During my last cycle I had a revelation: I realized that although O2 does abort my CH attacks, breathing it through both my nostrils is less effective. Once I blocked my right nostril (on the side of the pain) with a tissue, the time until the attacks stopped dropped down from 10-15 minutes to 4-8 minutes.

I recently went to a conference about updated treatments for CH. One of the things they talked about was treating CCH with medical cannabis, which seems to be very effective for some but also triggers attacks for many.

Personally, I had mixed results with cannabis in the past, but the lecture has motivated me to try again - this time with a tissue up my right nostril, like with the O2. To my surprise, this simple change helped me stop shadows and even abort one attack.

I speculate that the triggering effect smoking cannabis has on some people is connected to the irritation to the inside of the nose, not to the cannabinoids entering the body. Which may also explain why smoking a cigarette during the onset of an attack may make it much worse, but CHers who quit smoking usually see little improvement in terms of frequency or intensity.

I suspect blocking the nostril might make other abortive treatments more efficient and may even serve in some cases as a preventive measure, especially when an attack starts.