Good thing you held off on the methylcobalamin injections - you probably would have had one hell of a reaction.
I have CBS, but not COMT. When I first started, I tried out a moderate amount of hydroxycobalamin, I think like 50mcg? After a few days, I started feeling stressed and anxious. When I retried at lower and lower amounts, the reaction was quicker, like a few hours. I tried methylcobalamin too - same deal. Even 1 mcg was bothering me!
So I got the urine sulfate strips. It tested 1200. I started on a low free thiol diet and gradually added in the supps. The urine sulfate quickly dropped to 800 after a week. I thought it was going to be easy - hah! Then it stayed at 800 FOREVER. Like 3 months. Finally, I got it to 400. Then I retried the B12. I was able to tolerate 0.5mcg (1/2 of one mcg). I've been able to gradually build it up from there to 16mcg per day (divided into 4 doses). That's taken about a month.
You might be different though, and hopefully not as sensitive as me. I've also been taking about 200mcg of methylfolate for a couple of years (technically, not good due to methyl trapping, but it helps with my MCS so I must have enough B12 stores to be making glutathione).
As for COMT, I have a friend who I'm trying to help with COMT. She did Rich's simplified protocol at the full doses for 5 weeks then ran into trouble and had to discontinue. She's not into dividing pills up like I am, so I haven't been able to convince her to try lower doses.
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To specifically answer your questions - if you took out CBS and COMT, yes you could blast away with large amounts of methyl donors, basically a Freddd type protocol or Rich's simplified protocol.
Yes, I would try to get the urine sulfate down to 400.
For COMT, you need a balance, otherwise you'll get mood swings. Yasko's suggestion is to rotate methyl donors. So something like: Monday, B12, Tues folate, Wed TMG, Thurs, B12 and so on. I think hydroxycobalamin is supposed to be the preferred B12 for COMT. You body can make methylB12 and adenosylB12 from that in the ratio it requires. I would keep your amounts below what Rich suggests, or certainly no higher.
I also rely heavily on self muscle testing to determine not only if a substance is good to take, but the amount. I developed my own method for determining amounts. Muscle testing about 95% reliable - really helps guard against bad reactions.