Montana's list of qualifying conditions is a bit more restrictive than other states:
Cancer
glaucoma
positive status for HIV/AIDS
cachexia or wasting syndrome
intractable nausea or vomiting
epilepsy or an intractable seizure disorder
multiple sclerosis
Crohn's disease
painful peripheral neuropathy
a central nervous system disorder resulting in chronic, painful spasticity or muscle spasms
admittance into hospice care, or any other medical condition or treatment for a medical condition approved by the legislature.
Severe chronic pain is also included, and requires either proof in the form of lab tests or imaging, or a second opinion by another physician.
Post-traumatic stress disorder was added in the 2016 voter initiative, I-182.