Indenture and by the respective certificates of incorporation, certificates of formation, partnership agreements, limited partnership agreements, by-laws and other organizational documents of the Company, each Guarantor and the New Guarantor to make this Third Supplemental Indenture a valid and binding agreement for the purposes expressed herein, in accordance with its terms, have been duly performed;

WHEREAS, pursuant to Section 8.06 of the Indenture, the Trustee is authorized to execute and deliver this Third Supplemental Indenture;

WHEREAS, the Company hereby requests that the Trustee execute and deliver this Third Supplemental Indenture;

NOW, THEREFORE, for in consideration of the premises herein contained and in order to effect the proposed amendment to join the New Guarantor to the Indenture pursuant to Section 8.01 of the Indenture, the Company, the New Guarantor and the Guarantors agree with the Trustee as follows:

ARTICLE I

Amendment of Indenture

1.1. Amendment of Indenture. As of the date hereof, this Third Supplemental Indenture amends the Indenture by joining the New Guarantor as a party to the Indenture, as a Guarantor thereunder.

1.2. Execution and Delivery of Note Guarantee. Upon the effectiveness of this Third Supplemental Indenture, the New Guarantor agrees that a notation of its Guarantee substantially in the form attached as Exhibit G to the Indenture, will be endorsed by a duly authorized officer of the New Guarantor on each Note authenticated and delivered by the Trustee under the Indenture.

ARTICLE II

Miscellaneous Provisions

2.1. Instruments to be Read Together. This Third Supplemental Indenture is an indenture supplemental to and in implementation of the Indenture, and said Indenture, the First Supplemental Indenture, the Second Supplemental Indenture and this Third Supplemental Indenture shall henceforth be read together.

2.2. Confirmation. The Indenture as amended and supplemented by the First Supplemental Indenture, the Second Supplemental Indenture and further amended and supplemented by this Third Supplemental Indenture is in all respects confirmed and preserved.

2.3. Terms Defined. Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

2.4. Counterparts. This Third Supplemental Indenture may be signed in any number of counterparts each of which so executed shall be deemed to be an original, but all such counterparts shall together constitute but one and the same instrument.

2.5. Effect of Headings. The section headings herein are for convenience only and shall not affect the construction hereof.

2.6. Effectiveness. The provisions of this Third Supplemental Indenture will take effect immediately upon execution thereof by the parties hereto.

2.7. Trust Indenture Act Controls. If any provision of this Third Supplemental Indenture limits, qualifies or conflicts with another provision that is required by or deemed to be included in this Third Supplemental Indenture by the Trust Indenture Act, the required or incorporated provision shall control.

2.8. Governing Law. THIS THIRD SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE

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STATE OF NEW YORK, AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK.

2.9. Trustee. The Trustee makes no representations as to the validity or sufficiency of this Third Supplemental Indenture. The recitals and statements herein are deemed to be those of the Company, the Guarantors and the New Guarantor and not of the Trustee.

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IN WITNESS WHEREOF, the undersigned have executed this Third Supplemental Indenture this 24th day of October, 2006.

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