“It’s doing something, all right, but it’s not all it’s cracked up to be,” said Dr. Erick Turner, a former F.D.A. reviewer and an associate professor of psychiatry at Oregon Health & Science University. “I just don’t think it’s going to live up to all the hype.”

Cost is another issue. Janssen is charging the public from $4,720 to $6,785 f or a course of treatment, and clinic costs will add more to the bill, not to mention monthly boosters, if needed. The V.A., not veterans, would foot the bill for whatever price it negotiates with Janssen. But nasal-spray formulations of generic ketamine are already cheaply available from compounding pharmacies, which mix individually tailored doses to order for doctors.

F.D.A. approval requires that people taking Spravato be monitored in a doctor’s office for at least two hours, and their experience entered in a registry. Like ketamine, the drug often causes out-of-body sensations and hallucinations. It is unclear how much of that cost insurers would cover.

The V.A. and the Department of Defense have been trying to reverse an alarming trend of suicide among veterans and members of the military since the late 2000s, when rates began to rise. Suicide rates in the V.A. system have been higher than in the general population for at least a decade, according to Robert Bossarte, an associate professor in the department of behavioral medicine at West Virginia University, in Morgantown. The overall veteran suicide rate decreased recently, from 30.5 per 100,000 in 2015 to to 30.1 per 100,000 in 2016, but longer-term trends are alarming in some groups. In 2015, the suicide rate for male veterans age 18 to 34 rose to 44 in 100,000 per year, from 25 in 100,000 in 2005.

“I’ve tried the generic ketamine nasal spray in about 20 patients with treatment-resistant depression, and a handful of them have done very well on it,” said Dr. William Niederhut, a psychiatrist in private practice in Denver. Dr. Niederhut had the patients take four or five doses over a month, making sure a friend or family member was present, given the disorienting effects. He had the spray made at a local compounder.

The development of Spravato followed a number of small studies over the past decade, which found that doses of the generic anesthetic ketamine could provide fast relief to some severely depressed people who hadn’t responded to other treatments. Generic ketamine has been available for years, at hundreds of clinics around the country; these provide a course of intravenous doses, at $400 to $500 a dose, usually a half dozen over a couple weeks with boosters as needed, for mood problems.

The V.A. is already running its own trials of IV ketamine for severe depression, and the agency could easily have the nasal spray made very cheaply, experts said. Ketamine and esketamine seem to have similar benefits and risks, although careful comparisons have not been done. For depression, esketamine has been studied far more rigorously than generic ketamine.