Welcome to Healing Well, abseeley! I'm sorry that you have been ill for so long. I was almost relieved when they finally came up with a name for my long term gut problems. Then I got anxious. What a rollercoaster of emotions....
Mezavant is a brand name of a medication used here in the US called Lialda. This medication is a long-lasting Mesalazine (5-aminosalicyd acid or 5-ASA). Mesalazine is a very common medication that people with CD and UC often take. Shorter acting mesalazine products are called Pentasa and Asacol.
In everything I have read, drowsiness is not a side effect of these meds. BUT people with sensitivity to aspirin could have some serious reactions to these meds. Please review the side effects list at the following site. If you have any that fall under the stop taking immediately section, do that and consult your doctor now. Mezavant Drug Fact Sheet
Moderator Crohn's Disease Forum
CD, Ankylosing Spondylitis, lupus, small fiber peripheral neuropathy, avascular necrosis, peripheral artery disease, degenerative disc disease, and a host of other medical problems.