To get this out of the way - unfortunately nearly all of the documentation concerning the US Government's research into the weaponization of pharmaceuticals was destroyed in 1973 when the various programs were officially shut down. What we now know about these programs comes from the report and declassified documents generated by the Senate's 1977 Joint Hearing into MK Ultra, which relied on what little documentation escaped destruction as well as interviews that the Senate conducted with the personnel that were involved.

In 1955 the US Army launched "Material Testing Program EA 1729" which was designed to test the military potential of LSD. Initially these tests were confined to its use as a chemical weapon, with the goal being to create a munition carrying a non-lethal incapacitating agent. This was conducted parallel to the CIA's research, which the Army appears to have initially been unaware of.

Although these tests didn't show any military potential for LSD, they did show a potential for its use in interrogation. This resulted in the Army launching a second phase of the program in 1958 to evaluate LSD's use as an interrogation enhancer.

This second phase involved experimenting on consenting subjects who had been conditioned to resist torture. Essentially, the subjects were told that they were going to be evaluating the potential of polygraphs and sensory deprivation for use in interrogation. The subjects were then secretly administered LSD and then subjected to one of those two methods of interrogation. We don't know much else about this but presumably it showed some positive findings because, unlike the LSD munition, this branch of research was approved for field testing.

That field testing consisted of Projects Third Chance and Dirby Hat. Project Third Chance was carried out in Europe in 1960. Project Dirby Hat was carried out in "East Asia" in 1962. These projects involved using LSD in the interrogation of 17 foreign nationals and 1 US soldier, all of whom were suspected of carrying out intelligence operations on behalf of a foreign power and whom had shown resistance to conventional interrogation.

The results of the interrogations were viewed generally positively, with the Army believing that it got useful information out of the subjects in most cases. However, this information generally came about because of a severely negative reaction to the drugs, which in at least one case required medical intervention to prevent the subject from dying. Essentially, the subjects all followed the same pattern:

1. Immediately after LSD was administered the subject would enter a state of extreme psychosis for several hours during which no useful information could be gathered.

2. The subject would then enter a comatose state for another few hours.

3. The subject would begin to return to normal. As they became more lucid, they would volunteer more and more meaningful information - though this appears to be out of fear of what the Army was doing to them rather than any effect of the drug. (The subjects were unaware that they had been administered LSD, or any drug - so we can only imagine what they thought was happening).

In 1963 the Army's Assistent Chief of Staff for Intelligence was briefed on these results. He appears to have felt that the use of LSD was no different or effective than torture, and ended the Army's program.

By the time that Third Chance and Dirby Hat were carried out the Army appears to have been aware of the CIA's own research into LSD. In fact, the impetus behind Third Chance and Dirby Hat appears to have been that the CIA had not, at that point, conducted any field tests and it was hoped that the Army's field tests would provide a justification for an expanded joint CIA/Army field testing program.

Although the CIA had severely curtailed its research into LSD after the 1953 death of Dr. Frank Olson - a doctor working on MK Ultra who had secretly been administered LSD by other doctors working on the project - it too completely abandoned research into LSD following the Army's 1963 evaluation.

What we know about the CIA's laboratory experiments with other drugs shows that they were generally useless for interrogations. The most success that they had was a method involving barbiturates.

Essentially, the subject would be repeatedly knocked unconscious with a barbiturate. As the subject woke up, they would enter a minimally conscious state during which they would babble. It was possible for interrogators to direct the babbling, and while this would sometimes lead to the subject speaking truthfully it sometimes would not. Most importantly, whether the subject told the truth or not was random enough to be of little use.

So while we know that the Army did use LSD in the field 18 times, due to the destruction of most of the relevant documents in 1973 we will never know for sure whether that was the only time such a pharmaceutical was used. However, it does seem very likely that the Army's use of LSD 18 times was the only use for the following reasons:

1. The main justification for the Army's field use of LSD was the fact that the CIA had, as of that time, not field tested any pharmaceutical to the Army's knowledge; and

2. The only pharmaceutical that the CIA ever identified as having real interrogation potential was LSD, but both the Army and CIA formally abandoned the use of LSD in 1963 when the Army concluded that its use was no different or more effective than conventional torture.

Given the above, it seems unlikely that after 1963 the CIA would have gone back and field tested something other than LSD when they had already determined that every other pharmaceutical was useless in interrogations.