A number of different fiber supplements show evidence of benefit for constipation, with psyllium being perhaps the most well-established in this regard.[1]
Probiotics (taken via capsules or fermented foods) have sometimes been found to improve symptoms of constipation.[2][3] More research is needed to determine which probiotic strains are effective, although Bifidobacterium lactis specifically appears beneficial.
Senna, an herb sometimes taken in the form of tea, has a well-established laxative effect. Cascara (Frangula purshiana) bark is another herb often taken for its laxative properties; it contains the same active chemicals (anthraquinones) as senna.
Magnesium — usually in the form of magnesium oxide or magnesium citrate — can also act as a laxative when taken in high enough amounts. However, it is important to speak to your healthcare provider before taking magnesium, as the high doses often used for constipation can lead to a harmful elevation of blood magnesium levels, especially in people with impaired kidney function.[4]