Autism isn't specifically mentioned but you may be able to get a doctor to authorize it but it could still be a problem if you happened to get arrested and charged with illegal cannabis use. If you get the authorization that will cover you for most occurances with a police officer. You never have to divulge why you're authorized for cannabis to a law enforcement official. But if you go to court they will find out why.
The easiest way to get authorized is for pain management. If you have something that hurts tell the doctor you are opiod intolerant and you'll get approved.
Here's the law on the qualifying diseases as they are now. They are getting updated every year or so.
69.51A.010
Definitions.

The definitions in this section apply throughout this chapter unless the context clearly requires otherwise.

(1) "Designated provider" means a person who:

(a) Is eighteen years of age or older;

(b) Has been designated in writing by a patient to serve as a designated provider under this chapter;

(c) Is prohibited from consuming marijuana obtained for the personal, medical use of the patient for whom the individual is acting as designated provider; and

(d) Is the designated provider to only one patient at any one time.

(2) "Health care professional," for purposes of this chapter only, means a physician licensed under chapter 18.71 RCW, a physician assistant licensed under chapter 18.71A RCW, an osteopathic physician licensed under chapter 18.57 RCW, an osteopathic physicians' assistant licensed under chapter 18.57A RCW, a naturopath licensed under chapter 18.36A RCW, or an advanced registered nurse practitioner licensed under chapter 18.79 RCW.

(3) "Medical use of marijuana" means the production, possession, or administration of marijuana, as defined in RCW 69.50.101(q), for the exclusive benefit of a qualifying patient in the treatment of his or her terminal or debilitating illness.

(4) "Qualifying patient" means a person who:

(a) Is a patient of a health care professional;

(b) Has been diagnosed by that health care professional as having a terminal or debilitating medical condition;

(c) Is a resident of the state of Washington at the time of such diagnosis;

(d) Has been advised by that health care professional about the risks and benefits of the medical use of marijuana; and

(e) Has been advised by that health care professional that they may benefit from the medical use of marijuana.

(5) "Tamper-resistant paper" means paper that meets one or more of the following industry-recognized features:

(a) One or more features designed to prevent copying of the paper;

(b) One or more features designed to prevent the erasure or modification of information on the paper; or

(c) One or more features designed to prevent the use of counterfeit valid documentation.

(6) "Terminal or debilitating medical condition" means:

(a) Cancer, human immunodeficiency virus (HIV), multiple sclerosis, epilepsy or other seizure disorder, or spasticity disorders; or

(b) Intractable pain, limited for the purpose of this chapter to mean pain unrelieved by standard medical treatments and medications; or

(c) Glaucoma, either acute or chronic, limited for the purpose of this chapter to mean increased intraocular pressure unrelieved by standard treatments and medications; or

(d) Crohn's disease with debilitating symptoms unrelieved by standard treatments or medications; or

(e) Hepatitis C with debilitating nausea or intractable pain unrelieved by standard treatments or medications; or

(f) Diseases, including anorexia, which result in nausea, vomiting, wasting, appetite loss, cramping, seizures, muscle spasms, or spasticity, when these symptoms are unrelieved by standard treatments or medications; or

(g) Any other medical condition duly approved by the Washington state medical quality assurance commission in consultation with the board of osteopathic medicine and surgery as directed in this chapter.

(7) "Valid documentation" means:

(a) A statement signed and dated by a qualifying patient's health care professional written on tamper-resistant paper, which states that, in the health care professional's professional opinion, the patient may benefit from the medical use of marijuana; and

(b) Proof of identity such as a Washington state driver's license or identicard, as defined in RCW 46.20.035.


[2010 c 284 § 2; 2007 c 371 § 3; 1999 c 2 § 6 (Initiative Measure No. 692, approved November 3, 1998).]

Notes: Intent -- 2007 c 371: See note following RCW 69.51A.005.