Free prescriptions for medical conditions are actually quite limited. On the NHS website it says:
^Medical exemption (MedEx) certificates are issued on application to people who have:
A permanent fistula (for example caecostomy, colostomy, laryngostomy or ileostomy) requiring an appliance or continuous surgical dressing.
A form of hypoadrenalism (for example Addison's disease) for which specific substitution therapy is needed.
Diabetes insipidus or other forms of hypopituitarism.
Diabetes mellitus, except where treatment is by diet alone.
Hypoparathyroidism.
Myasthenia gravis.
Myxoedema (hypothyroidism requiring thyroid hormone replacement).
Epilepsy requiring continuous anticonvulsive therapy.
Continuing physical disability which means the person can't go out without the help of another person. Temporary disabilities do not count even if they last for several months.
You are also issued with a MedEx if you are undergoing treatment for cancer. This includes treatment for the effects of cancer or for the effects of cancer treatments.^
I had asthma when I was younger. Grew out of in my early 20's. While the prescription charge is £7.20 a standard ventolin inhaler contained 200 doses the last time I had one so it lasts a fair bit.