Yes, you are correct regarding vitamin C and its possible interactions with some medications.
Although vitamin C is a great vitamin by itself, when it interacts with some medications, it can either increase the medication's effects on the body (i.e. blood pressure - it works WITH blood pressure medication to possibly lower the blood pressure TOO much), and also with anti-histamines (vitamin C also increases the effects of anti-histamines), and also with some tricyclic anti-depressants (wherein it counteracts an anti-depressant's effects, making the medication LESS effective.)
Vitamin C is also known to INCREASE the formation of white blood cells, which as we know may not be helpful in someone with MS where their white blood cells are already too high. It pretty directly interacts with the immune system (to enhance it, not suppress it - suppression of the immune system is the goal of most MS drugs, especially ones like Novantrone), which is probably why a person with certain types or patterns of MS may want to carefully consider or monitor their intake of vitamin C and NOT overdo it. The acidity of Vitamin C may also not be advisable for someone with MS who has bladder problems, as that will exacerbate the condition, not help it. For MSers, there are many other antioxidants that are available that might be better for them to take, if antioxidant properties are what is desired. Keeping the level of vitamin C intake just at the daily recommended dose and not above may be the most desirable.
A quick synopsis of vitamin C:
"Vitamin C has very many functions in the body - some still not completely understood. Below are listed some of the processes in which it is involved:
-Formation of collagen - the body’s intracellular "cement"
-Growth, tissue repair and Wound healing
-Formation of antibodies and stimulation of the white blood cells
-Formation of corticosteroid hormones in the adrenal gland
-Absorption of Iron and its necessary accumulation in the bone marrow, spleen and liver.
-As an antioxidant nutrient, it protects water-soluble substances from oxidation by allowing itself to be oxidised.
-As an anti-histamine, vitamin C reduces the effect of histamine produced by the Immune System. Histamine is responsible for many of the symptoms of allergies such as Hay Fever.
-Carnitine formation in vegetarians, together with lysine.
Vitamin C carries out most of its functions through acting as a powerful antioxidant. This also means that vitamin C is a very effective neutraliser of free radicals - destructive and highly reactive molecules that are thought to be the basis of many serious diseases including cancer and heart disease."
"The vitamin may also interfere with the absorption of tricyclic antidepressants, and it interferes with the results of certain diagnostic blood and urine tests, so you might want to mention your vitamin C intake to your doctor if you take these drugs or are going in for tests."
Of course a slice of lemon in water isn't a big deal at all. It's the mega-doses of vitamin C that need to be carefully considered before taking if you have MS.
Hope this helps.