I know a thing or two about Pharmaceuticals.... I can tell you that
Dulcolax is not known to be safe if taken over long periods of time. There is no data to support it. However it is safe to take occasionally. It works by increasing secretions in the bowel and speeding up peristalsis (ie greases the passage and making things move more quickly)
Sennakot, however is safe to be taken over long periods of time. It is common for elderly patients to take 2 tablets every night for years and years. Senna is just a pergative so it just speeds up the passage of poo
, perfect when you are less mobile as your peristalsis slows too as you age... (the elderly obsession with bowels is, afterall, justified!)
Movicol works using different receptors, is also a purgative, but also adds bulk that remains soft. It's actually very clever! I'm not too sure about long term data.
Lactulose just increases the secretions (greases the way), as it doesn't pass the blood placenta barrier it is safe to take in pregnancy. It is also used in infants and is known to be safe there too.... it is however a sugar laden syrup, which IMO tastes completely foul!
Fibregel is a bulking agent... so it gives you something to get rid of it is by far and away the most natural, gentle method of preventing constipation, but it may take several days before you get a 'result', and is best used as a prophylaxis (preventative) once you have things moving it is advisable to keep taking it... 2-4 times a week is usually sufficient when on a VLCD... remember you're not taking in any where near the volume of food that your body was used to and therefore you cannot expect to 'go' that often. You do have to be able to down the whole glass quickly in one go as the stuff solidifies quite quickly! There is some flavourings in some, the very strict amongst us may say it's not suitable for VLCD.... I personally think it's the lesser of two evils...
Fibre 89 is inulin a natural fibre that is derived from Chicory roots. It's a preventative rather than a cure, so if you have to take a laxative, it's a good idea follow up laxative relief with regular fibre 89 or fibresure to continue to enjoy normal bowel movements!!