At my clinic 120mg is the newest maximum allowed methadone dose in Ontario, CA...you can increase it further but its a bit of a hassle, take blood before & 4hrs after your dose - to check the metabolism rate, various other medical tests - ECG for sure maybe being the least intrusive & you need to have the recommendation of 2 doctors saying that you need a higher dose. Someone from the clinic once told me that when he was on 400mg (not a typo) he truly didn't have any cravings but he was useless as far as normal activities go, could barely getting up to answer the door. I also met someone younger to my age who was on 600mg/day.
When I first when on MMT in 2004 they would let you increase as much as you wanted and I went up to 205mg/day, along with 6x carries per week that's 1.25g methadone a week. Insane looking back on it.
To the O.P. I have met several people at the clinic who were on high doses of methadone anywhere from 100mg-130mg, whom were basically abusing their methadone, taking double or triple doses then laying in bed sick as dogs for the next few days or in search of more methadone (only thing that works at that dose, 100mg+). They decided to switch to suboxone and the general understanding is you need some time, a few months, to taper your methadone dose down to 40mg-30mg and/or make you go 36hrs-48hrs more or less, until you are in withdraws and *then* you are supposed to take 2mg suboxone every 30min or every 1hr until you reach your dose, at the clinic that where nurses/doctors are nearby - at least that's the original version.
On the other hand there have been cases in 3 people I know whom were on large methadone doses, over 100mg but under 140mg! In all cases they decreased from they're respective doses down to 40mg methadone and were given the suboxone at that dose. The decrease in methadone was very acute, short as in under 2 weeks even 1 week taper from 100mg+ to 40mg.
If you have a strong will, if not grab some benzos you can easily go from methadone to suboxone, opiates do not cause seizure even if you feel like you are going to die there are no life threatening effects from withdraw as opposed to benzos which do cause seizure and life threatening effects, not saying it will be easy though!
