Good advice trainspotter. A good fiber to use is something more soluble like Citrucel or benefiber. The total fiber intake should be a goal of 28-30 grams per day, which should be gradually achieved.
Miralax is good, but many find it to be "messy" and I actually had one doctor term the result of it "all gush and no push". I hated it.
I found that if you take fiber with it, it works better.
Also, Senna is fine and sorry to contradict you but the research has shown it not be tolerance forming,
Although long-term laxative therapy has traditionally been considered contraindicated and a risk factor for colonic denervation and reduced motility , current data suggest that the colonic dysfunction sometimes attributed to long-term laxative use (“ cathartic colon ”) may actually be the reason for long-term laxative therapy as opposed to the result.
Doughty, Dorothy B. (2012-10-12). Urinary & Fecal Incontinence: Current Management Concepts (Urinary and Fecal Incontinence) (Kindle Locations 18064-18067). Elsevier Health Sciences. Kindle Edition.
At my job, we generally recommend Senna-S for opiod related constipation. We titrate the dose upward as needed.
Another natural option is the following formulas:
Bran formula
1 cup unprocessed miller's bran
1 cup applesauce
1/4 cup prune juice
take 1 tablespoon per day initially; increase the daily dose by 1 tbsp each week until desired results are obtained
Power Pudding
1/2 cup prune juice
1/2 cup applesauce
1/2 cup wheat bran flakes
1/2 cup canned or stewed prunes
1/4 cup day initially; increase the daily dose by 1/4 cup each week until desired results are obtained.
If you find yourself in a real jam
First try a glycerin suppository, if that doesn't work, use a dulcolax
If that doesn't work Get a mineral oil enema. This stays in the colon for quite a while and softens the stool. You are supposed to follow up with a fleets enema, but often the mineral oil enema is enough.
Hopefully you will never need to go beyond this, but there have been instances where a milk and molasses enema have had to be used.
Other laxatives work well for other people but these are pretty tried and true