Ferrograd C isn't a good choice of iron supplement. It is a modified release preparation which means that the iron in it is released slowly as it passes through the gut. The problem is that the gut can only absorb iron over a short piece of intestine. So the pill could sail past that bit of the gut and the rest gets "wasted".
The British National Formulary (BNF) has a comment on this problem :
Modified-release preparations of iron are licensed for once-daily dosage, but have no therapeutic advantage and should not be used. These preparations are formulated to release iron gradually; the low incidence of side-effects may reflect the small amounts of iron available for absorption as the iron is carried past the first part of the duodenum into an area of the gut where absorption may be poor.
It is worth reading the whole page and the various sub-sections.
As you can see from that page there are various forms of iron supplement. Iron is poorly tolerated by many people so some experimentation may be required.
I've been taking prescription strength iron supplements for about 18 months now. I absorb iron very badly because of a poorly functioning gut. But for people who absorb it normally it should be possible to fix a deficit within 3 - 6 months.
The ones that I take are :
Ferrous fumarate 210mg, bought in boxes of 84 - this is sufficient for dosing three times per day for 28 days. When I last bought it it cost just over £4 per box, but someone has commented recently that they were charged £5.50.
Prescription strength ferrous fumarate cannot be bought without a prescription from all pharmacists - Boots don't sell it, for example. I buy from Lloyds. Shop around if you have to.
I've also tried ferrous sulphate. I couldn't tolerate that at all. But I have read of some people with the exact opposite experience to me. So, as I said before, you have to experiment.
With each iron pill take 500mg - 1000mg of vitamin C. Iron is constipating, vitamin C may cause diarrhoea. If you get the quantities right you can keep things moving normally. Vitamin C also helps the body to absorb iron. As a bonus it is also good for the adrenal glands.
It is not a good idea to take iron for long periods without regular thorough testing because iron overload is very damaging and poisonous.