Source? I don’t think Sagan suggested the LSD use either way, that was John Lilly’s thing.
Sagan was interested in Lilly’s dolphin experiments because he was interested in developing inter species communication techniques, because he was really interested in how we could communicate with aliens.
Lilly was the psychonaut. He invented the sensory deprivation tank during the dolphin experiments, would use it on LSD to try to telepathically communicate with them, and gave the dolphins LSD a few times. Years after the dolphin experiments he went kind of nuts taking high dose ketamine and trying to communicate with aliens.