they last different amounts of time i have had 5 and each one seems to last that little bit longer. to start with you will be allowed 3-4 within a 12 month period but then it will go to two a year. be mindfull the first one is the worst and does increase your pain as it is tackling all your nerves but it is only for a short period concidering living with the pain on a daily basis. the second you should be pain free for a while and after each injection it will last longer. the procedure is not nice as you will have a local anasthetic so you will be awake throughout, the first few seconds really hurt but then you don't feel the rest of the procedure being done.If your first injection does make the pain worse please continue to injection 2 before making up your mind whether to continue, your specialist should tell you themselves the first one is the worst but then it should start to get better.i really hope i haven't scared you or put you off, i just wish i had some-one to tell me all this at the start and really hope this helps. give it a go.