Can the items in Holland and Barretts aloe vera colon cleanse upset my blood pressure medication.?

If it can interact with your bp medication, it would be because of the liquorice root. Liquorice is a blood thinner. But it really depends on the bio availability of the licorice in the product. Most herbs are devoid of the essential oils that are their "power," or the reason they work in the first place. On the other hand, if it's lost its effectiveness by the way it was processed it's not likely worth taking anyway. I am not saying by this comment that the product is no good. I am unfamiliar with it and therefore can't say one way or another. If you are interested in doing a natural colon cleanse, I'd highly recommend you do as much research on the subject as you can. It's likely that you could find natural means to balance your blood pressure issues instead of medications that can be contraindicated with herbal/natural remedies and then you wouldn't have a problem! :) I can provide you with more information on the subject if you're interested.