The high court ruled this month that the practice known as "psychiatric boarding" was unlawful. The state estimates that the ruling applies to about 200 people.
Complying with the court's decision will cost the state "tens of millions of dollars in the short term," said Andi Smith, Gov. Jay Inslee's senior policy adviser on health and human services, during a call with reporters Thursday.
She said that the state plans to add 50 beds by Aug. 27, leaving the potential for some people to be released without care.
Inslee hasn't ruled out a special session, Smith said, but the Department of Social and Health Services may be able to shift resources until a supplemental budget request is made to lawmakers next year.
Mental-health officials have been struggling to respond to the high court's Aug. 7 decision.
The justices ruled that mentally ill patients who are involuntarily committed cannot be "warehoused" in emergency rooms or acute care centers as a way to avoid overcrowding certified mental health facilities. Patients have a right to adequate care and individualized treatment, and state law required they be detained in certified evaluation and treatment facilities, the court said.
"We simply don't have the bed capacity to serve all the people who need treatment," Smith said, adding that they're working hard but "the problem will not be solved on Day 1."
The state's involuntary treatment law passed in 1973 allows people to be committed to a mental hospital or institution against their will for a limited period of time. The purpose is to evaluate and treat people with a mental disorder who may be gravely disabled or pose a danger to themselves.
The state has been using "single bed certifications" as a way to temporarily hold involuntarily committed people in hospitals that aren't certified to evaluate or treat their mental illness.
In response to the court decision, state health administrators are planning to add 50 beds, including a few beds at Eastern State Hospital at Medical Lake, as well as at two psychiatric hospitals in King County and community-based facilities, said Jane Beyer, with the Social and Human Services agency.
It's unclear what will happen to patients who won't have psychiatric beds after the court decision kicks in this month.
Hospitals have a mandate to safety discharge plans, and they may still take in mentally ill people and provide care for them even though the single-bed certifications will be unlawful, Smith said.
The state is also hoping that plaintiffs who brought the case against Social and Health Services won't ask to eliminate hospitals' ability to hold mentally ill people at emergency rooms for 72 hours, Beyer said.