Having suffered with a fissure for at least three months, I decided to cut out all caffeine after reading about the potential for caffeine to increase muscle tension. I had previously noticed this effect in my own muscles, and my struggle with the fissure led me to wonder if this increase in involuntary contractions could be hindering my healing by preventing blood flow to the area.
It was difficult cutting out coffee and tea because I've basically become dependent on them over the years, but I would give up just about anything to avoid that particular pain. So, after two weeks without caffeine, I can say that I've noticed enough improvement in my condition to continue the experiment.
In addition to going no-caffeine, I've added magnesium glycinate and magnesium malate to my morning and nighttime regimen to support muscle relaxation. The improvement I'm experiencing, aside from diminished pain, is a feeling of generally lower muscle tension, particularly in the crucial sphincter zone. I have a rather high-stress life, and it seems that my morning coffee was enough to initiate a daily cycle of subtle but significant muscle spasms. If you are struggling to make progress with a chronic fissure and catch yourself tensing the muscles down there, I'd recommend going caffeine free for a month to see if it makes a difference.
Hope this helps someone!