Best standard pain killer of cycling

I'll just add my ha'porth here. A proper professional bike fit is essential - and I mean essential - if you're planning to cycle long distances. I now regularly cycle in excess of 100 miles after having one of these and, although I'm pretty knackered, I suffer very little in the way of back pain, etc., despite being well over 6 feet in height.

If your LBS doesn't do this, try a Retul bike fit. I'm afraid it may cost in the region of £150, which I know sounds a lot, but you get all sorts of useful data and measurements that you can transfer to any bike you buy/rent in the future. As an investment in your cycling future, can't be beat.

as per virtually everyone above take your bike to the lbs and get it set up properly. It might cost you the thick end of 100 quid buts its money well worth spent.

No quick fixes. Tinkering is not wise if you get this type of pain or discomfort, as it can suddenly become far far more serious.
I have six ruptured disks in a my spine from poor posture and ignoring signs since I raced as a teenager. It has completely changed my life. A good day is a pain free day.
Get a proper fitting, stop what you're doing if you feel the above and do not medicate to ride, just to get you through until you get help/recover.

But, fear not, a good fit, a SLOW increase in miles and if your body reacts well and some complimentary exercise like swimming or pilates will see you right. You can't just hop on a bike and ride a long way.
A visit to a physio may be a good idea. Don't mess with backs (problems in toes can also be back)!
Best of luck.

+1 Dave

also, masking the pain is bad and it can lead to really bad injuries (like my herniated disc!), try the above advice, and then if thats not working try bike fit.

if you're getting lower back pain it's worth trying moving your saddle slightly forward on the rails, or angling it down at the front just a touch, or lowering it a touch. or a combination of all three. you can also look at raising the bars slightly with a different stem or just rearranging the spacers. also, look for exercises which improve your core flexibility to help you bend from the waist with a straight back.

ibuprofen for me if things start hurting

Pins and needles in your toes might well be caused by incorrectly fitted cleats (I'm assuming you use them) either buy or borrow a decent "guide to cycling" type book which will explain how to correctly fit cleats, or if you have a v. good LBS (local bike shop) they will have a fitting service. Sore small of back may well be caused by bad positioning (bike fit) over reaching/stem too long, again do either of the above for a remedy to that.
Best of luck with your rides in the future.

If you are getting lower back pain and a numb / fizzy foot or toe it would suggest that your bike set up isn't at its optimum. I'd suggest going to your LBS and getting the bike set up properly for height, reach etc but also cleat positions and amount of float.

The best pain killer might be a change of bike-fit, think seatpost height, maybe a different stem, shoe cleat position etc. Ibuprofen is good for inflammation, which is generally the cause of soreness.