Pharmaceutical agents called mast cell stabilisers inhibit the release of histamine and therefore its effects. Sodium cromoglycate two per cent is such an agent. It was the first mast cell stabiliser introduced and is the one most used by patients with ocular allergy. This is because it is available as a prescription and pharmacy medication, but is also now widely available from many sources without medical supervision in preserved and single-dose non-preserved forms.
However, it can take several days before its use starts to relieve symptoms, in fact, it is advocated that sodium cromoglycate ideally is used several days before the antigen is encountered. Systemic side-effects are rare but not unknown. Topical side-effects are normally mild and transient. Other mast cell stabilisers are Lodoxamide and Nedocromil.