I agree, you should absolutely not try to CTB with antidepressants, especially new gen: SSRI/SNRI. Tricyclics (first gen) may work, but it's still very bad, practically a NON-METHOD.
if you think about OD, there is only two methods: (im not thinking about OD on chemicals like SN, CO2, inert gas) but like a standard medication you can get in pharmacy/hospital:
- barbiturates (N and others) - which are very hard to get now
- opioids (strong ones, and preferred with benzos) -> you have to take a huge dose to be on the safer side. But it's a good- safe and reliable method (and IMO the only one which you can truly call "OD").
OD's got so bad reputation because ppl try to CTB on wrong substances (like OP proposed) and use wrong dosages / don't use synergy combos/cocktails.
Right now, if you choose to OD, opioid+benzodiazepine is the method to go.