Blocked bathtub drains are typically caused by a build up, or accumulation, of hair and bathing products. There are several home and commercial remedies to undo or cut through the clogged drain.
A time honored technique is to use a hanger. Straighten it out and put the hook end down the drain and see if you can dig out the blockage that way. Now if the blockage or clog has moved to far down the drain, then this may not work.
Before buying any chemical drain uncloggers consider trying a combination of soda and vinegar. Pour half a cup of each down the drain and let it sit for 10 minutes. Then pour a boiling pot of water down the train and see if this breaks up the clog.
If this is still not effective than there are a number of chemical agents you can purchase that may be powerful enough to unclog the drain.
Some clogs or blockages will be too much for any chemicals to break down. If you’ve reached this point call your licensed plumber and they will snakes and other tools to unblock the drain.