Sage Therapeutics, Inc.

Exhibit 10.8

Sage Therapeutics, Inc.

September 25, 2011

Albert Robichaud, PhD

3 Riverview Court

Ringoes, NJ 08551

Dear Albert:

Sage Therapeutics, Inc. (the “Company”) is pleased to confirm its offer to employ you as Chief Scientific Officer. As CSO you will be reporting to Kevin Starr (interim CEO).

In the role of CSO, you will

Your effective date of hire as a regular, full-time employee (the “Start Date”) will be Nov 1, 2011. If the Company does not have a health benefits program in place by the time you join and you elect to have health insurance provided by the Company, you will be reimbursed for COBRA (amount to be determined). Once the Company has a health benefits program you will be expected to join the program if you elect to have health benefits provided by the Company.

Your compensation for this position will be at the rate of $300,000 per year, payable monthly in accordance with the Company’s normal pay schedule. All payments are subject to legally required tax withholdings. At this time the Company does not have an annual bonus program in place. It is expected

that, when an annual bonus program is approved by the Board of Directors, the target bonus that you will be eligible for as CSO will be 20% of your annual compensation, based upon achievement of both corporate and personal goals, as agreed to between you and the CEO. You will be eligible to participate each year in any annual bonus plan adopted by the Company, and the Company shall adopt and implement such a plan, if reasonable in light of financial, business and other circumstances and factors.

Sage Therapeutics acknowledges that you currently reside in New Jersey and that you desire to accept this job as essentially a full time position in Massachusetts. As a condition of your employment, you are expected to be on-site at the Company’s offices in Cambridge, Massachusetts for 5 days per week. Since you are choosing not to relocate at this time but instead to commute, the Company will provide you with a one-time Commuting Assistance Payment in the form of a sign-on bonus of $115,000 which will be paid to you in two installments. You will receive the first payment of $65,000 during your first month of employment and it will be subject to customary deductions and withholdings as required by law. You will receive the second payment of $50,000 upon the first anniversary of your Start Date with Sage. Should you voluntarily leave the Company, other than for death or disability, within 6 months of receiving either payment, you will be obligated to return the gross amount of the payment to the company within 30 Days of your departure date.

Subject to the approval of the Board of Directors of the Company (the “Board”), in connection with the commencement of your employment, the Board will grant you an option to purchase 700,000 shares of the Company’s common stock (the “Option”). The Option will be granted following the commencement of your employment. The exercise price of the Option will be at least equal to the fair market value of the Company’s common stock on the date of grant, and the Board of Directors may elect to seek a third party valuation of such fair market value, which could delay the date that the Option is granted. The Option will be subject to the terms and conditions of the Company’s then-current stock option plan and form of stock option agreement. These options will vest as follows: one quarter of the shares will vest on the first anniversary of the Start Date, and following that, 1/48^th of the shares will vest on a monthly basis, in arrears. Vesting is contingent on your continued full-time employment with the Company.

It is understood that you are an “at-will” employee. You are not being offered employment for a definite period of time, and either you or the Company may terminate the employment relationship at any time and for any reason, with or without cause or prior notice and without additional compensation to you.

The Company may terminate your employment at any time upon written notice to you. In the event that the Company terminates your employment for any reason (other than Cause (as defined below)), then, subject to the condition precedent of your execution and delivery of a standard form general release of the Company to be delivered to you at the time of your termination, you will be entitled to a severance payment in an aggregate amount equal to six-months of your then base salary as of the date of termination, such amount to be paid in equal installments over a six (6) month period after the date of your termination in accordance with the Company’s usual payroll practices and periods, subject to applicable taxes and withholding.

For purposes of this letter agreement, “Cause” means (i) your material breach of this letter agreement or any other agreement between the Company and you (including the NDA and Non-Competition Agreement (as defined below), (ii) your material failure to adhere to any policy of the Company generally applicable to employees of the Company, (iii) your appropriation (or attempted appropriation) of a business opportunity of the Company, including attempting to secure or securing any

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personal profit in connection with any transaction entered into on behalf of the Company, (iv) your misappropriation (or attempted misappropriation) of any of the Company’s funds or property, (v) your conviction of, or the entering of a guilty plea or plea of no contest with respect to, a felony, the equivalent thereof, or of a lesser crime having as its predicate element fraud, dishonesty or misappropriation, (vi) your willful misconduct or your continued and willful failure or refusal to perform any material duties reasonably requested by the executive of the Company to whom you report, the Chief Executive Officer of the Company or the board of directors, (vii) your engaging in bad faith or gross negligence in the performance of your duties for the Company, (viii) other behavior that is materially injurious to the Company (whether from a monetary perspective or otherwise), and (ix) your intentional commission of an act constituting fraud, embezzlement, breach of any fiduciary duty owed to the Company or its stockholders or other material dishonesty with respect to the Company, in each case as determined in good faith by the board of directors of the Company; provided, however, that in the case of conduct described in clauses (i) and (ii) hereof, such conduct shall not constitute “Cause” unless (a) the Company shall have given you written notice setting forth with specificity (i) the conduct deemed to constitute “Cause,” (ii) reasonable action that would remedy the objectionable conduct, and (iii) a reasonable time (not less than ten (10) business days) within which you may taken such remedial action, and (b) you shall not have taken such specified remedial action within such specified reasonable time.

Your normal place of work will be Cambridge, MA (location to be determined at a later date). Enclosed for your review is a “Non-Solicitation, Confidentiality and Assignment Agreement” (the “Agreement”).

This offer of employment is conditioned on your willingness to sign and abide by the terms of the Agreement. You will be expected to sign the Agreement before you report for work.

In making this offer, the Company understands, and in accepting it you represent that you are not under any obligation to any former employer or any person or entity which would prevent, limit, or impair in any way the performance by you of your duties as an employee of the Company.

The Immigration Reform and Control Act requires employers to verify the employment eligibility and identity of new employees. You will be required to complete a Form 1-9 which will be provided to you before the Start Date. Please bring the appropriate documents listed on that form with you when you report for work. We will not be able to employ you if you fail to comply with this requirement. Also, this offer is subject to satisfactory reference checks if necessary.

This letter agreement and the Agreement referenced above constitute the complete agreement between you and the Company, contain all of the terms of your employment with the Company and supersede any prior agreements, representations or understandings (whether written, oral or implied) between you and the Company. This letter agreement may not be amended or modified, except by an express written agreement signed by both you and a duly authorized officer of the Company, although your job duties, title, reporting relationship, compensation and benefits may change from time to time, at the Company’s option.

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Please indicate your acceptance of this offer by signing and returning the enclosed copy of this letter no later than 5pm ET on September 27rd, 2011.

You may sign, scan, and email the letter to ***@***. We look forward to your joining the Company and are pleased that you will be working with us.

Very truly yours,

Kevin Starr

President & Chief Executive Officer

Sage Therapeutics, Inc.

Accepted and Agreed:

Albert Robichaud

10/4/2011

Date

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