Serious allergic reactions including anaphylaxis, difficulty breathing/wheezing, skin rash, and hives have been reported after ingestion of psyllium products. Less severe hypersensitivity reactions have also been noted. Cross-sensitivity may occur in people with allergy to English plantain pollen (Plantago lanceolata), grass pollen, or melon.

Psyllium-containing laxatives, cereals, and other products are generally believed to be safe. Important exceptions include those with repeated psyllium exposure (such as healthcare workers frequently handling bulk laxatives who are at risk for hypersensitivity reactions) and patients with significant pre-existing bowel abnormalities (such as gastrointestinal strictures or impaired motility) or prior bowel surgery.

Obstruction of the gastrointestinal tract has been noted in numerous case reports of patients taking psyllium-containing laxatives, particularly in individuals with previous bowel surgery or problems and/or when the laxatives are mixed with inadequate amounts of water. Psyllium should be avoided by people who have throat problems or difficulty swallowing.

Gastrointestinal side effects are generally mild and have not prompted discontinuation of psyllium in most clinical trials. Esophageal obstruction has been reported in a patient with Parkinson's disease.

Due to potential reductions in blood sugar levels caused by psyllium, blood glucose levels in diabetic patients should be closely monitored.

Immediate medical attention should be sought if any of these symptoms appear after taking psyllium: chest pain, vomiting, or difficulty swallowing or breathing.

Psyllium-containing laxatives are considered class C-2 drugs in pregnancy, meaning that they appear to be safe in all three trimesters, although studies in pregnant humans and animals have not been done. Psyllium-containing products are considered class 1 (apparently safe) during breastfeeding.

Recommendations for dietary fiber intake for adults fall within the range of 20 to 35 grams per day, or 10 to 13 grams per 1,000 kilocalories ingested.

It is important to take laxatives such as psyllium with sufficient amounts of water or liquid in order to reduce the risk of bowel obstruction. Doses ranging from 2.2 to 45 grams by mouth daily in divided doses, often administered just prior to meals, have been used in studies.

3.4 to 16 grams by mouth daily has been studied, although more research is needed to establish benefits and long-term safety.

Psyllium-containing products may delay gastric emptying time and reduce the absorption of some drugs. It is advised that drugs be taken at separate administration times from psyllium to minimize potential interactions (for example, one hour before or a few hours after taking psyllium).

Although no effect on warfarin (Coumadin®) levels with co-administration of psyllium was reported in one study, administration of these agents should be separated until better research is available.

Due to potential reductions in blood sugar levels caused by psyllium, requirements for insulin or other diabetes drugs in diabetic patients may be reduced. Blood glucose levels should be closely monitored, and dosing adjustments may be necessary.

Other drugs may be affected by psyllium, including anticoagulants, antidepressants, anti-gout agents, anti-inflammatory agents, diuretics, salicylates, tetracyclines, nitrofurantoin, insulin, lithium (Lithobid®, Eskalith®), and digoxin (Lanoxin®). People should speak with their healthcare providers before taking psyllium. Dosing adjustments may be necessary.

Psyllium-containing products may delay gastric emptying time and reduce the absorption of some herbs, supplements, vitamins, or minerals. Absorption of calcium, iron, zinc, and vitamin B12 may also be affected. Other agents should be taken one hour before or a few hours after psyllium to avoid potential interactions.

Psyllium should be used cautiously with other laxatives, such as senna, because effects may be increased.

Psyllium and chitosan together may increase fat excretion in the stool.

Theoretically, psyllium may reduce the absorption of anticoagulant herbs and supplements. However, no effect on warfarin levels by co-administered psyllium was found in one study.

Taking psyllium with herbs and supplements that alter blood sugar may increase the risk of hypoglycemia (lowered blood sugar). People using other herbs or supplements that may alter blood sugar levels, such as bitter melon (Momordica charantia), should be monitored closely by their healthcare provider while using psyllium. Dosing adjustments may be necessary.

Psyllium may interact with herbs and supplements with antidepressant, anti-gout, anti-inflammatory, and diuretic activities.