It's a TCA so it's going to have similar effects to
other tricyclics in overdose. It can work alone but it may take a long time and might result in unpleasant symptoms like nausea, vomiting, headache, rapid heart rate and convulsions.
The
PPeH recommends using it on combination with other medications to make it more peaceful and certain, but those can be hard to obtain (morphine, digoxin, diazepam).
Search the forum for DDMA to find more information on the suggested combinations.