Don't worry though this isn't one of those illegal medications, it's legal throughout North America. You can tell if a horse is running on lasix by looking for the capital L in the running lines. It's located to the left of the weight carried by the horse in the racing form. If you see an L with a circle around it (some past performances show it as L1) then this means that the horse is first time on the medication.
Lasix is an important factor in handicapping. I always try to re-evaluate a horses performance after a run with lasix. If the horse shows improvement with the medication, then i have to consider new potential. Sometimes you see dramatic improvement with lasix, but most often you see slight improvement.
The racing form will also tell you how a trainer does with first time lasix in his horses. If this percentage is good then it makes another case to watch out for the horse today. Often times a good bet in racing is a horse who improves significantly with lasix. Then takes a class rise in his/her next start. Most people may look at the winning race or improvement as a fluke, but most times their form will hold pretty steady in their next start as well.
My advice is to always re-evaluate carefully a horse after one or 2 races on lasix. If you see no improvement by then, you most likely will not see any. But if you do see improvement then the horse is definitely worth keeping an eye on and might even offer some good value if the conditions suit.
Always remember to look for horse that fits at the level they are racing and try to look for reasons that they might improve today. Lasix is definitely one of those factors that can make a horse improve and often pay you a price at the window. But it is also one of the big x-factors in handicapping, enjoy the challenge. By Kerry Zangara