Ok. My health is crap, and I will be honest, I tend to hope people will research things a bit before coming to conclusions. If I can manage to get myself to sit up and do the searches I will post all the links that are easily found by anyone for you. There IS data easily found showing that without intervention or vomiting 6gr from a 100ml bottle has almost, if not, a 100% success rate.
Found the first one before I even sat up.
"Is one 100ml bottle of Nembutal enough for a peaceful death?
While there are several florid accounts of failure by people taking a full
100ml bottle of veterinary Nembutal, closer scrutiny shows a much more
complex situation. Exit has examined the details and medical records of
several such cases.
In the vast majority of cases, one bottle (100ml @ 60mg/ml) of Nembutal
will be satisfactory. However, there is a small group (<1%) who may exhibit
a prolongued comatose phase before death (sometimes up to 24 hours).
Outright 'failures' remain extremely rare. Indeed, all of the reported failures
investigated were associated with discovery and medical intervention. This
emphasises the need for careful selection of the place chosen to take the
drugs.
In some of the analysed cases, the long comatose phase is associated with the
prolonged use of anti-psychotic medication, prior to taking the barbiturate.
It is presumed the induction of liver enzymes by these drugs causes some
degradation of the Nembutal before it reaches the brain. In this situation,
increasing the quantity of drug taken (eg. to 2 bottles, 12gm) may not
necessarily hasten the death.
Exit has examined the use of several potentiating drugs which may be
dissolved into the liquid Nembutal, removing any possibility of extended
coma. The results of these tests will be published in future editions of the
eHandbook."