Literature and websites most commonly cite Seconal (Secobarbital) and Nembutal (Pentobarbital) as the two most effective barbiturates for a swift, painless and swift death. The suicide holy grail. Seconal is a strong sedative that is used to treat severe, long-standing insomnia in people already taking barbiturates. Reportedly this drug is not even available on prescription in the UK anymore, although it may well be in other countries, including the USA.